doi:10.3723/ut.30.195 International Journal of the Society for Underwater Technology, Vol 30, No 4, pp 195–199, 2012

Development of a head-up displayed diving computer capability for full face masks

1, 2 3 4 1 Arne Sieber* , Benjamin Kuch , Peter Enoksson and Milena Stoyanova-Sieber Pa per Technical 1Seabear Diving Technology, Puchstrasse 17, 8020 Graz, Austria 2ACREO AB, Arvid Hedvalls Backe 4, 41133 Gothenburg, Sweden 3Scuola Superiore Sant’Anna - RETIS Lab, via Moruzzi 1, 56124 Pisa, Italy 4MC2, Chalmers University of Technology, Gothenburg, Sweden

Abstract diving computer even at distances of 20cm to 40cm Professional divers often dive in conditions of very low visi- becomes impossible. An HUD has the potential to bility. In such situations, a head-up display has many advan- be an essential tool for many sectors of the com- tages as water clarity does not affect the ability to see the mercial diving industry and may increase diving display. In addition, a head-up display allows divers to con- safety. tinuously monitor all relevant dive data without interrupting Full face masks are predominantly used by profes- their work. The present paper details the development of a sional divers. They offer a number of advantages over new ­diving computer that has been designed with a head- standard half-masks: thermal protection of the face; up display and integrated into an AGA type full face mask. protection in polluted waters; and the capability to The device includes a full colour display, depth sensor, tilt- use voice communications. Full face masks are also compensated compass and a tank sensor. Typical sometimes used by divers because, in dive relevant data (depth, time, obligations) the event of an toxicity accident, a full face including tank pressure and heading are displayed and stored in the internal flash memory. mask remains fixed on ’s face and would continue to provide gas. Keywords: diving computer, full face mask, head-up dis- Irrespective of the reasons for wearing a full play, AGA mask, head-up diving computer, tilt-compensated face mask, it provides an obvious platform in which compass to incorporate an HUD. The present study reports on the development of an HUD for a full face mask with the specific design criteria of incorpo- 1. Introduction rating a tank-integrated, -capable dive com- Diving computers are usually integrated in a con- puter. In addition, the design criteria requires the sole, or are wrist-worn and display dive relevant display to have excellent readability independent data such as depth, time and decompression obli- of water visibility, with a virtual reading distance of gations (Azzopardi and Sayer, 2010). The continu- 1m, as well as adjustable optics, a tilt-compensated ous monitoring of such data can be extremely compass for hands-free underwater navigation important for safety when diving. However, a wrist- and an interface for additional accessories, such worn or console requires manual as the oxygen (pO2) sensors of a action in order to read the display: the user has rebreather. to grab the console or twist the wrist-worn unit to view it. 2. Methods In contrast, a head-up display (HUD) directly mounted on a or on a mouthpiece 2.1. State-of-the-art head-up displays offers a hands-free to monitoring a diver’s Mounting a traditional dive computer directly in status. The freedom of not having to refer to a wrist- front of the visor of a full face mask is theoretically worn or console-mounted display is especially possible. However, a person with normal sight ability ­beneficial in cases where a diver is performing cannot focus on objects in such close vicinity, and hands-on , as the workflow is not so an additional optical system would have to be interrupted. An HUD can also be valuable in bad introduced in order to achieve readability. In the ­visibility and ‘’ conditions, where the visibil- simplest form, such a system could consist of a sin- ity is impaired to such an extent that reading of a gle convex in the optical pathway between the dive computer display and the eye. HUDs are typi- * Contact author. E-mail address: [email protected] cally designed to produce an image of a display that

195 Sieber et al. Development of a head-up displayed diving computer capability for full face masks

can be read at a more comfortable ‘virtual’ distance LED and showed an identical copy of the screen of 0.5–1.0m (Koss and Sieber, 2011a). of the primary handset. The device featured a unique optical design: the optical path of the system 2.1.1. DataMask® and CompuMask® head-up consisted of a solid polymethyl methacrylate block displays (PMMA; a transparent thermoplastic), which was The Aeris CompuMask® HUD and the Oceanic Data- glued directly onto the visor of a diving mask. Using Mask® HUD are computers that a prism-shaped lens mounted inside the mask pro- are fully integrated into a traditional diving mask, duced a 400 × 200mm² image of the display at a based on a liquid crystal display (LCD), and have an comfortable virtual reading distance of 1m. optical system. However, they are both closed designs Along with the standard version of the display for and, therefore, permit no additional accessories traditional diving half-masks, a special design for full to be added. The masks are well designed but, at face masks was also developed. Both systems were present, are only available in one size. extensively tested in various conditions. Although the designs worked well, divers found the cable from 2.1.2. Head-mounted displays for the primary handset to the HUD to be annoying. In missions addition, only very slight improper positioning of Gallagher (1999) and Belcher et al. (2003) devel- the glued-on display produced misaligned and dis- oped HUDs for countermine diving missions. The torted images. designs are larger, are more expensive to produce Problems with misalignment can be avoided by and have high-power consumption. Designed as mil- introducing a multi-lens system, with at least one itary equipment, they are not available to the public. concave and one convex lens included in order to facilitate adjusting the magnification of the virtual 2.1.3. Head-mounted displays for image. In theory, the optical parts required for an State-of-the-art rebreathers are equipped with LED- adjustable HUD can be small (with the diameter of based HUDs. These are simple devices mounted being ~10–15mm) with a similarly compact within the diver’s field of vision on a support on the pressure-proof housing. Therefore, high pressure rebreather mouthpiece. Typically they consist of one resistance can be achieved with inexpensive designs or more LED displays, but the information content fabricated from plastics. is obviously limited, as they usually can only display A prototype of an independent HUD specially the pO2 of the loop. More advanced approaches also designed for full face masks differed from previous use coding of the LEDs, usually blinking sequences, approaches by having the HUD connected via a cable to increase the information content. However, read- to a primary handset (DC). The independent elec- ing and interpretation of the sequences require tronics included with it comprised a microcontroller, both training and . a 96 × 64 colour organic LED display, a digital pres- sure and sensor and an analog input for 2.1.4. Graphical head-up diving computer readout of a tank pressure sensor. The device was Koss and Sieber (2011a) mounted a graphical dis- designed to be mounted outside a full face mask. play with an optical system directly onto the mouth- Although the prototype worked well, the main prob- piece of a rebreather. With a carefully positioned lem again was the ability to adjust the device. device, good readability of standard dive data was achieved. However, mouthpiece movements resulted 2.2. New design for full face mask head-up in optical misalignments where the display partly displays moved out of sight. In the same study, they achieved The design for an HUD especially for full better results when the device was fitted to a full face masks was based on the AGA mask (Interspiro, face mask when it was mechanically fixed in a position previously part of the AGA Corporation). The AGA relative to the eyes and outside of the diving mask. design is dominant in the full face mask market However, there was still water between the ocular of and has been adopted by several other manufac- the device and the visor of the full face mask, and tures (e.g. Ocean Technology Systems (OTS) and so the readability of the display could be impaired Poseidon Diving Systems). These AGA-type masks with bad water visibility. featured a large visor with opaque side windows, which permitted straightforward 2.1.5. computer with secondary ­retrofitting of a port. head-up display Koss and Sieber (2011a,b) developed a technical 2.2.1. Basic HUD design diving computer with capability incorporated The mechanical design of the HUD was round- into an HUD. The HUD was based on a white organic shaped, with the shaft of the display fitted into the

196 Vol 30, No 4, 2012

port on the mask and sealed with a standard nitrile which is a two-axis magnetometer) that measure butadiene rubber (NBR) O-ring located in a groove the two-dimensional magnetic vectors used for on the port (Figs 1 and 2). The prototype was made heading calculations. There is the requirement for from polyvinyl chloride (PVC), and the cylindrical the magnetometers to be mounted in the horizon- shape of the device meant it would be simple and tal plane, however, this is problematic in compasses cost-effective to be manufactured. used for diving because of the lack of horizontal The optical path consisted of three parts: a con- reference when the diver is moving in three dimen- vex lens with a focal length of 40mm and diameter sions. Any slight tilt with an electronic compass that of 10mm that formed the eyepiece of the device, uses a single two-axis magnetometer will give incor- and a stainless steel mirror directly behind the lens rect readings. that redirected the optical path towards the final In cases of small tilt angles (also referred to as part, the 96 × 64 pixel organic LED display. A con- pitch and roll) a compensation can be achieved cave lens (f = -15mm, diameter = 13mm) was with a two-axis accelerometer. Since the accelerom- added to the optical path at a distance of 12mm in eter output is subject to gravity, pitch and roll can front of the display in order to achieve an optical be calculated directly from the acceleration vector. magnification equal to 1. The HUD could be The angles are then used to calculate a tilt-compen- rotated, as well as moved in an axial direction, to sated heading. However, the present design permit- permit easy and uncomplicated adjustment of the ted the diver to rotate the whole unit, which would device to the diver’s eye. produce large pitch angles. Therefore, a three-axial The aluminium tank pressure sensor was con- magnetometer and a three-axial compass were inte- nected to the HUD diving computer via a six-core grated, generating a true three-dimensional mag- 6mm polyurethane cable. The battery compartment netic and acceleration vector which could be used for a standard lithium ion (Li-ion) CR2 cell was for the tilt-compensated heading calculation inside the tank pressure housing. (STMicrosystems, 2010; Kionix, 2007; Salhuana, 2007). 2.2.2. Electronic compass Electronic compasses are subject to interferences/ An electronic compass was designed from two distortions, and so for the present HUD design, a orthogonally-mounted magnetometers (one of calibration of the device was required. Hard iron distortions only produce an offset of the magnetic vectors, thus a calibration routine was implemented collecting magnetometer readings while the device was randomly rotated in three dimensions by the user. Maxima and minima readings were collected for each vector and used to calculate offset and gain for each magnetometer axis (Honeywell, 2009). Compass plots of an ideal compass without inter- ference are of circular shape. However, soft iron distortions cause an elliptic deformation of the shape and cannot be compensated for by a simple calibration routine. Therefore, the HUD design Fig 1: Head-up dive computer, port and visor of an AGA-type avoided having any soft iron in close vicinity to the full face mask magnetometer. For instance, surface mount device capacitors or resistors were attached at a safe dis- tance because their contacts contain nickel.

2.2.3. Electronic design Fig 3 shows the outline of the electronics used in the present HUD design. The core component was an Atmega644PV (Atmel) 8-bit reduced instruc- tion set computer (RISC) microprocessor, which was retained from previous developments. A 0.96in , green, (RGB) display with 96 × 64 pixels (Densitron) was interfaced via a serial peripheral interface (SPI) bus. The digital pressure sensor MS5541 from Intersema Sensoric SA measured pres- Fig 2: View of the HUD assembly from a diver’s perspective sures up to 14bar with 15-bit resolution and could

197 Sieber et al. Development of a head-up displayed diving computer capability for full face masks

(XML) files. Besides the (depth graph, ceiling graph) and dive-specific data (dive time, maximum depth), the final tissue saturation at the end of the dive was also shown in a bar plot. Addi- tional dive parameters such as dive conditions and information about the equipment could also be added by the user. The dive profiles were capable of being converted into the (DAN) DL7 Level 1 Standard (Denoble, 2006). The third part of the software suite was used to upgrade the firmware of the dive computer. The program memory space of the dive computer was divided in a bootloader and an application section. Fig 3: Electronic components of the head-up diving During the firmware upgrade, the bootloader computer received a new firmware package from the PC and programmed the flash memory. Copy protection also be used for water temperature measurement. and manipulation safety was achieved by advanced Dive-relevant data were stored on an internal flash encryption standard (AES) of the firmware package memory chip with 4Mbit (DataFlash). (Atmel Corporation, 2010). An automatic software All components were carefully selected to achieve update of the PC application itself was also imple- extremely low power consumption in combination mented: after each program start, an XML remote with a low minimum supply voltage of 2.5V. A stand- procedure call (XML-RPC) (Apache Corporation, ard Li-ion battery-type was chosen for the power 2010) was sent to a corresponding web server to supply. As described earlier, a three-axis magnetom- check if a new software version was available, and eter and a three-axis accelerometer were integrated any updated version was downloaded and installed in the design to provide the capability to produce automatically. The PC software was developed under tilt-compensated headings. Eclipse SDK 3.4.1 in Java 1.6 and the Standard Widget Toolkit. This made the application platform 2.2.4. Software design independent and permitted data to be compiled on The firmware for the microprocessor was developed Windows, Unix, Linux and Mac systems. Data trans- under Eclipse and a GNU C compiler (WinAVR). fer between HUC and PC was established via serial The basic software features calculated the main phys- communication at 115 200 baud. ical parameters of a dive (depth, time, maximum depth) and estimated the main physiological obliga- tions related to the dive profile (remaining no 3. Results decompression time, decompression requirements Fig 5 shows an HUD prototype mounted in an OTS modified from the Buehlmann ZHL-16 dataset with full face mask. The housing was fabricated from gradient factors and micro-bubble extension). It black PVC, and the port and tank pressure housing then calculated the headings and converted the read were turned from seawater-resistant aluminium. out from the tank pressure sensor. The unit facili- tated data storage equivalent to 120 diving hours. For simple management and configuration of the head-up dive computer, a PC application was developed. The first part of the application was dedicated to permitting the diver to configure and customise the HUD diving computer, where all adjustments like Nitrox mix, time settings and decompression conservatism level could be set. It also provided the capability to personalise the dive computer with features such as a start-up pic- ture, the owner’s name and an emergency phone number. The second part of the application was a typical diving computer logbook function used for dive data download and visualisation (Fig 4). Dive data Fig 4: An example of the dive data display generated by the were converted into extensible mark-up language PC software following a pressure-chamber dive

198 Vol 30, No 4, 2012

this task was not difficult to achieve for a trained person, it presents some problems from a legal point of view, as any non-certified modification probably invalidates the mask CE accreditation. Divers were satisfied with the new device, mainly because it provides a true hands-free solution for monitoring data relevant to dive management. This is especially welcomed in situations where a diver is working underwater or where there is low visibility.

References Apache Corporation. (2010). Apache XML-RPC Java imple- Fig 5: Open water tests of the HUD mentation. Houston: Apache. Available at http://ws. apache.org/xmlrpc/, last accessed <03 January 2012>. The optical path was filled with dry air in order to Atmel Corporation. (2006). Application Note AVR231: AES avoid condensation from humidity on the lenses; Bootloader. Available at http://atmel.com/dyn/resources/ the electronic compartment was filled with silicone prod_documents/doc2589.pdf, last accessed <03 January 2012>. gel. The port was bonded to the mask side window Azzopardi E and Sayer MDJ. (2010). A review of the techni- using standard methacrylate glue. A finite element cal specifications of 47 models of diving decompression pressure simulation was performed in SolidWorks computer. Underwater Technology 29: 63–72. 2008 and indicated that the housing should with- Belcher EO, Gallagher DG, Barone JR and Honaker RE. stand greater than 10bar absolute. (2003). Acoustic lens camera and underwater display For software verification and validation, labora- combine to provide efficient and effective hull and berth inspections. In: Proc. MTS/IEEE Oceans 2003, 1361–1367. tory test software was developed under National Denoble PJ. (2006). Project dive exploration – DL7 Stand- Instruments LabVIEW 8.0. It allowed simulation of ard. Divers Alert Network. dives either in accelerated or real time, while tissue Gallagher DG. (1999). Development of miniature, head- saturations calculated by the dive computer were mounted, virtual image displays for navy divers. MTS/ monitored and stored on graphs produced by IEEE OCEANS’ 99, Riding the Crest into the 21st Century, vol 3, 1098–1104. the software. The compass was laboratory tested: Honeywell. (2009). Electronic compass design guide using The an accuracy of ±2.7° was achieved in the horizontal HMC5843 digital compass IC. Morristown, NJ: Honeywell. position, and at pitch/roll angles of ±45°, the accu- Kionix. (2007). Handheld electronic compass applications racy was reduced to ±4.2° (Kuch et al., 2011). using a Kionix MEMS tri-axis accelerometer, AN 006. Prior to real dives, the device was successfully ­Ithaca, NY: Kionix. tested in a small hyperbaric test chamber for pres- Koss B and Sieber A. (2011a). Development of a graphical head-up display (HUD) for . Underwater sure and water resistance up to 100msw. The device Technology 29: 203–208. was used by three divers in a total 15 dives to a max- Koss B and Sieber A. (2011b). Head-mounted display for imum depth of 45msw. All divers reported excel- diving computer platform. Journal of Display Technology 7: lent readability. 193–199. Kuch B, Haasl S, Wagner M, Buttazzo G and Sieber A. (2011). Preliminary report: Embedded platform for inertial 4. Discussion based underwater navigation. 9th International Workshop on Intelligent in Embedded Systems, Regensburg, A novel HUD for AGA-type full face masks was Germany. developed. The device was tested in the Mediterra- Salhuana L. (2007). Tilt sensing using linear accelerometers. nean and in Austrian lakes and was considered Freescale semiconductor. Austin: Freescale Semicon- to have worked well. The device could be adjusted ductor. STMicrosystems. (2010). Application note AN3192. Geneva: easily by simply rotating the display and/or moving STMicrosystems. Available at www.pololu.com/file/ it in axial direction. The full face mask required a download/LSM303DLH-compass-app-note.pdf?file_ hole to be drilled/milled for the port. Even though id=0J434, last accessed <03 January 2012>.

199