Design and Construction of a Commercial Aftermarket Automotive Head-Up Display

by Donn Eric Pasiliao

A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Mechanical and Industrial Engineering University of Toronto

c Copyright by Donn Eric Pasiliao 2014 Design and Construction of a Commercial Aftermarket Automotive Head-Up Display

Donn Eric Pasiliao Master of Applied Science Mechanical and Industrial Engineering University of Toronto 2014

Abstract The contents of this report provides a comprehensive look at the details involved in the design and development of an automotive head-up display (HUD). By examining the product’s complete assembly, including its optics, mechanical assembly, and embedded system, a portable aftermarket automotive HUD was successfully constructed. The resulting product addresses issues and criticisms present in commercially available HUDs, such as display clutter, placement, price, and versatility, giving it a strong competitive advantage within its target market. A brief overview on some performance improvements is also included, followed by recommendations for future actions to advance the developed product closer to commercialization.

ii Acknowledgments

I would like to thank my supervisor, Professor Ridha Ben Mrad, for providing me with a perfect balance of direction and creative freedom during my M.A.Sc. program. Throughout the course of this project, his guidance allowed me to consistently maintain a strong sense of enthusiasm for the project, even under seemingly insurmountable challenges. Also, I would like to thank the MIE Machine Shop staff (Ryan Mendell, Fred Gebeshuber, Jeff Sansome, Terry Zak, and Keith Hockley) for teaching me practical machining techniques and practices. If it weren’t for their patience during fabrication, the mechanical assembly would not have the precision necessary for the product’s optics. Furthermore, I would like to thank my colleagues at the Mechatronics and Microsystems Design Laboratory (MMDL): Alaeddin Bani Milhim, Steffen Blume, Faez Ba Tis, Ali Madani, Vainatey Kulkarni, and Khalil Zahar. Their lively discussions, technical support, and consistent words of encouragement has been invaluable in creating an exciting and creative work atmosphere during the course of my M.A.Sc. program. Lastly, I would like to extend my deepest gratitude to my family for their continuing support through life’s many challenges, academic or otherwise.

iii Contents

1 Introduction ...... 1 1.1 Motivation ...... 1 1.2 Competitive Analysis ...... 3 1.2.1 Google Glass ...... 3 1.2.2 Garmin HUD ...... 7 1.2.3 Design Criteria ...... 10 1.3 Thesis Outline ...... 11 2 Design and Fabrication ...... 12 2.1 Micromirror ...... 14 2.2 Optics ...... 14 2.2.1 Projection Film ...... 15 2.2.2 Laser ...... 15 2.2.3 Magnifying Lenses ...... 20 2.3 Mechanical ...... 22 2.3.1 Materials ...... 22 2.3.2 First Optical Fixture Design ...... 23 2.3.3 Final Optical Fixture Design ...... 27 2.3.4 Complete Assembly ...... 30 2.4 Electronics ...... 31 2.4.1 Power Management ...... 32 2.4.2 Microcontroller ...... 35 2.4.3 Digital to Analog Converter ...... 42 2.4.4 Laser Modulation and Driver ...... 47

iv Contents v

2.4.5 High Voltage Amplifier ...... 48 2.4.6 Wireless Communication ...... 51 2.5 Software and Microcontroller Firmware ...... 53 2.5.1 The Look-Up Table ...... 53 2.5.2 Microcontroller Firmware ...... 55 3 Display Performance ...... 59 3.1 Controls ...... 59 3.2 Versatility ...... 60 3.3 Final Product ...... 62 3.3.1 Directions ...... 63 3.3.2 Notifications ...... 64 4 Conclusion and Recommendations ...... 66 4.1 Recommendations ...... 67 Appendices ...... 74 A Optics ...... 75 A.1 Zemax Model 1 ...... 75 A.2 Zemax Model 2 ...... 76 A.3 Zemax Model 3 ...... 77 A.4 Zemax Model 4 ...... 78 A.5 Zemax Model 5 ...... 79 B Mechanical Drawings and Assembly ...... 80 B.1 Optical Test Fixture ...... 80 B.2 Final Product Parts and Assembly ...... 92 C Electronics ...... 100 C.1 Power Management Circuit ...... 100 C.2 Microcontroller and Peripherals ...... 102 C.3 High Voltage Amplifier ...... 105 C.4 Digital to Analog Converter Selection Chart ...... 107 D Software ...... 108 List of Figures

1.1 Google Glass ...... 4 1.2 Google Glass Display ...... 5 1.3 Space Glass Display ...... 7 1.4 Garmin HUD ...... 8 1.5 Garmin HUD VFD ...... 9

2.1 Micromirror Design ...... 12 2.2 Actuated Micromirror ...... 13 2.3 Micromirror Rotation ...... 13 2.4 Light Spill Around Micromirror...... 16 2.5 Exclamation Mark Projected Without Additional Optics ...... 17 2.6 Optical Assembly With an Added Pinhole Aperture...... 18 2.7 Optical Assembly With the Bi-convex Lens ...... 19 2.8 Exclamation Mark Projected With Pinhole Aperture ...... 20 2.9 Final Optical Assembly ...... 21 2.10 Effect of an Additional Magnification Lens to Scanning Angle ...... 22 2.11 Complete Assembly of the First Optical Fixture Developed ...... 23 2.12 Initial Design of XY Stage ...... 24 2.13 Exploded View of XY stage ...... 24 2.14 Linear Stage Mechanism of the Micromirror Stage ...... 25 2.15 Adjustable Lens Fixture ...... 26 2.16 Laser Barrel ...... 27 2.17 Final Optical Fixture Design ...... 28

vi List of Figures vii

2.18 Linear XY Stage ...... 29 2.19 Laser Barrel Assembly ...... 30 2.20 Final Product ...... 31 2.21 Power Management Schematic ...... 32 2.22 Microcontroller Schematic ...... 36 2.23 Individual SS Pin SPI Configuration ...... 38 2.24 Daisy Chain SPI Configuration ...... 38 2.25 Continuous (left) vs. Non-Continuous Vector (right) ...... 42 2.26 DAC Schematic ...... 43 2.27 Voltage Output Verification ...... 45 2.28 AD5684 Configuration ...... 47 2.29 AD5684 Input Shift Register Contents ...... 48 2.30 Load Switch Circuit for Laser Modulation ...... 49 2.31 High Voltage Amplifier Circuit ...... 50 2.32 RN42 Bluetooth Schematic using a UART interface ...... 51 2.33 Smartphone Bluetooth SPP Software with the Output Image ...... 53 2.34 Microcontroller Firmware Code ...... 55 2.35 SPI Function ...... 57 2.36 AD5684 Command Bits and Addressing Mode ...... 57

3.1 Vector Trace Path for Two-Digit Numerical Display ...... 61 3.2 Resulting Display of the Vector Trace Path for Two-Digit Numerical Display 61 3.3 Physical Prototype ...... 62 3.4 Final HUD Screen ...... 63 3.5 Left Arrow ...... 63 3.6 Right Arrow ...... 64 3.7 Danger ...... 64 3.8 Exclamation Mark ...... 65 3.9 Mail ...... 65

C.1 Power Management Bill of Materials (BOM) ...... 100 List of Figures viii

C.2 Power Management Schematic ...... 101 C.3 Microcontroller BOM 1 ...... 102 C.4 Microcontroller BOM 2 ...... 103 C.5 Microcontroller Schematic ...... 104 C.6 High Voltage Amplifier BOM ...... 105 C.7 High Voltage Amplifier Schematic ...... 106 C.8 DAC Selection Chart ...... 107

D.1 Programming Code 1 ...... 108 D.2 Programming Code 2 ...... 109 D.3 Programming Code 3 ...... 110 D.4 Programming Code 4 ...... 111 D.5 Programming Code 5 ...... 112 D.6 Programming Code 6 ...... 112 Chapter 1

Introduction

Head-up displays (HUD) are increasingly becoming a norm in the automotive sector. Once limited only to the world of aviation, HUD technology is beginning to extend its grasp into the consumer automotive market due to its numerous safety benefits and rapidly declining cost. Currently, the automotive sector is the second largest revenue generator in the HUD market in the United States, and this is only expected to grow within the next five years as implementation begins to extend beyond luxury vehicles and into the low- and medium-end automotive segment [1]. The purpose of this chapter is to provide an overview of the motivation behind incorpor- ating HUDs into automobiles, the state of the HUD technological landscape, and a brief outline detailing the report’s structure.

1.1 Motivation

In a general sense, a HUD is a device that projects information, such as vehicle data or navigation instructions, onto a transparent screen. It is a technology that was initially introduced by the aviation industry to reduce the visual scanning required between two separate displays, the instrument panel (head down display (HDD)) and the windscreen. By superimposing graphics typically found on HDDs onto the windshield, pilots are now able to maintain visual contact with the far domain while also receiving important flight data [2]. Throughout its increasingly widespread use across aviation, several studies have docu-

1 1.1. Motivation 2

mented the benefits of implementing HUDs into the cockpit. In [3], May et al. outlined the four main advantages that motivate the application of HUDs in modern aircrafts:

1. Reduce the time spent looking away from the forward field view

2. Reduce the need to refocus the pilot’s eyes, which occurs in the transition between the control panel and the far domain

3. Provide spatial feedback of objects in the far domain through conformal symbology

4. Display more accurate and representative symbols than traditional dials and gauges.

These advantages resulted in an increase in aviation safety, which became the primary motivation to introduce the HUDs into automobiles. The first automotive HUD was first introduced by General Motors in their 1988 Oldsmobile Cutlass Supreme Indianapolis 500 Pace Car Parade Convertibles [4]. Due to the cost and physical size of the HUD, however, its design was not considered to be a success [5]. Despite this, it nevertheless pioneered the technology which, since then, has seen a much greater mainstream adoption, although still limited, by the automotive and consumer electronics (section 1.2). This led to several studies that examined the effects of translating industries the technology from the world of air-travel to the hands of everyday consumers. In [6], Liu et al. compared the effects of using head-up vs. head-down displays on a commercial vehicle driver’s driving performance. In the study, each of the twelve participants were asked to complete four tasks: speed detection/maintenance, navigation, emergency reaction, and commercial goods delivery1. On this basis, the study showed that the imple- mentation of a HUD in a commercial vehicle provides a significant improvement in a driver’s response time to a sudden event and in maintaining a consistent speed while driving. Similar studies under different environments have been done, and the results of each have largely supported this claim [7–9], thus validating the improved safety benefits that a HUD offers over a traditional HDD console in a consumer automotive application. In spite of these benefits, the adoption of automotive HUDs still remains fairly limited. As of 2010, only 1 percent of new vehicles offer a HUD as a standard in their base models.

1For commercial goods delivery, information pertinent to the delivery, such as receipt number and package information, were displayed [6]. 1.2. Competitive Analysis 3

Although this is expected to grow ninefold by 2020 [5], a large majority of the cars produced today will endure without HUDs for the remainder of each of their life cycles. Therefore, the focus of this project was to develop a product that will provide consumers with a portable aftermarket HUD that matches or improves on the display quality of the current state of commercially available HUDs, affording the average consumer with the same safety benefits offered by the current line of luxury automobiles.

1.2 Competitive Analysis

Prior to designing the HUD, a brief assessment of the current technological landscape was completed to provide the product development process with a reference, or benchmark, to improve upon. This assisted in informing the design criteria and objectives by which the final product was based on. By performing this comprehensive analysis, the HUD was designed to be a technologically and economically competitive tool in improving automobile safety for its target market. To maximize the final product’s competitive advantage, this analysis was not strictly limited to other aftermarket automobile HUDs. Some of the products that were examined fall within a more broad spectrum of HUDs, including wearable devices such as Google Glass and Space Glass. The competitive analysis then concludes with a summary of one of the first commercially available aftermarket HUDs, the Garmin HUD.

1.2.1 Google Glass

One of the products that was examined for its capability as a HUD was Google Glass. Google Glass is a wearable HUD that comes in a form similar to a pair of eyeglasses (figure 1.1). It is designed to be an unobtrusive display that is able to project information from a wireless device onto a semi-transparent screen [10]. Although Google Glass is marketed as a general consumer electronics product, it offers similar benefits as an automotive HUD and is functionally capable of operating in the same manner. Therefore, it was selected to be included in this study. In principle, Google Glass operates much like a typical projection module where an image 1.2. Competitive Analysis 4

Figure 1.1 Google Glass [11] 1.2. Competitive Analysis 5 from a light source is displayed on a reflective or diffusive surface. What distinguishes Google Glass, however, is that this assembly of the projector and screen has been miniaturized to fit the portable form factor of a head-mounted device. Using a mini-projector encased within the HUD’s plastic band, an image received wirelessly from an external device is projected onto a semi-transparent film embedded inside a small prism (figure 1.1). This carefully angled prism then redirects the light into the user’s pupil in order to focus the image onto the fovea region of his/her retina. This results in a display that simultaneously includes the user’s surroundings and a well-focused digital image [11], as shown in figure 1.2.

Figure 1.2 Google Glass Display [10]

Preceding its launch, Google Glass garnered a lot of publicity and attention for its potential as a HUD [12–14]. However, since its release in 2012, it has been met with some criticism due to its drawbacks, particularly with regards to its screen placement [15] and functionality [16]. One cause for concern that has been raised for Google Glass has been the unaccommod- ating placement of its display. Initial firsthand reports from the product’s early adopters have consistently reported experiencing discomfort after short-term and long-term use of the product [17–19]. According to Dr. Eli Peli, the optomoterist Google consulted for the project, this pain is attributed to the eye movement required to view the display on 1.2. Competitive Analysis 6 the top-right corner of the user’s field of view; if users are not acclimated to looking in a particular direction, the muscles around the eye would need time to adjust accordingly, causing discomfort as it adapts to a new routine [17]. Thus, if a user’s daily activities do not require him/her to focus his/her eyes on the top right corner of their view, headaches from constant use of Google Glass will consequently follow. For the application of an automotive HUD, studies and surveys have been done regarding the optimal placement of the HUD’s display [20–22]. Specifically, in [21], Yoo et al. found that, of its 40 participants, 57% of them generally preferred the HUD image to be projected below their line of sight, with a slight bias to the left or right of centre. This showed consistency with the results found in [22] where its 24 subjects identified the corner locations to be the worst placement for a HUD, further contradicting Google’s design decision on Glass’ display location. Another drawback that Google Glass has been criticized for is that it provides the user with access to too many display features. Aside from navigation, Google Glass also allows users discreet access to notifications from a smartphone and video content. This has caused traffic enforcement groups to raise concerns on whether drivers are solely using the wearable device for navigation and vehicle information while driving [23]. Because of this, it has developed some controversy around its use as a HUD tool for automobiles, with some traffic regulations beginning to restrict the use of Google Glass behind the wheel of a car [24]. In [25], a review was done on the effects of visual clutter in aviation HUDs on pilot performance. Due to the increasing complexity of modern cockpits, the large amount of information pilots have to constantly interact with, simultaneous to the already demanding task of flying, had to be reduced to minimize the visual workload of the pilot. This meant eliminating irrelevant information that are not related to the primary task at hand. In the case of Google Glass, its display should only contain the most fundamental information needed to assist the driver in navigation or in operating his/her vehicle in order to function as a safe automobile HUD. Hence, for the design of the HUD discussed herein, some consideration was placed on the type of information displayed on the driver’s windscreen. Since Google Glass’ announcement, other wearable HUDs that work under the same principle have been developed. Space Glass, for example, is a product that is expected 1.2. Competitive Analysis 7 to be a strong contender against Google Glass once both are released. It is a wearable device that, rather than using a small window for its display, uses a transparent screen that encapsulates a majority of the user’s field of view to present a stereoscopic display of images from an external device [26]. Although the size of its display may address the issue of screen placement the Google Glass suffers, it introduces a more severe potential for display clutter due to the product’s wide array of applications and the real estate the display occupies in the user’s field of view [27]. Therefore, qualifying the Space Glass to be an automotive HUD may lead to a similar level of scrutiny that Google Glass is experiencing for its ability to meet proper safety standards and regulations. A sample of the concept, and what can be displayed using Space Glass, has been included in figure 1.3.

Figure 1.3 Space Glass Display [28]

1.2.2 Garmin HUD

Another class of products that were examined prior to the development of the HUD were other aftermarket automobile HUDs. One of which is the Garmin HUD, an aftermarket automotive HUD that connects to a smartphone via Bluetooth to project vehicle information on a transparent film on the car’s windshield (figure 1.4). This product was released in 2013 and still remains, as of the date of this report, the only widely available aftermarket HUD in the market. 1.2. Competitive Analysis 8

Figure 1.4 Garmin HUD [29]

As an automotive HUD, the design of the Garmin HUD has been streamlined to address some of the issues present in head-mounted displays like Google Glass and Space Glass: its placement on the dashboard allows it to be situated at the bottom of the user’s line of sight, and its limited capability ensures that it can only be used to display pertinent information to the driver. However, despite these advantages, the Garmin HUD still garnered some criticisms, particularly with its price and severely limiting display format. One critique the Garmin HUD has received from multiple outlets, including users and journalists [30–32], has been for its relatively high price tag. Currently, it has a manufacturer’s suggested retail price (MSRP) of $149.99 USD [29], which also requires Garmin’s proprietary GPS smartphone software, Garmin StreetPilot or NAVIGON, for an additional $39.95 to $86.872 [33]. Since the product relies heavily on a smartphone to process GPS data and generate navigation information, most of its early adopters have commented on the price as being too expensive for what they consider to be merely an accessory [32]. This is then further supplemented by considering that fully capable GPS devices are available for as low as $100 [34]. Furthermore, in [35], Guo et al. conducted a survey that consisted of 539 individuals in China where it showed that there still remains a fairly large contingent of drivers who are not familiar with the existence of HUDs in automobiles; of its subjects, 63.08% admitted to being unaware of HUD systems. This combination of a lack of awareness

2The price of the software varies depending on which country the software will be used in. 1.2. Competitive Analysis 9 and an expensive barrier to entry has caused the adoption rate for aftermarket HUDs to remain low. Therefore, in order for an aftermarket HUD to effectively compete and to improve its adoption rate, the total cost to produce and manufacture the HUD should be minimized. Another drawback critics have mentioned regarding the Garmin HUD has been its highly restrictive display [36]. The Garmin HUD uses a bright vacuum flourescent display (VFD) that contains a fixed array of numbers and arrows, as shown in figure 1.5. This means that the arrangement of the information or the design of the navigation tools are dictated by the product, with no room for the user to customize it to his/her preferred settings or aesthetic. For example, although it is able to display navigation instructions for the next junction, some users have criticized it for failing to provide information for the ones after [37]. With the Garmin HUD’s fixed system embedded in its hardware, any update that could potentially allow this feature would require a complete redesign of the system instead of a simple software update. This, in effect, could shorten the product’s life cycle by eliminating its chance to accommodate for changing market demands and user feedback [38]. Hence, in designing the HUD, criteria was established to strike a balance between allowing the product with enough versatility without generating unnecessary display clutter.

Figure 1.5 Garmin HUD VFD [36] 1.2. Competitive Analysis 10

1.2.3 Design Criteria

Using the information gathered on commercially available HUDs, a design criterion was established. Apart from being able to perform fundamental functions associated with HUDs, such as displaying an image on a transparent surface and wireless communication, the following were also considered:

HUD Placement. The HUD should be able to display information at a secure and comfortable location for the user by allowing it to be situated below his/her line of sight.

Price. Each component that is included in the product assembly must be consciously selected such that each peripheral is economical without compromising on technological capability.

Versatility. The display should allow for reconfiguration, either through the system’s embedded firmware or through an external software update. Furthermore, a secondary objective of minimizing the size of the final prototype for portability was accounted for. In order to achieve this, a preliminary decision was made to structure the device such that it projects a real, rather than a virtual, image. Although most HUDs in automotive and aviation project a virtual image to create optical distance, they also require a significant amount of volume to accomodate for the collimating optics needed to mimic distance [39]. Furthermore, [5] presents an argument that illustrates how projected HUDs show a stronger potential for innovation due to its generally wider field of view, opening up such possibilities as augmented reality through accurate conformal mapping [40]. Therefore, since the scope of this project is to create a consumer aftermarket HUD, the design parameter to make the final product bright and compact took precedence over projecting a virtual image with an optical distance. 1.3. Thesis Outline 11

1.3 Thesis Outline

The structure of this report has been arranged to provide the reader with a detailed view of the product development process involved in the design and development of the automotive HUD. The goal of this report is to relay enough information on the components included in the scope of this project such that the next design iteration is informed with the current generation’s strengths and drawbacks. Each of these components are explored comprehensively in the subsequent chapter, Chapter 2. This is then immediately followed by a brief overview of the performance improvements done on the product’s prototype, Chapter 3. Finally, it concludes with an assessment of how the final product meets the initial criteria described in section 1.2.3 and a set of recommendations for future improvements, Chapter 4. Chapter 2

Design and Fabrication

The final design of the automotive HUD involves the assembly and integration of several optical, mechanical, electronic, and software components. The operating principle of the projection module begins by emitting and modulating a monochromatic laser towards a micromirror placed on a 70◦ angle against the laser’s axis. The reflective micromirror is then rotated at high speeds to redirect the light to a screen, resulting in the projection of vector-traced images with frame rates greater than 24 frames per second. The micromirror, driven by four repulsive-force electrostatic actuators (figure 2.1), is controlled by subjecting each of them, initially, with 200V to substantially lift the micromirror from the substrate (figure 2.2). From there, the voltages applied on each of the actuators are varied between 0V and 200V to rotate the micromirror as needed (figure 2.3) [41].

Figure 2.1 Micromirror Design [41]

12 13

Figure 2.2 Actuated Micromirror [42]

Figure 2.3 Micromirror Rotation [41] 2.1. Micromirror 14

This chapter outlines the component selection, fabrication, and assembly procedures involved in constructing the final product. It includes a summary of the micromirror design that was used, steps taken in shaping the complete optical assembly, fabrication techniques in constructing its mechanical components, a full electrical schematic of the embedded system, and an overview of the logic behind the product’s firmware.

2.1 Micromirror

The micromirror used in the design, figure 2.1, is based on a patented translating and rotating micro-mechanism designed by Prof. Siyuan He and Prof. Ridha Ben Mrad [43]. It is composed of a 1.0mm reflective mirror plate that is actuated using repulsive electrostatic forces applied to four separate repulsive-force actuators (figure 2.1). By applying voltages between 0V and 200V to each of the fixed fingers, the mirror can be translated (figure 2.2)or rotated with a maximum scanning angle of ±2.5◦ at high speeds and an accuracy presented in [41]. These features permitted the use of this micromirror design for vector display applications, as was validated by [41]. Also, this micromirror was developed around the PolyMUMPs fabrication method, a four-layer foundry surface micromachining process capable of volume production [44]. Since the actuator only requires two polysilicon layers, only Poly0 and Poly1 are required, leaving the Poly2 and the metal layers out of the overall process [41]. For the purpose of ease of manual assembly, the micromirrors used were packaged in a standard 44 CQFP chip. However, if further miniaturization is required, other custom packaging techniques may be used [45].

2.2 Optics

In order to display a bright and high-contrast image, an emphasis was placed on selecting the appropriate readily-available optical components. This includes a proper transparent projection film, laser module, and lenses for laser focusing and image magnification. The complete optical design was then validated using custom-fabricated fixtures. 2.2. Optics 15

2.2.1 Projection Film

The transparent projection film used is a product manufactured by Sun Innovations called an Emissive Projection Film. It is a film capable of displaying monochromatic, dual color, and full RGB images on a clear surface (> 90 % transparency [46]) with minimal optical haze (< 2% [46]) using a projector capable of transmitting a range of semi-discrete violet-blue wavelengths centered around 375nm, 405nm, and 450nm [47]. Since ultraviolet light has a shorter wavelength and higher energy than visible light, the particles in the flourescent material down-converts the ultraviolet light’s energy into visible light, thus only emitting visible light in regions that have been excited by electromagnetic radiation. This ensures that the rest of the film remains transparent and haze-free [48]. In order to display various colours, different light emitting particles are introduced into the film material. For example, Europium is included to display red, Terbium for green, and Cerium (and/or Thulium) for blue. Each of these additives then allow a range of wavelengths centered around each colour to be emitted, with the corresponding level of each dictated by the transmitted wavelength’s deviation from the center wavelength. This allows the film to emit the full visible spectrum by appropriately selecting the wavelength and intensity of the transmitted light [48]. For the purpose of this project, a laser diode centered around a 405nm wavelength was used to transmit, or excite, the particles within the Emissive Projection Film.

2.2.2 Laser

Ideally, based on the projector’s principle of operation, all of the light emitted from the laser will be redirected by the micromirror. In this way, the laser’s optical power can be fully exploited to display a bright, high-contrast image on the projection screen. However, lasers with a precise diameter, especially a diameter less than the 1mm diameter of the micromirror, introduce a significant addition to the product’s total cost. Therefore, an optical lens configuration to adjust for this was developed. 2.2. Optics 16

Previous Design

In the previous iteration of the HUD design, a well-collimated 532nm laser was used as the light source for the projector [41]. It had an operating voltage and current of 3.3VDC and 1.2A, respectively, which produced a 1.0mm collimated green circular beam with a 1mrad divergence [49]. However, since the micromirror plate already has a 1.0mm diameter, placing it on a 70◦ angle against the laser’s axis reduced its reflective area to much less than the laser’s beam diameter. This caused some of the light to spill outside of the micromirror, effectively reflecting, not only the light coming from the micromirror, but also the light that spilled onto the surrounding actuators. This effect is shown in figure 2.4, where the laser has been broken up into five beams to represent its boundaries. From this figure, due to the size of the collimated laser, only three of the five beams are reflected by the micromirror; the two beams that fall outside of the micromirror become incident to its micro-mechanism, resulting in the unwanted reflection of the micromirror’s periphery appearing on the windshield. This results in a vector-traced image that is surrounded by the image generated by the reflection of the mirror’s micro-mechanism or its periphery, as shown in figure 2.5.

Figure 2.4 Light Spill Around Micromirror.

Initially, this problem was addressed in [41] by introducing a 900µm pinhole to act as an aperture for the laser. This, in effect, limited the laser beam diameter incident to the 2.2. Optics 17

Figure 2.5 Exclamation Mark Projected Without Additional Optics micromirror module to 900µm by masking the excess light using the pinhole such that the light transmitted by the projector is only coming from the micromirror plate; light spilling outside of the micromirror is eliminated (figure 2.6). Despite successfully removing the unwanted reflection on the display, this solution also introduces a number of inefficiencies and drawbacks. The added pinhole reduces the laser power output by 10%, since much of the light diffuses on the aperture. Also, by adding another component along the laser’s optical path, the product’s optical assembly is further complicated due to the tight tolerances required to maintain an accurate alignment necessary between the laser, the pinhole, and the micromirror. Furthermore, in order to minimize light divergence past the pinhole, the tolerance required to ensure beam divergence is less than 1mrad add significant cost to the laser module; for example, the laser used in the previous design costs $985 from World Star Tech [49]. Therefore, in order to advance the HUD closer to commercialization, a redesign was done to address these issues.

Redesign

The proposed alternative is to use a more cost-effective laser module that minimizes overall loss in optical power, while also simplifying the product’s optical assembly. The approach to this redesign was twofold: improve the optical power efficiency first before addressing the issues regarding assembly and cost simultaneously. To increase the optical power efficiency, a bi-convex lens was used in place of the pinhole aperture. In the simulation model shown in figure 2.7, a bi-convex lens with a 200mm 2.2. Optics 18

Figure 2.6 Optical Assembly With an Added Pinhole Aperture. effective focal length (EFL)1 from Edmund Optics (part #48-263) was placed ahead of the collimated laser used in [41]. This, in effect, focused the laser to reduce its beam diameter to an appropriate size (< 1mm) before it hit the micromirror. The micromirror was then put in an area where the laser beam diameter has been significantly reduced to < 1mm. In this case, the micromirror was positioned 450mm in front of the focusing lens where the beam diameter has been reduced to approximately 0.5mm. This ensured that no light spilled around the periphery of the micromirror plate, thus eliminating the unwanted projection of its mechanism (figure 2.7). This model was verified using the fixture detailed in section 2.3.2, which successfully resulted in a bright vector-traced image that did not contain any of micromirror’s surrounding mechanism or the outline of its periphery (figure 2.8). To address the issue of cost, a significantly less expensive laser module with less collimation was examined. In the HUD prototype, a laser module from Laserlands that comes in a variety of wavelengths, including 405nm and 450nm, was used. The module assembly comes complete with an assembly of components to power the laser diode, which include its basic driver circuit, the laser diode, and a focusing lens that can be adjusted using a

1A long focal length was selected to accommodate for the geometric limitations of the optical table. 2.2. Optics 19

Figure 2.7 Optical Assembly With the Bi-convex Lens2 screw mechanism. Due to this laser’s relatively low level of collimation, it is substantially less expensive than the previous model; this particular 405nm laser module costs $13.50 [50], while the highly collimated laser costs $985. Also, this lack of collimation was used to the HUD design’s advantage. Instead of parallel rays, the light coming from the module actually has a fairly significant convergence because of its focusing lens. This eliminated the need for the external bi-convex lens, further reducing the cost of the optical assembly. Moreover, since the focusing lens is attached using a screw mechanism, alignment was considerably improved over the pinhole or the bi-convex lens assembly design. In the previous laser assemblies, the pinhole and focusing lens did not have a direct physical link to the laser diode, which could result to misalignment due to external forces and vibration. By using a screw mechanism to adjust the focusing lens, alignment between the laser source and lens is better maintained during product assembly and operation because of its more rigid connection. 2.2. Optics 20

Figure 2.8 Exclamation Mark Projected With Pinhole Aperture

2.2.3 Magnifying Lenses

In order to produce a visibly large image on the windshield, a bi-concave lens was used as a magnification lens in the HUD’s optical assembly. This lens worked to effectively amplify the scanning angle of the micromirror’s two axes as it traces the vector image on the display. To achieve the largest amplification possible, the selection criterion for this lens was based on a bi-concave lens with the shortest available focal length. In this case, lens #47914 from Edmund Optics was used, which has a −6.00mm EFL and an aperture of 6.00mm [51]. In the HUD’s final design, the magnifying lens was situated by finding the focal point of the focusing lens using trial and error. This resulted in magnifying the micromirror’s scanning angles from ±2.5◦ to approximately ±12◦ – an angular magnification of 4.9 – in both rotation axes (figure 2.9). Also, to maximize the amount of optical power that transmits through the lens, some consideration was placed on the anti-reflection coating used for the magnification lens. For this particular HUD design, since the lasers used will be in the violet/blue region (405nm and 450nm), a lens coating that minimizes reflection of these wavelengths was selected, namely the VIS 0◦ coating from Edmund Optics. Unlike other coatings, the VIS 0◦ coating reflects less than 1% of incident light from wavelengths in the visible spectrum (405nm to 675nm) [52]. This maximizes the optical power that is transmitted through the lens, resulting in a bright, high-contrast image on the windshield. Although further angle magnification can be achieved using an additional bi-concave lens 2.2. Optics 21

Figure 2.9 Final Optical Assembly

(figure 2.10), the power loss after the second lens, from experimentation, was too significant and the projected image on the screen was not bright enough to be considered visible. This may be due to the combination of the lens material and anti-reflective coating used on the readily-available lenses from lens retailers [53]. Therefore, if a higher angular magnification is required, the anti-reflection coating and lens material would have to be optimized according to the specific laser wavelengths used in the projector. After assessing the drawbacks of the optical assembly of a previous projector design, a revised lens configuration was developed. This resulted in a significant improvement in the HUD’s optical performance and efficiency, and its economic value. For a detailed view of the optical configuration for each of the Zemax models, please refer to Appendix A. 2.3. Mechanical 22

Figure 2.10 Effect of an Additional Magnification Lens to Scanning Angle

2.3 Mechanical

Since the assembly of all the components was custom to this design, much of the mechanical parts used had to be manually fabricated using tools available in a machine shop. For the HUD prototype, these components were machined using a manual mill and lathe. This introduced design constraints specific to the limitations and capabilities that such tools allow for. This section of the report will detail the various considerations that were accounted for in the design of the product’s mechanical assembly, including materials selection, geometrical compromises, and human interface design decisions.

2.3.1 Materials

The material that was used to fabricate the mechanical components of the device was Delrin. Known for its good dimensional stability and excellent machinability, Delrin offers the versatility and low density often associated with plastics while also exhibiting metal-like mechanical properties on strength and stiffness [54]. Also, due to its increasingly widespread use in a variety of industries, and despite its excellent mechanical properties [55], Delrin remains a financially competitive material, even among some of its plastic counterparts [56]. 2.3. Mechanical 23

Therefore, Delrin was selected to be suitable material for most of the parts used in the HUD’s mechanical assembly. During fabrication, these properties exhibited well on a manual mill and lathe; the material was able to undergo the high pressure and temperature conditions of each tool without experiencing considerable melting or warping. This allowed for the ease of production of small components, while also allowing for dimensional accuracy.

2.3.2 First Optical Fixture Design

To verify the concept of replacing the pinhole with a bi-convex lens, and to experimentally determine the practical distance required between each optical component, a simple but versatile optical fixture was developed and constructed (figure 2.11). This optical fixture was designed to overcome the geometric limitations of the optical table during optics verification; using this fixture, both the magnifying and focusing lenses were finely adjusted within a few millimeters away from the micromirror module, an affordance which was not possible with the optical table. This section details the different components and subassemblies included in this fixture, which permitted the precise level of lens adjustment required.

Figure 2.11 Complete Assembly of the First Optical Fixture Developed 2.3. Mechanical 24

Linear XY Stage

So as to adjust for any misalignment during the wire-bonding and packaging of the micromir- ror, a small linear XY stage was developed (figure 2.12). The complete labeled assembly of the apparatus is included in figure 2.13.

Figure 2.12 Initial Design of XY Stage

Figure 2.13 Exploded View of XY stage

To finely position the micromirror for optical alignment, a linear stage mechanism with a 0.5mm thread size was implemented on the XY stage. In reference to figure 2.14, the stage 2.3. Mechanical 25 would translate in the positive direction of one axis if the corresponding screw is turned clockwise, negative if the screw is turned counter-clockwise. This is made possible by an assembly composed of a slotted platform (Platform 1), an angle block (Platform 2), two carriages, two roller bearings, two M3 x 16mm screws, and two springs (figure 2.13). Per axis, the head of an M3 x 16mm screw is fixed on to a roller bearing using a nut, which was press-fitted against a carriage that was attached to a platform (Platform 1) using horizontal or vertical slots. This assembly effectively constrains the screw axially, while also allowing it with enough freedom to rotate and move along a path perpendicular to each screw’s assigned axis. In order to translate the screw’s rotation into linear motion for the stage, the threaded end of the screw was coupled with corresponding M3 holes embedded on the sides of the stage. This assembly was applied to both the x and y axes, permitting for small and precise linear adjustments of the micromirror to improve optical alignment. Furthermore, to achieve the required 20◦ angle of the micromirror, and to fasten the carriages, the assembly was then mounted on a 20◦ angle block (Platform 2).

Figure 2.14 Linear Stage Mechanism of the Micromirror Stage 2.3. Mechanical 26

Figure 2.15 Adjustable Lens Fixture

Lens Housing and Adjustment

For accurate adjustments of both the magnifying and focusing lenses, each lens was assembled into a linear adjusting mechanism (figure 2.15). Each lens was press fitted into a threaded lens carriage, which allowed for its linear adjustment due to its interaction with the threads of the lens housing; the lens can be moved linearly by rotating the lens carriage via the finger access on one of the corners of the housing, permitting it to move in both directions along the lens’ concentric axis. The lens housing and carriage were threaded with a 1.0mm pitch using a tap and lathe, respectively, which afforded the lens to move biaxially with one revolution corresponding to a 1.0mm translation. To simplify the fabrication of several carriages for different sized lenses, the design of the carriage was standardized such that only the hole size will need to vary to fit a variety of lens diameters (figure 2.15). Furthermore, for large lens displacement modifications, this lens assembly was attached to a linear bearing carriage and guide rail from McMaster-Carr (part #6723K9 and #6723K5). This facilitated the smooth and accurate linear motion required when major modifications on the optical distances had to be implemented.

Laser Housing and Base

To hold the laser module, it was contained inside its own housing and was secured using an M3 set-screw on its side (figure 2.16). Alignment between the laser and the focusing lens 2.3. Mechanical 27 was ensured by placing the laser on the same linear bearing as the focusing lens. Through this arrangement, they are assembled to share the same optical axis, effectively maintaining alignment between the laser and focusing lens even during manual distance modifications.

Figure 2.16 Laser Barrel

The drawings for each of these parts can be found in Appendix B.

2.3.3 Final Optical Fixture Design

After using the first design to validate simulation results and determine actual optical distances, a fixture was constructed with the established spacing dimensions between each component. This resulted in a more compact fixture (figure 2.17) that fits within the goal of having a portable, after-market HUD for automobiles. This subsection of the report will only detail modifications done on the first design of the fixture since the principle of operation remains the same.

Linear XY Stage

The linear XY stage from the first design was modified to be more compact. For the y-axis, the same principle is applied - a screw mechanism is used to finely translate the stage in the y direction. For the x-axis, however, the mechanism was replaced by two screws in a rectangular slot (figure 2.18). Although this alternative does not provide the same level of precision as the prior design, it does provides it with a more secure and permanent hold, ensuring that the alignment will remain even under external forces and heavy vibration. 2.3. Mechanical 28

Figure 2.17 Final Optical Fixture Design

Furthermore, to eliminate the added height from the screw head, the method to fasten the screw on the rotary bearing was changed. Instead of using a nut to lock the screw, the head of the screw was turned using a lathe so that it can be press-fitted inside the rotary bearing. This allowed for a more permanent fit that also reduced the overall height of the fixture.

Magnifying Lens

From the first optical fixture, it was determined that the magnifying lens had to be placed approximately 8mm away from the cover of the micromirror packaging. This distance was then fixed in the final design so as to eliminate the additional height associated with the adjustable feature initially included in the first fixture design. This resulted in a significant reduction in height of the complete assembly without compromising on the quality of the image.

Focusing Lens and Lens Barrel

Since the magnifying lens has been fixed, any minor adjustment to improve the focus of the image relied on the mobility of the laser module’s focusing lens. This was incorporated into the design by having two set-screws to fix the laser module: one set-screw to fix the lens, and another to fix the diode (figure 2.19). The set-screw to fix the lens is used to 2.3. Mechanical 29

Figure 2.18 Linear XY Stage secure the lens housing so that, by rotating the body of the module while the lens is fixed, the distance between the diode and lens can be finely adjusted. Once a focused image has been established, the second set-screw is used to secure the laser housing, cementing the distance between the laser diode and its focusing lens. This design allowed the HUD to remain portable without compromising on the quality of the projected image.

Base

Due to a combination of material thickness, a large cutting surface, and the inherent greasy texture of Delrin, it became difficult to clamp the material on a manual mill as it would often slip off the vice as the tool contacts the part. For this reason, the material for the base was changed to aluminum. This allowed for a much more streamlined fabrication process since no additional custom fixtures had to be manufactured to fasten the part during machining operations. Also, although the aluminum added mass to the completed product, much of that mass was concentrated at the bottom of the HUD, which added stability to the product for use. Furthermore, since continuous adjustability was no longer a factor, the linear bearings 2.3. Mechanical 30

Figure 2.19 Laser Barrel Assembly that were used in the first optical fixture were replaced with rectangular slots embedded in the base. Although adjusting the lenses was not as easy, it provided a more secure way to fasten the lenses and lasers to their proper location. Also, by removing the linear bearings, the added cost of the bearings was removed and the design was further miniaturized.

2.3.4 Complete Assembly

Once all the components were fabricated, it was assembled, along with the printed circuit boards, inside a 3D printed enclosure. This enclosure was designed to allow for continuous maintenance of the projector by providing the user an accessible, but discrete, opening in case the product requires further configuration or reprogramming. Also, since the HUD is meant to be an after-market device, its portability was an important consideration. However, the relatively large size and heavy mass of the device was limited by the optics-micromirror assembly. Therefore, the design of the outside form factor was used to counteract these effects; the outside surface of the device was modeled after the contours of a hand holding the device with a comfortable but firm grip. This resulted in a product that is both practical and aesthetically pleasing. A render of the final product can 2.4. Electronics 31 be seen in figure 2.20.

Figure 2.20 Final Product

In the course of developing a portable HUD, two mechanical fixtures were developed. The first fixture was used to practically determine the dimensions required in the optical assembly, which informed the design of the second more compact version that was ultimately used in the final prototype. The mechanical drawings and details regarding the assembly of all the parts included in the product can be found in Appendix B.

2.4 Electronics

The micromirror was controlled using an assembly of resistors, capacitors, and integrated circuits (IC) centered around a 16-bit microcontroller. This includes circuits employed for power management, microcontroller integration, high voltage amplification, laser modulation, and wireless communication via Bluetooth. This assembly of components then resulted in a custom electronic PCB, complete with all the necessary peripheral ICs, that was able to modulate laser diodes and effectively steer micromirrors using patterns of analogue voltage signals. 2.4. Electronics 32

For maintenance purposes, three separate PCBs were fabricated, each with their own function: power management, microcontroller and its peripherals, and high voltage amplific- ation. This modular design of the circuit boards was implemented to allow for individual circuit troubleshooting and modification during development. A complete bill of materials of all the electronics components used can be found in Appendix C.

2.4.1 Power Management

In order to power the microcontroller and its peripherals, several voltages had to be regulated from the device’s 5V , 1A power supply. This subsection details how the power from the supply was distributed among several IC components that each required different operating voltages. For the complete schematic of the power management circuit, please refer to figure 2.21.

Figure 2.21 Power Management Schematic 2.4. Electronics 33

2.5V Voltage Supply

A series reference from Linear Technology (LT1460) was used to provide each of the digital to analog converters (DAC) with a voltage reference of 2.5V [57]. For this application, a series reference was selected for its general characteristic of providing a higher accuracy over standard voltage regulators [58]. Although series references also typically generate a much lower current, the DAC used in the system only required 90µA[59]. In this case, since the LT1460 is able to supply up to 20mA of current on its output, it was more than suitable to act as a voltage reference for the selected DACs. Furthermore, a decoupling capacitor was attached to the input of the LT1460 to reduce the effect of a voltage surge in the input voltage, as recommended by the application notes in the LT1460 datasheet [57]. These design considerations then resulted in the accurate and relatively clean voltage reference input into the system’s set of DACs.

±5V Voltage Supply

To provide the high voltage amplifier with the necessary low positive and negative voltage supplies [60], a DC/DC converter and voltage inverter were implemented to create the +5V and −5V rail, respectively. This circuit, which was designed by [41], uses an LTC1754-5, a switch-capacitor regulator from Linear Technology, to generate a +5V rail. The LTC1754-5 is a converter capable of taking voltage inputs that range from 2.7V to 5.5V to supply a +5V output [61]. Unlike linear voltage regulators, a charge pump DC/DC converter does not exhibit a dropout voltage, or an input-output voltage differential; a charge pump is designed to boost its input voltage to its specified output by rapidly charging external capacitors, allowing it to operate within a narrow band around the desired output voltage [62]. This

quality lent itself well in the HUD since the power input to the system, or VCC , supplied a voltage level close to the desired output from the converter. Also, since it is able to operate with a maximum output current of 50mA [61], it proved to be substantially sufficient to meet the 1mA requirement of the high voltage amplifier [60] and the 200µA operating current of the −5V voltage inverter [63]. Furthermore, the −5V voltage was generated using the NCP1729, a switched capacitor 2.4. Electronics 34 voltage inverter from ON Semiconductor. This voltage inverter was implemented to convert the +5V input generated by the LTC1754-5 into a −5V output, creating the necessary voltage rail to supply the low negative voltage required by the high voltage amplifier. The NCP1729 is a charge pump voltage inverter that operates with an input voltage range of 1.15V to 5.5V , consumes 122µA of current, and permits a maximum output current of 50mA. Also, it boasts a 99% conversion efficiency, which allowed it to convert the +5V into −5V without exhibiting a significant dropout voltage. Therefore, since the output current is well above the high voltage amplifier’s current requirement, the NCP1729 was selected to be an ideal chip to supply −5V to the amplifier IC.

3.3V Voltage Supply

A 3.3V voltage regulator was included in the power-management circuit to supply 3.3V to a multitude of peripherals used in the HUD’s embedded system: the +5V charge switch- capacitor regulator, the microcontroller, three laser diodes, a bluetooth module, and three DACs. From each of these components’ datasheets, it was determined that the demand for current required to power these components totals to approximately 602mA; the +5V regulator requires 13µA to operate [61], the microcontroller has an absolute maximum input current rating of 250mA [64], approximately 100mA for each laser diode (obtained experimentally), 0.7mA for each of the three DACs [59], and 50mA for the bluetooth module and antenna [65]. This high demand for power from the 3.3V source made the maximum output current of the voltage regulator to be the key criterion in its selection process. One voltage regulator that suitably fit this criterion is the TLV1117 from Texas Instru- ments. The TLV1117 is a 3.3V fixed low-dropout voltage regulator that is able to continually supply up to 800mA of output current. It is designed to have a maximum dropout voltage of 1.3V at 800mA and is able to operate within a temperature range of −40◦ to 125◦ [66]. These features made the TLV1117 to be the ideal candidate to regulate the 3.3V rail in the HUD’s embedded system. 2.4. Electronics 35

Raw Voltage Supply

In cases where voltage noise wasn’t a concern, such as supplying power to the DAC, high voltage amplifier, and high-voltage DC-DC converter, an unregulated VCC signal rail was also included. This, in effect, took on the demand for current that would have otherwise gone through the voltage regulators, effectively improving on the overall power distribution efficiency of the overall system. After careful consideration of the peripherals used in the HUD’s embedded system, five voltage rails were generated: a 2.5V , 3.3V , +5V , −5V , and VCC . Using a set of charge-pump converters, voltage inverters, and voltage regulators, the different ICs used in the electrical design of the HUD were powered resulting in the successful operation of the HUD. To view the complete electrical schematic and bill of materials (BOM) of the power management circuit, please refer to Appendix C.

2.4.2 Microcontroller

Prior to selecting the microcontroller, all the necessary peripherals for the HUD’s embedded system were identified. This procedure assisted in generating a criterion consisting of a list of functional requirements that the microcontroller needs to allow for digital to analog conversion, digital signal modulation, and wireless communication. From this analysis, it was gathered that the microcontroller should have an operating frequency of at least 40MHz, a serial peripheral interface (SPI) module, a universal asynchronous receiver/transmitter (UART) module, and at least 6 available general purpose input/output (GPIO) pins – the 40MHz is necessary to maximize the frequency range the micromirror will be allowed to operate in, the SPI module and UART to interact with the DAC and Bluetooth, respectively, and the GPIO ports to modulate the three laser diodes. Based on these, the PIC24HJ256GP206A microcontroller was selected to be one that meets these established standards. The PIC24HJ256GP206A is a microcontroller IC from Microchip that is able to operate in a frequency range that goes up to 40MHz using its Phase Locked Loop feature. It is capable of interfacing with several serial peripherals simultaneously using the SPI, UART, and I2C protocols and has a total of 64 pins using its TQFP packaging, 51 of which can be 2.4. Electronics 36

Figure 2.22 Microcontroller Schematic mapped as GPIO ports [64]. For the complete schematic of the microcontroller, please refer to figure 2.22.

Phase Locked Loop

In order to achieve the required 40MHz operating frequency, the microcontroller’s on-chip Phase Locked Loop (PLL) had to be utilized. A PLL is a closed loop system that combines a voltage controlled oscillator with a phase comparator such that a constant phase angle is maintained relative to a reference signal. It is often used to yield a stable high-frequency signal based on a fixed low-frequency signal [67]. In the case of the HUD, the microcontroller’s Fast RC (FRC) internal oscillator was used as a reference to generate an operating frequency of approximately 40MHz (39.62MHz, precisely) from a 7.37MHz reference. External oscillators, such as crystal and RC oscillators, were also examined with the microcontroller. However, they exhibited too much sensitivity to external vibrations and occupied a significant footprint on the PCB, while the microcontroller’s internal oscillator proved suitable enough for this application. Hence, the microcontroller’s FRC internal oscillator was chosen to be the appropriate reference oscillator for the PLL. 2.4. Electronics 37

Also, the settings to configure the PLL were set using the microcontroller’s firmware. Before entering the main body of the system’s software, the configuration for each of the microcontroller’s features were initialized. For the PLL, the prescaler, postscaler and feedback divisor need to be set according to

 M  FIN × N ×N F = 1 2 CY 2

where FCY denotes the resulting output frequency, FIN the reference frequency, M the

feedback divisor, and N1 and N2 as the PLL’s prescale and postscale factors, respectively [64]. In the case of the HUD system’s operating frequency, the FRC’s frequency of 7.37MHz

was used as the reference frequency (FIN ), which was scaled using a feedback divisor of 43, a prescale factor of 2, and a postscale factor of 2. This resulted in the microcontroller’s operating frequency of 39.62MHz, which closely approximates, and is considered to be running at, its maximum frequency of 40MHz.

Serial Peripheral Interface

Another feature that the PIC24HJ256GP206A offers is the ability to communicate with serial-enabled peripherals via a Serial Peripheral Interface, or SPI. SPI is a synchronous serial data communication protocol that allows for both transmission and reception of sequential serial data to and from SPI-enabled ICs. It follows a master-slave relationship between the microcontroller and its peripherals, where the master is responsible in generating the clock signal that each slave device synchronizes to. This type of configuration also permits the connection of several slaves to one master using four lines of communication: Serial Data In (SDI), Serial Data Out (SDO)3, Serial Clock (SCK), and Slave Select (SS) [68]. To interface multiple slaves with a single master, there are two possible configurations: using individual SS pins (figure 2.23) or through a daisy-chain arrangement (figure 2.24). In both of these configurations, the SCK bus is generated by the master and is shared by all the slave devices. Also, for both setups, the master and slave transmit serial data through

3SDI and SDO are sometimes referred to as Master-In Slave-Out (MISO) and Master-Out Slave-In (MOSI), respectively. For the purpose of this report, they will be referred to as SDO and SDI to maintain consistency with Microchip’s, the microcontroller manufacturer’s, vocabulary. 2.4. Electronics 38 their respective SDO pins and receive data into their SDI pins.

Figure 2.23 Individual SS Pin SPI Configuration [68]

Figure 2.24 Daisy Chain SPI Configuration [68]

The key difference between the two arrangements is how the serial data is distributed among each of the slaves. In the individual SS pin configuration, each slave device has its SS pin connected to its own SS pin on the master. Functionally, for a specific slave to transmit or receive data, the master must activate the chip by enabling it through its corresponding SS pin. For example, in figure 2.23, if Slave 1 is the only slave that requires serial data, SS1 will be enabled during transmission, while the SS2 to SSn pins are disabled [64]. Although this setup was initially considered for the DACs, it was observed that unnecessary processor cycles were being expended on activating each individual chip in between transmissions. 2.4. Electronics 39

This resulted in an inefficient communications cycle that severely limited the analog voltage output frequency of the DACs. To resolve this issue of inefficiency, a daisy chain configuration was implemented to network three DAC slaves to a master, the PIC microcontroller. This setup functions by segmenting the serial data transmission bus from the microcontroller into several line fragments that are interlinked using the SDI and SDO pins of sequentially-assembled peripherals (figure 2.24). In the daisy chain arrangement, serial data is distributed among its peripherals by having excess serial data that enter the SDI pin overflow out of the same peripheral’s SDO pin using a First-In, First Out (FIFO) protocol. This overflow data then enters the SDI port of the subsequent peripheral in the sequence wherein the cycle repeats until it reaches the last slave, Slave n. Following Slave n, any overflow data is then transmitted back into the master’s SDI pin. The amount of serial data that remain in each of these peripherals depends on the specified resolution of the particular IC [59]. For example, 16-bit DACs will only retain 16-bits of serial data, effectively pushing any additional bits out through its SDO pin. Therefore, the procedure to communicate with the DACs was further streamlined using a daisy chain by allowing the microcontroller to send data to the complete array of DACs sequentially without the constant interruption of enabling/disabling of the SS pins of each DAC. For more details regarding the procedure of operation for the DACs, please refer to section 2.4.3. Furthermore, in order for this procedure to work, all of the slaves need to be enabled simultaneously. Hence, only one SS pin from the master is required. This reduced the required GPIO pins to operate three DACs from three to one and eliminated unnecessary traces on the PCB, mitigating any issues regarding signal interference that may arise due to the mixed signal operation of the DAC [69]. Much like the PLL, the settings for the SPI, including setting the desired SPI frequency, can be configured using the microcontroller’s firmware. To set the SPI operating frequency, the module’s primary and secondary prescalers were set according to

F F = CY SPI P × S 2.4. Electronics 40

where FSPI denotes the resulting SPI frequency, P the primary prescaler, S the secondary prescaler, and FCY the microcontroller’s operating frequency [64]. In the case of the HUD system, the primary and secondary prescalers were set at four and one, respectively, which resulted in the SPI operating at the microcontroller’s maximum allowable SPI frequency of 10MHz [64]. This value was selected experimentally based on the quality of the image from the projector, resulting in an display with minimal noticeable flicker. For a complete list of the microcontroller’s SPI configuration parameters, please refer to Appendix D.

Universal Asynchronous Receiver/Transmitter

The selected PIC microcontroller was also equipped with a Universal Asynchronous Re- ceiver/Transmitter (UART) to permit communication between the microcontroller and a Bluetooth module and antenna. UART is a serial communications protocol, similar to SPI, that enables the microcontroller to send serial data to other peripherals and devices. However, unlike SPI, UART does not require a synchronized clock; it is asynchronous and merely needs the speed, or baud rate, between the microcontroller and the peripheral to be the same. It is typically used as a communication line between two devices or peripherals, and it only requires two buses, receive (Rx) and transmit (Tx), to interact [64]. For the HUD’s embedded system, the UART protocol was used to permit communication between the microcontroller and a Bluetooth module. Electronically, the microcontroller and the Bluetooth module were connected by wiring the Rx pin of the microcontroller to the Tx pin of the Bluetooth module, and the Tx pin of the microcontroller to the Rx pin of the Bluetooth module. This allows the Bluetooth module to transmit data directly into the microcontroller without requiring additional procedures, such as the slave select or synchronous clock operations present in the SPI protocol. This received data is then stored in the U2RXREG register, which can then be read by the microcontroller’s embedded software. For more details on how this data is used in the HUD’s operation, please refer to section 2.5. Furthermore, although the Bluetooth module will only be sending data into the micro- controller, the Rx pin of the microcontroller was still connected to the Bluetooth module’s Tx pin so that the microcontroller does not have any floating pins. Floating pins are pins 2.4. Electronics 41 that are internally configured to be inputs but are not connected to any peripheral or resistor. For best practices, these need to be minimized because their indeterminate state introduces uncertainty which may affect the functionality of the embedded system; readings from a floating pin will unpredictably vary as either a 1 or a 0, which the software may erroneously interpret as a change in sensor or serial data readings. Also, floating pins may store low to intermediate voltage levels, which could act as unnecessary current drains for the microcontroller [70]. For more information regarding the operation of the Bluetooth wireless communication design, please refer to section 2.4.6. In configuring the settings for the UART protocol, a key factor is the UART’s assigned baud rate - the baud rate between two UART-enabled devices must exhibit the same rate in order to communicate with each other [71]. With the PIC24HJ256GP206A microcontroller, this baud rate can be set according to

F BaudRate = CY 16 × (U2BRG + 1) where U2BRG denotes the special function register (SFR) dedicated to setting the UART’s baud rate [64]. For the purpose of the HUD, the U2BRG register was set to 259, which resulted to a baud rate of approximately 9600 (9615, precisely4). This baud rate was selected based on a list of standard rates for consumer products, and, although there are several higher rates available, 9600 proved to be sufficient in communicating with smartphones during testing. Also, by selecting a lower baud rate, the HUD will be able to interact with a wider variety of external devices, such as smartphones and GPS, especially devices that can only generate a maximum baud rate of 9600. To see the complete configuration information for the microcontroller’s UART module, please refer to Appendix D.

General Purpose Input/Output

To rapidly modulate the laser during operation, each of the lasers used in the HUD was paired with a general purpose input/output (GPIO) pin. These pins were connected to

4Due to the discrete nature of the U2BRG register, the actual baud rate may never be precisely equal to the desired baud rate 2.4. Electronics 42 digital modulation circuits (detailed in section 2.4.4) that toggled individual laser modules at a high frequency in order to turn the laser on for visible vectors, and off for transport vectors5. This gives the HUD the necessary versatility that allow it to draw more complex graphics, including non-continuous vectors such as an exclamation point (figure 2.25).

Figure 2.25 Continuous (left) vs. Non-Continuous Vector (right)

Relative to the other functions of the microcontroller, the settings for the GPIO ports are relatively simple. Each of the designated modulating pins merely needs to be set as output pins in the microcontroller’s initialization by setting their corresponding TRIS registers to 0. This gives each of these pins the ability to regulate a 3.3V , 4mA output. Once the list of peripherals was set, a microcontroller was chosen based on the criteria established from the requirements of each of the system’s ICs. This resulted in the selection of the PIC24HJ256GP206A microcontroller as the suitably viable candidate that met all the functional requirements of the HUD’s complete embedded system.

2.4.3 Digital to Analog Converter

In order to rapidly steer the micromirror, analog voltages were applied to each of the micromirror’s actuators, with the level of the voltage dictating the stroke of each actuator. This was achieved by pairing each of them with a channel from a digital to analog converter so

5Visible vectors are defined as perceivable vector-traced lines that constitute the image displayed on the HUD, such as the lines that construct an arrow or number, whereas transport vectors are invisible paths that allow the laser to travel between visible vectors. 2.4. Electronics 43 that digital signals from the microcontroller can be translated into the micromirror’s rotation angle. To view the schematic of how the DACs were interfaced with the microcontroller, please refer to figure 2.26.

Figure 2.26 DAC Schematic

For the selection process of the digital to analog converter (DAC), several parameters were taken into consideration. Among them are the DAC’s accuracy and transient response. To see the complete selection chart for the DAC, please refer to Appendix C.4.

Accuracy

Typically, a DAC’s absolute accuracy can be measured using three fundamental kinds of error: offset, gain, and nonlinearity. In most applications, offset and gain errors can be addressed using simple end-point calibration procedures in the system design. Nonlinearity errors, however, require a more complex approach [72][73]. Therefore, before exploring solutions to compensate for nonlinearity, an attempt to minimize them in the DAC selection process was performed. One property that is commonly used to characterize nonlinearity is a DAC’s integral nonlinearity (INL) error. It is an attribute that describes the deviation of the DAC’s actual transfer function from linearity and is calculated to be the summation of voltage deviations at each voltage step from 0V to the DAC’s maximum voltage. It is measured in least-significant 2.4. Electronics 44 bit (LSB) units, with one LSB unit equivalent to the DAC’s voltage step size [73]. Hence, the selection criterion for the DAC’s accuracy was based on minimizing its INL error.

Transient Response

Since the voltages applied to the micromirror’s actuators will be transmitted rapidly, the transient response parameters of the DAC were also evaluated. The transient behaviour of a DAC is largely governed by two properties: glitch and slew rate. Glitch is defined as the voltage overshoot that occurs after a major transition in voltage, while slew rate refers to the DAC’s maximum rate of change as it transitions from one analog output to another [74]. Ideally, the selected DAC should have the lowest glitch impulse while also having the fastest slew rate. However, based on the DACs that were assessed (Appendix C.4), the relationship between these two properties often presented a conflict: a faster slew rate generally corresponded to a larger glitch value. Therefore, the selection criterion on transient response was based on seeking a proper balance between the two parameters.

The AD5684

Based on these two criteria, and the ones outlined in Appendix C.4, the AD5684 from Analog Devices proved to be an appropriate solution to translate digital signals from the microcontroller to analog voltages for the micromirror’s actuators. The AD5684 is a four- channel DAC that boasts highly competitive features, including a maximum INL of ±1LSB, 0.8V/µs slew rate, and a 0.5nV -sec glitch impulse. It is able to operate up to a maximum SPI clock frequency of 50MHz, which is suitably higher than the microcontroller’s operating SPI frequency of 10MHz (Section 2.4.2) and offers a Load DAC (LDAC) feature. Also, to meet the SPI configuration requirements established in section 2.4.2, it possesses the ability to function well in a daisy chain configuration [59]. These specifications and features made the AD5684 an attractive solution as the HUD’s DAC. Before implementing the AD5684 into the system, one of the features that was verified was its INL error. Theoretically, the voltage output of the DAC based on a corresponding 2.4. Electronics 45

Figure 2.27 Voltage Output Verification digital signal was predicted using the linear transfer function

 D  V = V × Gain OUT REF 2N

where VREF denotes the DAC’s reference voltage, Gain the gain of the DAC’s internal output amplifier, D the decimal equivalent of the digital signal loaded into the DAC, and N the resolution of the DAC [59]. For this application, the values for the transfer function and the IC were set at 2.5V for VREF , 2 for the Gain, and 12 for N. This resulted in the linear relationship that was subsequently verified on the PCB. The comparison between the two results is shown in figure 2.27. From the chart shown in figure 2.27, it can be observed that the actual voltage output tracks the linear theoretical voltage output fairly well. In fact, the INL was calculated to be less than 0.5LSB. This means that the output voltage of the AD5684 can be modeled linearly and estimated accurately, which consequently simplified the software design and calibration of the HUD. 2.4. Electronics 46

Electronically, the AD5684 was used as the intermediary step in translating digital signals into analog voltages. Each of these four-channel DACs was paired with a micromirror, with each channel in the IC associated with an electrostatic actuator. Since three micromirrors were used, three AD5684s were connected using a daisy chain setup. Figure 2.28 presents a version of the daisy-chain arrangement that has been modified to fit the feature-set and functionality of the AD5684 and microcontroller, the PIC24HJ256GP206A. Compared to the general daisy chain SPI configuration in figure 2.24, this diagram is identical with the exception of two key differences: the substitution of the SS pin with a SYNC pin, and the addition of an LDAC pin on the DACs. Although the terminology may be different between the SS and SYNC pins, functionally, they are the same; once triggered, both the SS and SYNC pins mark the beginning of transmission for the DAC. Typically, SYNC is only used for daisy chain enabled devices. However, this isn’t always the case and the vocabulary choice can vary depending on the manufacturer. The other feature that is unique to some DACs, including this one, is the presence of the LDAC function. The LDAC is a feature present in some multi-channel DACs that allow them to release several analog voltages through multiple channels simultaneously. This is done by having each DAC store the received serial data for each channel until the LDAC pin has been activated. Once enabled, the voltages that correspond to the stored serial data are released through the appropriate channels [59]. In the case of the HUD’s projector, this feature allowed the micromirrors to rotate accurately, since each of their fingers were actuated instantaneously for each rotation. Furthermore, much like the microcontroller, the settings for each of the DACs needed to be configured within its own firmware. This is done by transmitting the command bits according to figure 2.29 to each DAC prior to executing the system’s operating software. The main purpose of these commands is to toggle features offered in the DAC, including the daisy chain and readback features. These command bits are also used to individually address each of the channels of the AD5684, which is included in the software code shown in Appendix D. 2.4. Electronics 47

Figure 2.28 AD5684 Configuration

2.4.4 Laser Modulation and Driver

In order to display more complex images that include both visible and transport vectors, each of the laser modules in the projector were rapidly modulated; the lasers were toggled on for visible vectors, and toggled off for transport vectors. These modulation signals were generated using digital signals from the system’s microcontroller, which outputs either a HIGH (3.3V ) or LOW (0V ) signal on its GPIO pins. However, the microcontroller used in the projector is severely limited in its maximum current output; the maximum current a GPIO port on the PIC24HJ256GP206A can supply is limited to 4mA [64]. This was insufficient to supplement the 100mA of current required to power each laser module. Therefore, an intermediate buffer circuit with the purpose of deviating the high load current of each laser module away from the microcontroller was implemented. This load switch application was achieved by connecting a P-channel MOSFET IC to each of the laser’s corresponding GPIO pin on the microcontroller [75]. Using the circuit shown in figure 2.30, the low-current voltage signals from the microcontroller’s assigned GPIO pins (pins RG12, RG0, and RF1) were each connected to the base pin of a bipolar-junction transistor (BJT). This, in turn, allowed the microcontroller to modulate the MOSFET’s gate, effectively trafficking the power in and out of each laser module. This successfully resulted in a laser modulation circuit that is capable of responsively toggling the laser module at a fairly high frequency. In this circuit design, a number of safety precautions were implemented to minimize catastrophic failures during development and operation. For instance, instead of connecting 2.4. Electronics 48

Figure 2.29 AD5684 Input Shift Register Contents[59] the microcontroller’s GPIO pins directly to the MOSFET’s gate pin, a BJT is implemented to create a safety buffer between the MOSFET and the microcontroller. This created a sacrificial redundancy in the form of the BJT in case an unintended short in the circuit occurs during fabrication or testing. Furthermore, a 10kΩ resistor was placed in series with each of the the GPIO pins from the microcontroller and the raw voltage supply (VCC ) to limit the current through each line. By adding these resistors, the current drawn from the microcontroller and power supply is capped at a safe 330µA. These factors, then, allowed for the successful and robust implementation of a digital modulation circuit for each laser module in the HUD projector.

2.4.5 High Voltage Amplifier

Since the actuators on the micromirror are steered using voltages that range from 0V to 200V , the analog voltages from the 5V DACs had to be amplified. This was done using the schematic shown in figure 2.31, where a circuit that includes a high voltage amplifier and a high-voltage DC-DC converter is presented. 2.4. Electronics 49

Figure 2.30 Load Switch Circuit for Laser Modulation6

To achieve the necessary gain to amplify the DACs’ voltage, the HV254 high voltage amplifier array from Supertex Inc. was used. The HV254 is a 32-channel amplifier with a fixed gain of 50V/V and a maximum output voltage of 250V . It guarantees a rapid slew rate of 3V/µs and functions at a low operating current of 45µA per channel [60]. This low operating current provides the necessary precautionary measure by limiting the current entering the micromirror well below its maximum allowable current, even in cases where the actuators may contact the fixed fingers and form a short circuit. These features made the HV254 a uniquely ideal solution for amplifying the DAC voltages to the necessary levels to steer the micromirror. The HV254 is powered using multiple levels of voltages: two low-voltage supplies, −5V and +5V , are delivered using voltage regulators and voltage inverters, as detailed in section 2.4.1, and a high-voltage supply, 200V , is provided using a high-voltage DC-DC Converter, the 5SM200S. The 5SM200s is an unregulated DC-DC Converter from PICO Electronics that is capable of converting an input of 5V into 200V and supply a maximum load current 2.4. Electronics 50

Figure 2.31 High Voltage Amplifier Circuit of 6.25mA. Since the 5SM200S is unregulated, the voltage output varies depending on the load it is paired with; a lower resistive load may even result in a voltage output greater than 250V . This stems from a much higher current draw than the converter’s maximum load current due to the high voltage supply and low resistance value of the load. Therefore, to make sure that the load current stays under the maximum load current of the converter, a 280kΩ resistor was placed between ground and the output. This resistor, in effect, acts as a pre-load to the DC-DC converter, which guarantees that the load current leaving the 5SM200S stays under 6.25mA. Also, as per [76], a 0.1µF , 500V capacitor was installed in parallel with the load to prevent a voltage surge during start-up and operation. This ensures the safety of the 5SM200S under the HUD’s normal operating conditions. These procedures, then, resulted in the successful amplification of the voltage signals from the DACs. 2.4. Electronics 51

2.4.6 Wireless Communication

In order for the HUD to communicate with external devices, it was equipped with a wireless antenna and module, the RN42. The RN42 is a Bluetooth data module from Roving Networks that allows embedded systems to transmit and receive data to and from other Bluetooth- enabled devices. It is capable of operating within a wide range of discrete bandwidths, from 1200 bps to 921 Kbps, and connects to a microcontroller using a simple UART interconnect (figure 2.32) [65]. The successful implementation of these features, then, allowed the HUD projector to successfully interact with other wireless handheld devices, specifically with an Android-enabled smartphone.

Figure 2.32 RN42 Bluetooth Schematic using a UART interface

As shown in the schematic in figure 2.32, several hardware considerations were accounted for to effectively implement the Bluetooth module in the HUD’s embedded system. Apart from the UART’s required receiver/transmitter interconnect outlined in section 2.4.2, a couple of LEDs and a reset button were included to make use of the RN42’s indicator and factory reset function, respectively. To display the status of the system’s Bluetooth module, indicator lights were installed: a blue LED light was connected to the RN42’s GPIO2 pin, and a green LED light was 2.4. Electronics 52

connected to the module’s GPIO5 pin. Each of these pins indicate the various statuses the module can be on, with the GPIO2 signifying the RN42’s status and the GPIO5 denoting Bluetooth connection status [65]. These indicators effectively provide the user with the proper visual feedback, hence improving on the product’s overall physical user interface. Furthermore, in some cases where the RN42 has been misconfigured, the only way to troubleshoot the module is to reset it to its factory default settings. This is done by toggling its GPIO4 pin in a low, high, low, high sequence with a one second interval between each transition [65]. To simplify this operation, a surface-mounted reset switch was added that links the GPIO4 pin to the 3.3V source when engaged and to 0V when disengaged. This significantly improved the troubleshooting procedure for the device during product development and fabrication. Much like the AD5684, the settings for the RN42 module are configured through its firmware. However, instead of modifying its parameters using signals from the microcontroller, the RN42 is set up using an external Bluetooth-enabled device. With a Serial Port Profile (SPP) communication software, the RN42 was fixed to match the established UART baud rate of 9600 bps (section 2.4.2) with flow control signals disabled7. These settings were adjusted using Bluetooth SPP Pro, a smartphone application available for Android-based devices. With this same software, a set of buttons were configured to send specific serial data signals to the HUD’s embedded system. The structure of the communications protocol is set such that each button on a smartphone, when engaged, would immediately send a signal to the microcontroller, which changes the state of one of the micromirror’s total vector path. In the case of the prototype detailed herein, the buttons were set to change the direction of the arrow being displayed (figure 2.33). More details on this protocol can be found in section 2.5.2. After establishing the desired features of the HUD, each of the components included in its embedded system were carefully assessed. Although other qualifications were examined, much of the criteria throughout centered around generating clean analog signals in the

7Although electronically connected, the CTS and RTS flow control signals were disabled in this application because of the unnecessary complexity it introduced to the software algorithm. 2.5. Software and Microcontroller Firmware 53

Figure 2.33 Smartphone Bluetooth SPP Software with the Output Image midst of a mixed-signal PCB. This resulted in a fully integrated PCB layout and electrical schematic that successfully steered the three micromirrors to produce a bright, high-contrast image.

2.5 Software and Microcontroller Firmware

Programmed into the HUD’s microcontroller is the system’s firmware. This firmware functions to mediate the interaction between the peripheral ICs around the system such that signals received wirelessly on the Bluetooth module translate into the transmission of the necessary analog voltages to steer the micromirror. However, even before the firmware is programmed, the path used to navigate the micromirror’s rotation was outlined using a set of digital signals generated through a look-up table.

2.5.1 The Look-Up Table

To set the micromirror path configurations, a look-up table was charted during the develop- ment of [41]. In this paper, it was found that distortions were present in the image when the micromirror is used in a projector application. The look-up table (LUT) was formed to 2.5. Software and Microcontroller Firmware 54 compensate for these distortions, since a complex, non-linear response was found between the micromirror’s rotation and the applied voltages on its actuators. This was then used to identify the corresponding analog voltages for each specific rotation angle of the micromirror, thus allowing for a fairly precise and predictable relationship between the two variables [41]. The procedure to form the list of the necessary analog voltages used to guide each actuator through each rotation centered around the use of a custom software developed by [41] and [42]. With this tool, the user can draw a vector graphic on a Microsoft Excel plot, which then translates it into a sequential list of analog voltages for each actuator to follow. This list of voltages, then, consequently rotates the micromirror according to the originally drawn vector. Although this design worked well for each of their applications, some modifications and additional features were incorporated into the software to fit the current design of the HUD. In the initial iteration of the LUT software, there was no feature assigned to laser modulation. The projector developed by [41] was only capable of drawing continuous visible vectors and so there was no need to incorporate laser modulation for transport vectors in the software. Therefore, to allow users to display more complex images that include separation gaps between each visible trace, a laser modulation feature was added to the LUT software’s design. Furthermore, since the microcontroller will be sending digital signals to the DAC, the analog voltages that result from the software’s initial design had to be translated into a more convenient format. In this case, the analog voltages that were generated by the initial design were translated into the appropriate hexadecimal value that matches its equivalent analog voltage in the revised version of the software. This was done by including a macro that automatically translates the list of analog voltage values for each actuator into its hexadecimal counterpart. This macro, then, subsequently segmented the data into files that separated each list according to their designated actuator. This additional function in the software effectively assisted in bridging the gap between the initial design of the software and programming the microcontroller’s firmware, further simplifying the HUD’s software user interface. 2.5. Software and Microcontroller Firmware 55

2.5.2 Microcontroller Firmware

The firmware used to facilitate all of the inputs from and outputs to the different IC peripherals of the HUD’s system was executed using the PIC24HJ256GP206A microcontroller (section 2.4.2). This software was programmed such that signals received wirelessly through the Bluetooth module would direct the microcontroller to parse the image data contained within the firmware between the corresponding channels for each actuator. Consequently, this allowed for the precise modulation of each laser module and accurate transmission of appropriate serial data into the corresponding DACs. This procedure is illustrated in the software code shown in figure 2.34.

Figure 2.34 Microcontroller Firmware Code

Before entering the main function of the code shown in figure 2.34, a set of 4 × 512 arrays containing vector image data were created. Each of these arrays hold a series of 8-bit values that were generated using the LUT software detailed in section 2.5.1. These arrays are formed as sequential lists of digital signals transmitted to the DACs to guide the micromirror’s 4 actuators through 512 different dwelling points. In reference to the code in figure 2.34, they were initialized to contain directions to draw vectors for a left 2.5. Software and Microcontroller Firmware 56 arrow (LARROW), right arrow (RARROW), forward arrow (FARROW), an exclamation mark (NOTIFY), and two separate digits (TWONUM). To account for visible and transport vectors, laser modulation is done using arrays of 512 variables that were each paired with a designated image array; TWONUMLASER, for example, is used to toggle the laser assigned to display the two digits, while the NOTIFYLASER is used to toggle the laser for the exclamation mark. From figure 2.34, it can be observed that a majority of the system’s operation is contained within a double-nested for-loop. The outside loop uses the pointer i to point and move through the 512 individual dwelling points in the array, while the inside loop uses the pointer k to address the four distinct channels within the three DACs. Since each iteration of the outside for-loop corresponds to a dwelling point, this loop was used to set whether a vector connecting two subsequent dwelling points is a transport or visible vector. This information is pulled from the laser modulation arrays, which contain a series of boolean values that dictate a LOW, or 0, for a visible vector and a HIGH, or 1, for a transport vector. In this case, the laser is modulated by setting the variables LASER1, LASER2, and LASER3 as a 1 or 0, which consequently turn each corresponding laser in the projector off or on, respectively. The inside for-loop functions mainly to parse the digital signals contained in the image arrays to their allocated DAC channel. Within this loop, the pointer k moves through each image array to independently address the four values required to position the micromirror to a specific angle of rotation. This is done by sending three 8-bit data-words sequentially using the SPIwrite subroutine in figure 2.35, with each of the data-words containing bits that match the DAC’s input register requirements (figure 2.36). This resulted in the accurate and precise transmission of analog voltage outputs to each of the actuators for all three micromirrors. Furthermore, since the three of the DACs that were used operate under a daisy chain configuration, the overflow of data is achieved by transmitting 72 bits of serial data to a series of three AD5684 DACs that each hold 24-bits, including data, command, and address bits. This decidedly fills all of the bits required in all of the DACs’ input registers, resulting in the simultaneous release of voltages in each of the DACs’ channels To accommodate for signals received wirelessly from external devices, the ReceivedChar 2.5. Software and Microcontroller Firmware 57

Figure 2.35 SPI Function

Figure 2.36 AD5684 Command Bits and Addressing Mode [59] variable was created as a buffer to hold the 8-bit serial data in the microcontroller’s UART register, U2RXREG. For the purpose of this prototype, this signal allowed smartphones to change the direction of the arrow being displayed by the HUD using a Bluetooth connection. This happens inside the inner for-loop, as each iteration checks the ReceivedChar buffer for a trigger to change to a suitable vector image. For the full software code used in the HUD, please refer to Appendix D. Once the hardware components of the HUD were assembled, the system’s software was designed to improve the product’s overall user experience and to integrate all of the peripherals used in its electrical schematic. First, by providing the user with a graphical 2.5. Software and Microcontroller Firmware 58 interface to draw his/her desired vector image using the updated LUT, the product’s ease of use was significantly improved. Furthermore, in order for the embedded system to function as a projector, a structure was programmed into the microcontroller which fittingly interfaced all of its peripherals, resulting in the complete and successful operation of the HUD prototype. Chapter 3

Display Performance

Once all the components of the HUD have been assembled, the visual performance of the product was improved through an iterative trial and error process. In this procedure, a number of factors were adjusted, including its versatility, image brightness, and image quality, which resulted in a compact HUD projector capable of displaying bright and even images with minimal flickering.

3.1 Controls

One of the features that was improved upon was the HUD’s uneven brightness distribution. In the original design of the projector found in [41], a scan speed control method (SSCM) was selected as the open loop control strategy to maneuver the rotation of the micromirror. This approach was used to mitigate the distortion and flickering in the image by increasing the density of dwelling points at regions where the scanned laser approaches a sudden change in direction [41]. However, this uneven density distribution of dwelling points also resulted in images that exhibited significantly brighter vectors around curves and corners. Therefore, a different control strategy was implemented to achieve more consistency in the brightness of the overall projected image. To generate an image with a more uniform brightness, the spacing between each pair of dwelling points, or the vector length between dwelling points, was made equal. Although this method was briefly explored in [41], the results that were presented displayed some distortion

59 3.2. Versatility 60 due to the ringing that occurred after a sudden change in the scanned laser’s direction. This issue was addressed in this revision of the design by minimizing the distance between each dwelling point. Although the resulting image is, in effect, smaller than what the SSCM produced, it eliminated drastic voltage changes that, in the previous design, occurred around curves or corners. Also, since the design of the magnifying optics was enhanced over the previous design, the size of the image was not a cause for concern. Therefore, through a rigorous trial and error process, a distance of approximately 0.002 units1 was determined to be one that gives a good balance of clarity2, size, and brightness.

3.2 Versatility

Another measure that was used to improve the HUD’s performance was its versatility, or the total number of images it can store and display, which was primarily done by maintaining an efficient use of the device’s memory. To allow the microcontroller immediate access to a vector image’s data points, the image arrays were stored in the HUD’s direct program memory. Each image array consists of 512 data points that each contain five 8-bit integers, four for actuator positioning and one for laser modulation, adding up to a total of 20.48KB of data per array. However, since the selected microcontroller, the PIC24HJ256GP206A, is limited to only 256KB of program storage capacity, the method to store images in the device’s memory had to be streamlined. This issue of versatility was resolved by standardizing the vector path for some of the images displayed by the projector. One of the images that the HUD prototype displays is a two-digit number that is meant to represent the potential application for speedometer readings or GPS distance information. If individual image arrays were created for the 100 different permutations of numerical values, a total storage capacity of 2MB of memory would be required to store the numbers alone. Hence, rather than creating individual image arrays for each combination of numbers, a universal trace path for this particular vector image was established. The path, as shown in figure 3.1, starts with visible vector 1 and follows

1The size of each unit is measured based on a full image plane composed of 10 × 10 units. 2Clarity, in this case, is defined as an objective visual assessment of distortion present in the image. 3.2. Versatility 61 each of the arrows in the figure sequentially until, in the case of a two-digit display, the 14th visible vector is drawn. Each permutation of numerical values are then varied by toggling the laser according to which portion of the image the scanned laser is in. For example, if the number 90 is required, visible vectors 1 and 8 will be used as transport vectors by turning the laser off, keeping the laser on for the other vectors in the rest of the display. This established standard for the vector path then effectively eliminated the need for micromirror positioning data for each individual numerical combination. Instead, only information on the laser modulation for each digit were stored in the device’s program memory, reducing the required capacity for each image array from 2.05MB to 20.98KB. This resulting image from the projector can be seen in figure (figure 3.2).

Figure 3.1 Vector Trace Path for Two-Digit Numerical Display

Figure 3.2 Resulting Display of the Vector Trace Path for Two-Digit Numerical Display

Furthermore, with only a few minor adjustments, this method of display should also 3.3. Final Product 62 be capable of displaying more characters. However, due to the limitations of the current generation of the micromirror, the projector is not yet able to visibly display more than two characters. In section 4, a solution is proposed where this approach may be applicable.

3.3 Final Product

After the performance of the HUD was adjusted for versatility, brightness and quality, the complete product was evaluated on its overall design. The result is a physically compact aftermarket HUD that measures 170mm × 144mm × 65mm and is capable of projecting bright, high-contrast images on a transparent screen. The resulting physical model of the HUD has been included in figure 3.3, and the resulting display is shown in figure 3.4.

Figure 3.3 Physical Prototype 3.3. Final Product 63

Figure 3.4 Final HUD Screen

3.3.1 Directions

To assist in driver navigation, the HUD was designed to display a variety of different arrows. For instance, a left arrow projected by the HUD is shown in figure 3.5, and a right arrow in figure 3.6.

Figure 3.5 Left Arrow 3.3. Final Product 64

Figure 3.6 Right Arrow

3.3.2 Notifications

In order to test the final product’s capability, several notification geometries were tested. Included in figures 3.7, 3.8, and 3.9 are possible contours that may be used to notify the driver of sudden danger, vehicle malfunction, and mail, respectively.

Figure 3.7 Danger

Once the prototype was finished, the performance of the product was assessed based on a criterion around its display quality and versatility. The display quality was adjusted and 3.3. Final Product 65

Figure 3.8 Exclamation Mark

Figure 3.9 Mail improved upon by modifying the controls system of the software, while the versatility was increased through a more streamlined software logic. These enhancements then contributed significantly to the successful operation of a portable and competitive aftermarket automotive HUD. Chapter 4

Conclusion and Recommendations

Prior to proceeding with the design and development of the automotive HUD, a criteria informed by a benchmark analysis of the market was established. Namely, the automotive HUD was to be designed to address issues regarding screen placement, price, versatility, and portability that were present in other consumer level HUDs. To ease the product more naturally into a driver’s routine, the HUD was designed to be placed within a comfortable region in the user’s field of view - just below his/her line of sight. After a careful mechanical design and fabrication process, the resulting form factor of the HUD allowed it to be laid flat on a car’s dashboard, with its weight distribution designed to secure its placement during operation. This gave the final design of the automotive HUD a competitive advantage over some consumer HUDs by improving upon their physical user-machine interface. Also, in order to advance the final product closer to commercialization, some consideration was placed on maximizing the HUD’s economic value. Although there was a firm criterion on the HUD’s target cost, each of the components, especially parts in its optical assembly, were carefully selected based on reducing overall cost without compromising on the product’s performance; the significant cost savings incurred during the development of the prototype did not deter it from displaying a bright, yet unobtrusive, image on the user’s windscreen, thus maintaining the product’s ability to compete on the basis of both quality and economic value. Moreover, to address the issue of versatility, the HUD permitted the reconfiguration of

66 4.1. Recommendations 67 the displayed images. Due to the modular structure of its embedded system’s firmware, the images projected on the HUD’s screen can be altered by the user through a simple software update. This allows him/her to modify the aesthetic or settings of the display according to his/her personal preference for usability and comfort. Lastly, since the purpose of the product was to provide consumers with an aftermarket alternative to automotive HUDs, the portability of its form factor was also accounted for. Initially, the design for portability was approached by miniaturizing the projector as much as possible. However, due to the distances required for the optical assembly, the size was severely constricted. Thus, portability was achieved by focusing on designing the product’s exterior contours. This resulted in an aftermarket automotive HUD that, despite its relatively large form factor, provides a secure and comfortable grip for the user to hold and transport the product. Once all of these considerations were implemented, an aftermarket automotive HUD that presents a strong competitive advantage over other commercially available automotive HUDs was developed. Apart from the features discussed previously, the final product is also one that operates at a relatively low power and is capable of wireless communication with an external device. These make the end-product an attractive solution for improving safety for drivers in standard consumer-grade automobiles.

4.1 Recommendations

If the product is pursued further, a list of recommended improvements have been included. Although some recommendations were mentioned briefly throughout the body of the report, the following should be prioritized to advance the product closer towards commercialization. For the next revision of the product, the micromirror used by the projector should be altered to have a more robust mechanical structure. One of the major limiting factors that constrain the current projector’s functionality is its micromirror; the micromirror used in this generation of the product displays significant ringing when rigorously steered at a high frequency. With stronger actuators, this apparent ringing would be mitigated, allowing the micromirror to operate at a much faster speed. This would result in a projector capable of 4.1. Recommendations 68 displaying more complex images with less flicker. Also, since the microcontroller used in the design discussed herein was selected to cater to the product’s specific micromirror, the embedded system of the HUD would need to be revised to accommodate for a higher operating frequency. Although the rest of the electrical peripherals can remain, the electrical schematic for the system would need to be changed according to the layout of the new microcontroller. Furthermore, the selection criteria for the new microcontroller should also be modified to appropriately match the capacity of the new micromirror. Moreover, due to the limitations presented by manual machining operations and the limited availability of standard lenses, the size of the final product is comparatively larger than the other automotive HUD examined in Chapter 1, the Garmin HUD. This can be significantly improved if access to micromachining for fabricating custom lenses and housings is made available. Therefore, for the next iteration of the product, the mechanical and optical components should be re-examined to further miniaturize the automotive HUD. Finally, although the primary use of the final product is for an automotive HUD, other applications should be explored to expand its application as a handheld projector for transparent displays. Other applications may include store-front displays, advertising, and art exhibits. This would help extend the product’s reach, improving its chances of being a successful HUD. Bibliography

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74 Appendix A

Optics

A.1 Zemax Model 1

Bare Optical Layout

75 A.2. Zemax Model 2 76

A.2 Zemax Model 2

Pinhole Layout A.3. Zemax Model 3 77

A.3 Zemax Model 3

Focusing Lens Layout A.4. Zemax Model 4 78

A.4 Zemax Model 4

Final Optical Layout Zemax Configuration A.5. Zemax Model 5 79

A.5 Zemax Model 5

Proposed Layout for Larger Scanning Angle Appendix B

Mechanical Drawings and Assembly

B.1 Optical Test Fixture

80 2 x 0.098 0.354 M3x0.5 - 6H 0.236 0.500 0.250 0 0 6.693 5.512 4.528 2.165 1.181 0.837 0.344

2 x 0.098 THRU ALL 3 x 0.118 THRU M3x0.5 - 6H THRU ALL 2.000 1.606 1.065 0.828 0.591 0.394 0 0 6.693 5.512 5.315 4.528 2.953 2.165 1.181 0.492 0.197

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Stage Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 1 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 1:2 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 0.394 THRU 0.472 1.142

0.394

0 0 0.39 0.787 0 0.119 0.59 0.981

1.181

0.866

0.591 0.276

0.315 0.118 THRU 0.039 0 0

UNLESS OTHERWISE SPECIFIED: NAME DATE 0.098 0.394 DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14 CHECKED TITLE:

M3x0.5 - 6H 0.236 ENG APPR. MFG APPR. Laser Holder Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 2 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 0.984

0.768

0.217

0 2 x 0.081 THRU 0.276 0.194 0

0.981 0.492 0.512 0.906

0.588

R0.276 THRU 0.119 0

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Focus Lens Barrel Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 3 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 4 x 0.098 THRU ALL M3x0.5 - 6H THRU ALL 0.866 0.733 0.551 0.433 0.276 0.133 0.098 THRU ALL 0 0 M3x0.5 - 6H THRU ALL 0

0.133 0.315 0.591 0.733 0.866 0.098 THRU ALL 0.502 M3x0.5 - 6H THRU ALL 0.345 0.188

0 0

UNLESS OTHERWISE SPECIFIED: NAME DATE 0.433 DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. MM PLatform 1 Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 4 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 0.370 THRU

0.787

0.512

0.276 0.157 0 0 0 0.551 0.433 0.276 0.118 0.315 0.236 0.079

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Bearing Housing Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 5 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 A SECTION A-A

1.656 1.537 1.459 1.360 1.297 1.219 1.024

2 x 0.118

0.295 0.197

0 A 0 0 1.360 1.459 1.656 0.118 0.197 0.295 0.358 0.437 0.632 0.159 0.276

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. MM Platform 2 Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 6 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 PROHIBITED. IS WITHOUT THE WRITTEN PERMISSION OF REPRODUCTION IN PART OR AS A WHOLE . ANY DRAWING IS THE SOLE PROPERTY OF THE INFORMATION CONTAINED IN THIS PROPRIETARY AND CONFIDENTIAL 5 12.50 32.47 39.51 NEXT ASSY 7.05 20 0 0 5 APPLICATION 4 USED ON

0 0 MATERIAL FINISH 7.50 DIMENSIONS ARE IN INCHES UNLESS OTHERWISE SPECIFIED: DO NOT SCALE DRAWING 15 DELRIN 21.03 27.05 3 34.55 42.05 42.05 ENG APPR. DRAWN CHECKED Q.A. COMMENTS: MFG APPR. M3x0.5 - 6H 2 x 3 x M3x0.5 - 6H NAME DP 2.50 2.50 02/27/14 DATE 2 TITLE: SIZE SCALE: 1:1 A 7.50 9 6 MM Platform 3 6 DWG. NO. WEIGHT: 0 7

14.38

1 20 SHEET 1 OF REV 25

19.50

5.50 3 THRU 7 4.92 0 0 13 23

25.89 12.50

15.89 R7 THRU

3.97 0

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Magnifying Lens Barrel Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 8 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 2 x 2.50 9 M3x0.5 - 6H 6

50

35.47 2 x 3 THRU 25.83 6.50 4

6.35 0 0 0 50 8.75 11.46 22.95 28.75 41.25

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Magnifying Lens Holder Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 9 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 1:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 0.394 THRU

R0.295 0 0.118

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Lens Holder Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 10 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 5:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 B.1. Optical Test Fixture 91

This page was intentionally left blank B.2. Final Product Parts and Assembly 92

B.2 Final Product Parts and Assembly PROHIBITED. IS WITHOUT THE WRITTEN PERMISSION OF REPRODUCTION IN PART OR AS A WHOLE . ANY DRAWING IS THE SOLE PROPERTY OF THE INFORMATION CONTAINED IN THIS PROPRIETARY AND CONFIDENTIAL 5 NEXT ASSY APPLICATION 4 0.118 0.236 0.148 0.197 0.414 0.570 0.689 0.787 0.837 0.984 USED ON 0 0 MATERIAL FINISH DIMENSIONS ARE IN INCHES UNLESS OTHERWISE SPECIFIED: DO NOT SCALE DRAWING ALUMINUM 0 0 0.121 3 0.392 0.246 0.392 ENG APPR. DRAWN CHECKED Q.A. COMMENTS: MFG APPR.

1.283 NAME DP 1.874 2.046 02/27/14 DATE

2 2.244 TITLE: SIZE SCALE: 1:1 A DWG. NO. WEIGHT: Base 1 1 SHEET 1 OF 4.606 4.852 REV 5.000 5.000 PROHIBITED. IS WITHOUT THE WRITTEN PERMISSION OF REPRODUCTION IN PART OR AS A WHOLE . ANY DRAWING IS THE SOLE PROPERTY OF THE INFORMATION CONTAINED IN THIS PROPRIETARY AND CONFIDENTIAL 5 NEXT ASSY APPLICATION 4 2 x M3x0.5 - 6H USED ON 0 2 x

6-32 UNC 0.118 0.098 MATERIAL FINISH DIMENSIONS ARE IN INCHES UNLESS OTHERWISE SPECIFIED: 0.107 DO NOT SCALE DRAWING 0.787 DELRIN 0.236 0.295 3 0.276 0.370 ENG APPR. DRAWN CHECKED Q.A. COMMENTS: MFG APPR. 0

0.453 NAME DP

02/27/14 0.906 DATE 2 TITLE: 0 0.177 0.610 0.787 0 0.529 0.543 0.925 SIZE 0 0.295 0.610 0.669 0.787 SCALE: 2:1 A DWG. NO. Laser Holder WEIGHT: 2 1 SHEET 1 OF REV PROHIBITED. IS WITHOUT THE WRITTEN PERMISSION OF REPRODUCTION IN PART OR AS A WHOLE . ANY DRAWING IS THE SOLE PROPERTY OF THE INFORMATION CONTAINED IN THIS PROPRIETARY AND CONFIDENTIAL 5 NEXT ASSY APPLICATION

4 0

USED ON 6.35 MATERIAL FINISH DIMENSIONS ARE IN INCHES UNLESS OTHERWISE SPECIFIED: DO NOT SCALE DRAWING ALUMINUM 28.13 33.49 36.50 6.98 3 0 3 ENG APPR. DRAWN CHECKED Q.A. COMMENTS: MFG APPR.

0 3.84

NAME 5 DP 5.23 02/27/14

DATE 8.34 2 TITLE: SIZE SCALE: 2:1 A 20 Lens Support DWG. NO. WEIGHT: 30 3 1 SHEET 1 OF REV PROHIBITED. IS WITHOUT THE WRITTEN PERMISSION OF REPRODUCTION IN PART OR AS A WHOLE . ANY DRAWING IS THE SOLE PROPERTY OF THE INFORMATION CONTAINED IN THIS PROPRIETARY AND CONFIDENTIAL 5 0.059 0.079 0.197 0.315 0.512 0 0 NEXT ASSY APPLICATION

4 0 USED ON 0.295 0.354 0.482 MATERIAL FINISH DIMENSIONS ARE IN INCHES UNLESS OTHERWISE SPECIFIED:

DO NOT SCALE DRAWING 0.610

DELRIN 0.669

3 0.965 0.118 0.394 0.453 0.512 ENG APPR. DRAWN CHECKED Q.A. COMMENTS: MFG APPR. 0 NAME DP

02/27/14 0 DATE 2 0.098

TITLE: 0.197 SIZE SCALE: 2:1 A DWG. NO. Lens Holder WEIGHT: 4 1 SHEET 1 OF REV 4 x 1.60 THRU ALL 18.54 M2 - 6H THRU ALL 16.89 1.60 THRU ALL M2 - 6H THRU ALL

12.77 11.77

6.77 5.77

1.65 0 0 1 0 9.60 3.50 8.04 1.65 13.60 13.04 16.89 18.54

UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Platform 1 Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 5 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 0 70° 0.157 0.940 0.282 0.778

TRUE R0.125

1.000 0

0

2 x 0.102 0.325 0.049 0.120 5-40 UNC 0.250 0.352 0.394 0.424 0.787

0.541 0.531 0.256 0.246

0 0 0.419 0.602 0.786 UNLESS OTHERWISE SPECIFIED: NAME DATE

DIMENSIONS ARE IN INCHES DRAWN DP 02/27/14

CHECKED TITLE:

ENG APPR. MFG APPR. Platform 2 Q.A. PROPRIETARY AND CONFIDENTIAL COMMENTS: THE INFORMATION CONTAINED IN THIS MATERIAL SIZE DWG. NO. DRAWING IS THE SOLE PROPERTY OF DELRIN REV . ANY REPRODUCTION IN PART OR AS A WHOLE FINISH WITHOUT THE WRITTEN PERMISSION OF NEXT ASSY USED ON A 6 IS PROHIBITED. APPLICATION DO NOT SCALE DRAWING SCALE: 2:1 WEIGHT: SHEET 1 OF 1 5 4 3 2 1 B.2. Final Product Parts and Assembly 99

This page was intentionally left blank Appendix C

Electronics

C.1 Power Management Circuit

Figure C.1 Power Management Bill of Materials (BOM)

100 C.1. Power Management Circuit 101

Figure C.2 Power Management Schematic

. C.2. Microcontroller and Peripherals 102

C.2 Microcontroller and Peripherals

Figure C.3 Microcontroller BOM 1 C.2. Microcontroller and Peripherals 103

Figure C.4 Microcontroller BOM 2 C.2. Microcontroller and Peripherals 104

Figure C.5 Microcontroller Schematic C.3. High Voltage Amplifier 105

C.3 High Voltage Amplifier

Figure C.6 High Voltage Amplifier BOM C.3. High Voltage Amplifier 106

Figure C.7 High Voltage Amplifier Schematic C.4. Digital to Analog Converter Selection Chart 107

C.4 Digital to Analog Converter Selection Chart

Figure C.8 DAC Selection Chart Appendix D

Software

Figure D.1 Programming Code 1

108 109

Figure D.2 Programming Code 2 110

Figure D.3 Programming Code 3 111

Figure D.4 Programming Code 4 112

Figure D.5 Programming Code 5

Figure D.6 Programming Code 6