ECE 477 Digital Systems Senior Design Project Rev 8/09 Homework 6: Printed Circuit Board Layout Design Narrative

Team Code Name: _____Home Enhancement Suite______Group No. __10__ Team Member Completing This Homework: _____Nathan Irvin______E-mail Address of Team Member: ___nirvin______@ purdue.edu

Evaluation:

SCORE DESCRIPTION Excellent – among the best papers submitted for this assignment. Very few 10 corrections needed for version submitted in Final Report. Very good – all requirements aptly met. Minor additions/corrections needed for 9 version submitted in Final Report. Good – all requirements considered and addressed. Several noteworthy 8 additions/corrections needed for version submitted in Final Report. Average – all requirements basically met, but some revisions in content should 7 be made for the version submitted in the Final Report. Marginal – all requirements met at a nominal level. Significant revisions in 6 content should be made for the version submitted in the Final Report. Below the passing threshold – major revisions required to meet report * requirements at a nominal level. Revise and resubmit.

* Resubmissions are due within one week of the date of return, and will be awarded a score of “6” provided all report requirements have been met at a nominal level.

Comments: Grader: George Toh Score: 8/10 Good effort! Some minor changes before inclusion in the final report.

Comments regarding PCB layout:  Some components such as R2/3/20/21 have no reason to be on the bottom layer. All the components they connect to are on the top layer.  I noticed that the footprints for some of the larger capacitors were not 1206. Ensure you buy the right-sized components!  HDMI/PLIX – If you will be using it for high speed data transmission, ensure that your signal lines are as straight (with minimal vias) as possible.  If space is too much of a factor around the microcontroller, consider downsizing to 0805 or 0603 caps instead. ECE 477 Digital Systems Senior Design Project Rev 8/09

Introduction The Home Enhancement Suite is a package that will allow a user to easily configure settings that will autonomously be controlled by the Suite when the user’s unique RFID tag is scanned. In addition to the main module box, there will be RFID readers both internally and externally of one door, presumably the exterior door, that will allow the Suite to unlock the door when an appropriate ID is scanned. Settings that the Suite will control include the lighting and control over an HDMI device, such as a television. There will be a total of three PCBs incorporated in the project. The main module PCB will be the control unit and contain the micro-controller. The RFID modules will then each have their own PCB. The RFID module PCBs will be identical to each other and function similarly as well with the exception that one will be configured in software as the exterior unit and when scanned the settings will “turn on”, while the other will be the interior unit and when scanned “turn off” the settings in the room. The size of the units can largely be based on the overall footprint of the necessary PCB and therefore the components will not necessarily need to be in close proximity to each other, aside from doing so to prevent unwanted noise coupled by long traces. This allows the freedom to comfortably place components with no major PCB layout issues. The following report will outline the more specific layout requirements pertaining to various aspects of the Suite.

1.0 PCB Layout Design Considerations - Overall The main box of the Suite will be housing an ID-12, RFID reader such that if the user is already in the house or enters from a room other than the locking door, they will be able to “sign-in” to the room and have their settings applied. Keeping that in mind, it is necessary that the ID-12 be placed as close to the exterior of the box as possible. For that reason, the PCB will be mounted to the top of the box with the ID-12 on the side closest to the box allowing for the maximum possible signal strength. The taller components including the transformer, aluminum electrolytic capacitors, Xbee radio chip and all external port connectors will be mounted on the opposite side of the PCB. The ID-12 itself is 6mm tall and therefore any small surface mount parts will easily still fit on the back side of the PCB if necessary.

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There are no major signal routing concerns, so all steps will be taken to minimize the length as much as possible, especially those going to and from the ethernet external PHY IC. The concerns of EMI are greatly reduced by the use of a ground plane. No components are expected to create excessive amounts of EMI and therefore the ground plane should be sufficient to ensure no issues form. At this time, no filter circuits have been implemented into the design. The trace widths will typically be 8 mil throughout both board designs, the main and the RFID module. They will be widened to 24 mil for the electric strike circuit. The traces in this circuit will run 400 mA when in use. The power supply circuit will also have wider traces to compensate for the full load of the system. When the electric strike is active, portions of the circuit could run approximately .8-1A depending on which other functions of the Suite are occurring. These traces will be approximately 100 mil to be safe which is well above the recommend of 60 mil.[1] The PLIX, Power Line Interface for X-10 Communication, requires an external oscillator and it is important that this be placed as close to the IC as possible with load capacitors in place. [2] The external PHY for the ethernet communication also requires an oscillator and therefore the same consideration has been given to it in regards to proximity to the IC.[3] The ethernet signal requires “magnetics” so to optimize board space a jack called the MagJack with internal “magnetics” was selected.[4] The RFID reader PCBs do not have any major requirements as they are simple and are only used to obtain an RFID and send the signal using an Xbee module to the main box. The requirement is simply that it be a reasonable size (not too large). The size was ultimately determined by the batter pack, Xbee radio and ID-12 reader which allowed ample board space for the remaining components, including the DC/DC boost converter.

2.0 PCB Layout Design Considerations - Microcontroller The micro-controller has very specific guidelines that were followed.[5] A bulk cap (tantalum) of 4.7uF is placed close to the IC. All power lines will route passed the bulk cap and

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then to the various pins of the micro. For this reason, the trace to the bulk cap has been chosen to be 12 mil. For the Suite, the micro-controller is not required to source ample amounts of power. All decoupling capacitors are placed on the same side of the board as the micro and within one-quarter inch of the IC itself. To maintain a standard throughout the board, the capacitors were chosen to be size 1206 presenting a bit of a challenge, but manageable. All power and ground pins of the micro are connected first to a decoupling capacitor. The micro itself is placed close to the center of the board with an emphasis on being close to all external port connectors as recommended in the Motorola Semiconductor Application Note[6]. External connections include interfacing with the HDMI port. The remaining off board connections are the PLIX which first communicates with the PLIX IC and the ethernet, which again is communicated through the external PHY. These components were placed near their connectors as well to minimize EMI problems.

3.0 PCB Layout Design Considerations - Power Supply Fortunately, the majority of the circuitry in the Home Suite is digital in contrast to analog. The only circuits that will need to be kept separate are the ambient light circuit, the electric strike circuit, simply because of the high current and the ability to couple into the digital signal lines, and some dedicated analog power to the ethernet PHY[3]. A ground plane is going to be utilized for too reasons. The first is to minimize inductance of the ground return and the second is to act as a heat sink for the linear regulator. If the heat sink is not able to extend over the entirety of the board, as it will on the RFID PCB, a star grounding system will be used from the plane. The power rails will also operate in a star pattern as much as possible. A dedicated trace will be needed for the ethernet PHY. There is a need for both 5V and 3.3V and therefore these circuits will also be kept separate as much as possible. A transient voltage suppressor diode is being used immediately following the secondary terminals for protection. This is followed by a filter cap. High frequency noise suppression caps are used after the linear regulator and the DC/DC converter and kept as close as possible to the components.

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4.0 Summary Overall with the ability to expand the PCB as needed, the layout has not been a primary concern. Based on various information provided in the data sheets and application notes, a relatively simple PCB results. The major concerns are the trace widths for the power supply and the electric strike circuit as well as minimize trace length for all the signals that ultimately leave the board. The analog and digital signals will be kept separate as much as possible as will the 3.3 and 5V circuits. There are no major concerns with EMI as a ground plane will be used to minimize the inductance of the ground return.

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List of References

[1] D.Meyer, “PCB Fabrication Process and Layout Basics,”Lecture Notes for ECE477, Digital Senior Design, https://engineering.purdue.edu/ece477/Notes/PDF/4-Mod5_CP_2011.pdf, Purdue University, Spring Semester, 2012.

[2] Micromint Serial PLIX [Online]. Available: http://www.micromint.com/datasheets/serplix.pdf [Accessed: Feb. 18, 2012]

[3] DP83848C PHYTER Commercial Temperature Single Port 10/100 Mb/s Ethernet Physical Layer Transceiver [Online]. Available: http://www.ti.com/lit/ds/symlink/dp83848c.pdf [Accessed: Feb. 21, 2012]

[4] 10/100BT, Tab Down, Shielded [Online]. Available: http://www.belfuse.com/Data/Datasheets/SI-60062-F.pdf [Accessed: Feb 22, 2012]

[5] PIC32MX664F064L [Online]. Available: http://ww1.microchip.com/downloads/en/DeviceDoc/61156G.pdf [Accessed: Feb 18, 2012]

[6] M. Glenewinkel, “System Design and Layout Techniques for Noise Reduction in MCU- Based Systems” [Online]. Available: https://engineering.purdue.edu/ece477/Homework/CommonRefs/AN1259.pdf [Accessed: Feb 18, 2012]

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