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EE 477 Final Report

1. Figure 1 1 The Gauntlet ECE 477 Final Report Spring 2010 Internally the Gauntlet can be divided into four main subsections central control environmental sensors user interface and power The block diagram in Figure 1 2 shows these subsections and how they interface to one another The central control consisting of a PIC24F microcontroller and Flash storage coordinates each subsection and provides overall control for the Gauntlet The user interface includes pushbuttons an LCD and the audio output circuitry Environmental sensors consist of a GPS unit to provide location and velocity information a combination pressure sensor thermometer providing altitude and temperature and an accelerometer to provide airtime measurements Power includes a rechargeable lithium polymer battery its charger and monitor a buck boost converter to provide power to the rest of the circuit and a shutdown control to protect against battery undervoltage Environmental Sensors Programmer Header microSD Card User Interface Polstar PMB 648 GPS Pushbuttons SCP1000 D01 Altimeter Thermometer PIC24FJ256GA106 Microcontroller NHD C0220BiZ 20x2 LCD VS1011E ADXL345 Accelerometer Headphone MP3 Decoder Jack LTC4150IMS Battery Monitor Lithium Polyme
2. 4 0 Ground Mobile TQ Quality Factors 10 0 Commercial product TL Learning Factor 1 0 In production for gt 2 years since 2001 Entire design Ap 5 936 MTTF 19 years MCP73811 Charger A C1 nr Co mg To AL Parameter name Description Value Comments Ci Die Complexity 0 01 Linear less than 100 transistors TT Temperature Factor 21 Tymax 105 C Linear C2 Package Failure Rate 0 0019 Hermetic SMT 5 pins used 6 pins TE Environment Factor 4 0 Ground Mobile TQ Quality Factors 10 0 Commercial product TL Learning Factor 1 0 In production for gt 2 years since 2007 Entire design Ap 2 176 MTTF 53 years The failure calculations above are an initial cause for some concern because they are all above the recommended value of one failure per 1 million hours However upon further analysis some of these concerns are mitigated Using 10 as a quality factor for commercial components is probably excessive given the standards of manufacturing today The use of a lower quality factor such as 5 would dramatically reduce the estimated failure rates and create a more accurate model Other conservative estimations for individual components could also make the model more accurate and decrease the estimated failure rate The worst case of 32 bits was used for die complexity for the VS1011E with a junction temperature of 50 C The die complexity is probably slightly low
3. Abstract The Gauntlet is an arm wearable device which provides snowsports enthusiasts with real time information current velocity temperature altitude and airtime via headphone audio In addition it has an emergency mode which uses GPS to navigate the user back to a programmable safe location The device is powered by a lithium polymer battery which is monitored and recharged in circuit The Gauntlet has a target battery life of ten hours so its components have been selected to be low power and the device will be operational in subfreezing temperatures This report includes descriptions of the design and creation of the Gauntlet as well as several analyses of the product in the context of the environment the patent system ethics reliability and safety 1 0 Project Overview and Block Diagram The Gauntlet has two primary operating modes a normal mode which communicates a user s velocity temperature altitude and airtime over the user s headphones and an emergency mode which navigates the user back to an initial safe point if the user becomes lost The user interacts with the Gauntlet using a character LCD and three pushbuttons shown in Figure 1 1 which display and control a menu based user interface The user can change preferences such as headphone volume and audio output timing Important information such as preferences battery information and the GPS waypoint path are saved to persistent microSD storage
4. A PIC24F simulator was used for initial testing and debugging of newly written code The PIC can also be operated using an in circuit debugger and debugging information during normal use is communicated on the character LCD 28 ECE 477 Final Report Spring 2010 10 6 Software Design Narrative 10 6 1 Input The microcontroller takes input from five primary sources the accelerometer the altimeter the battery the GPS and the pushbuttons The accelerometer altimeter pushbuttons and battery voltage are polled at regular intervals The GPS and the charge counter both send data asynchronously to the PIC in the form of NMEA messages or pin interrupts This implies some differences in the way the underlying hardware drivers work For the SPI based input devices the sensor SPI bus clocked at 500 kHz is utilized Once a second the altimeter is triggered to begin an acquisition conversion sequence by the PIC When the altimeter responds with a data ready interrupt the PIC s interrupt handler signals the main loop to 1 pull the altimeter s chip select low and 2 read the altitude by writing a read command and receiving a 15 bit value back Using the table described in 31 this value is converted to an altitude in meters The accelerometer in contrast will be set to perform its own sample buffering no trigger is necessary Approximately ten times a second the accelerometer s chip select will be pulled low and the values of the X Y
5. waypoints are set by the destination waypoint setting means and guidance starts displaying means for displaying the positional information stored in the history storing means and destination waypoint selection means for selecting a destination waypoint with referring to the displayed positional information further characterized in that the predetermined timing refers to a timing when a predetermined time has passed since guidance started for the set destination waypoint and the history storing means determines whether the predetermined time has passed and stores positional information on the set destination waypoints therein 4 1 3 Flaik Sports Armband Commercial Product 13 ECE 477 Final Report Spring 2010 The Flaik sports armband is a handheld navigation device designed for sports enthusiasts It features a GPS device and allows snowsports enthusiasts to track their movements over the course of their skiing and snowboarding trips It also features radio communication capability to track other users such as a ski instructor tracking his or her ski school students for the day 4 2 Analysis of Patent Liability 4 2 1 Route Based on Distance Patent No 7 627 423 The Gauntlet has a number of similarities to features of the device mentioned in this patent in particular the use of elevation data in conjunction with the GPS and the idea of a personal navigation device that tracks one s movements This patent seems to be focused on a perso
6. which I wrote up as a tutorial to share with the rest of the class Using this knowledge I designed footprints for all of the parts needed for the Gauntlet Jacob discovered additional features of the PADS layout software and I implemented these to perfect the footprints for the PADS PCB Jacob Kelli and Sean were very helpful in arranging ECE 477 Final Report Spring 2010 most of the PCB components into unions at which point I ran the autorouter and proceeded to tweak the output from the autorouter to complete the PCB design for the Gauntlet When the PCB arrived I was in charge of all of the soldering for the Gauntlet particularly parts that were more difficult to solder by hand These included the microcontroller mp3 decoder IC analog comparator IC charge counter IC and buck boost converter IC as these came in QFP and SSOP packages When problems arose related to the microcontroller and audio decoder ICs I was in charge of performing the fly wiring on the chips which was extremely difficult in most cases Once the PCB was fully constructed I was responsible for machining the case to ensure parts fit within the Gauntlet casing This included carefully drilling holes for the audio jack and DC power jack in the back of the case drilling mounting holes for the screws to fasten the power switch to the back of the case adding eyelets to the bottom of the case to allow straps to be connected to the case and machining holes and cut outs on
7. 1 Default aspx Accessed Jan 29 2010 9 PIC24FJ256GA110 Family Data Sheet Microchip Technology Inc Dec 10 2009 Online Available http ww1 microchip com downloads en DeviceDoc 39905d pdf Accessed Feb 3 2010 10 XMEGA Al Microcontroller Atmel Jan 2010 Online Available http www atmel com dyn resources prod_documents doc8067 pdf Accessed Feb 3 2010 11 A S Brooks Route based on distance U S Patent 7 627 423 Dec 1 2009 12 K Tomizawa Navigation device method and program U S Patent 7 565 240 July 21 2009 34 ECE 477 Final Report Spring 2010 13 Flaik Armband for Ski Adventurers Tuvie Online Available http www tuvie com flaik armband for ski adventurers Accessed Mar 30 2010 14 United States Department of Defense MIL HDBK 217F Military Handbook on Reliability Prediction of Electronic Equipment Dec 1991 Online Available https engineering purdue edu ece477 Homework CommonRefs Mil Hdbk 217F pdf Accessed April 8 2010 15 ed LTC3440 Micropower Synchronous Buck Boost DC DC Converter Linear Technology 2001 Online Available http cds linear com docs Datasheet 3440fb pdf Accessed Feb 18 2010 16 ey Microchip MCP73811 2 Simple Miniature Single Cell Fully Integrated Li Ion Li Polymer Charge Management Controllers Microchip June 25 2007 Online Available h
8. 12 99 1 12 99 Linear Linear LTC3440EMS 600mA Buck Boost 3 3V Regulator 3 24 1 3 24 Linear Linear LTC4150IMS Battery Monitor Fuel Gauge 245 1 2 45 Microchip Microchip MCP73811T LiPo Battery Charge Management IC 0 63 1 0 63 Digi Key Newhaven Display NHD C0220BiZ FSW 3 3V 20x2 Character LCD 10 52 1 10 52 FBW 3V3M Digi Key Analog ADCMP361 Analog Comparator 1 53 1 1 53 Digi Key C amp K Components L20101 1SS03Q On Off Slide Switch 2 22 1 2 22 Digi Key Stackpole Electronics CSR 1 2 0 1 1 I OTO Sense Resistor 0 84 1 0 84 Digi Key Abracon Corporation ABLS 12 000MHZ B4 T 12 MHz Oscillator 0 41 2 0 82 Digi Key Panasonic EVQ 11A09K Pushbutton 0 14 3 0 42 OKW OKW Ergo Case M Package Eyelets Straps 30 28 1 30 28 Various Various Generic Passive Components 20 00 Resistors Capacitors TOTAL 228 57 ECE 477 Final Report Spring 2010 Appendix F FMECA Worksheet Power Subsystem Failure Failure Mode Possible Causes Failure Effects Method of Criticality Remarks No Detection Al Power rail 0V Short disconnect in Nothing turns on Observation Low power supply circuit or operates A2 Power rail gt 3 3 Buck boost failure Damage to Observation Medium Specific damage to V short to battery components circuitry is throughout unpredictable likely circuit loss of not repairable functionality A3 Battery Analog comparator Possible battery Observation High undervoltage fails excessive no
9. 32 ECE 477 Final Report Spring 2010 12 0 Summary and Conclusions Team 3 accomplished the design construction and testing of a fully functional GPS unit for skiers and snowboarders During this process we brainstormed and selected success criteria analyzed design constraints for the device researched possible constituent components and designed the packaging for the device We subsequently designed a schematic and used it to lay out a custom printed circuit board Upon receiving and populating this PCB we crafted low level drivers higher level algorithms and control software and a user interface for the Gauntlet to satisfy all of the success criteria Parallel to the completion of the product we analyzed the device s safety and reliability as well as ethical and environmental concerns and we researched possible patent liabilities we might encounter during the manufacture of the Gauntlet During this process the team learned multiple useful computer and electrical engineering concepts how to design a circuit for maximum reliability and safety how to correctly design a digital system how to test and debug embedded systems during manufacture and how to best ensure that the manufacture of a product is legal and ethical Overall we have each learned how to take a digital embedded system from an initial concept to a working reality 33 ECE 477 Final Report Spring 2010 13 0 References 1 V Blake Flaik skis its way to a de
10. MP xCS MP 23 RP137 RC14 48 MP xDCS BSYNC MP 13 Rp24 RD1 49 MP xRESET MP 3 RP22 RD3 51 CC SHDN CC 5 RP25 RD4 52 CC INT CC 10 RP20 RD5 53 CC POL CC 6 RFO 58 PB 1 Pushbutton RF1 59 PB 2 Pushbutton REO 60 PB 3 Pushbutton RE3 63 Alt Trig Alt 8 RE4 64 Alt PD Alt 9 G 2 ECE 477 Final Report Appendix H PIC24F Memory Map PROGRAM SPACE MEMORY MAP PIC24FJ256GA1XX GOTO Instruction Reset Address Interrupt Vector Table Altemate Vector Table User Flash Program Memory 8 87K instructions u 5 E v 5 a Flash Config Words Unimplemented Read 0 5 D 2 Device Config Registers 3 Cc S g eS c ke DEVID 2 02ABFEh 02ACOOh 7FFFFFh g00000h F7FFFEh F80000h F8000Eh F80010h FEFFFEh FF0000h FFFFFFh MSB Address 0001h O7FFh 0801h 1FFFh 2001h 47FFh 4801h 7FFFh 8001h FFFFh Spring 2010 DATA SPACE MEMORY MAP PIC24FJ256GA110 LSB MSB LSB Address SFR Space 0000h 07FEh 0800h 1FFEh 2000h Data RAM 1 47FEh 4800h Unimplemented Read as 0 7FFFh 8000h 1 Program Space Visibility Area 1 FFFEh 2009 Microchip Technology Inc H 1 ECE 477 Final Report Spring 2010 Appendix I PIC24F Register Initializations Only applicable initialization registers and configuration bits are shown here Timer Subsystem PRI The timer period user configurable
11. SiRF Technology Inc Dec 2007 Online Available http www sparkfun com datasheets GPS NMEA 20Reference 20Manual Rev2 1 Dec07 pdf Accessed March 20 2010 33 Implementing File I O Functions Using Microchip s Memory Disk Drive File System Library Microchip Technology Inc 2008 Online Available http ww1 microchip com downloads en A ppNotes 01045b pdf Accessed March 23 2010 34 Calculate Distance Bearing and More Between Two Latitude Longitude Points Movable Type Scripts Online Available http www movable type co uk scripts latlong html Accessed March 24 2010 36 ECE 477 Final Report Spring 2010 Appendix A Individual Contributions A 1 Contributions of George Hadley Over the semester I completed the Preliminary PCB Layout Narrative and Patent liability analysis homework assignments which forced me to be well versed in issues related to the placement of the Gauntlet s components as well as infringement issues related to the Gauntlet s operation I also brought a number of valuable skills to the team including prior embedded system design experience printed circuit board layout experience soldering and physical construction experience and video filming editing experience Additionally I provided many of the tools the team used to excel in these areas which included a cordless power drill cordless rotary tool video camera and a book on programming the PIC24 micr
12. Spring 2010 The Foretrex while having a small very portable package does not need to withstand the force that the Gauntlet will due to the target consumers of the latter having to use the product while actually doing their winter sport activities The LCD screen will not be needed as the users will more likely need to look in front of them when the device is in use The package of the Gauntlet will be slightly larger to fit better onto the forearm and to keep all of the components inside safe from impact Figure 7 1 The Garmin Foretrex 301 7 1 2 Product 2 The Flaik Armband The Flaik Armband is designed for snowboarders and skiers just like the Gauntlet It also keeps track of its wearer s velocity GPS position and altitude 21 similar to the Gauntlet However unlike the Gauntlet which relays real time information to the user the Flaik relays information to a server in order to keep track of all of the snowboarders and skiers on the mountain as well as to record the users performance on the mountain The packaging for the Flaik is small about the size of a cellular phone and is worn on the upper arm The actual Flaik is in a plastic enclosure that is separate from the band itself as shown in Figure 7 2 below Unlike the Gauntlet the Flaik has no need for a human interface It only needs to relay information to a server and the user can access it later whereas the Gauntlet needs to send the information instantly Becau
13. TICON The timer control register TON 1 enabled TSIDL 0 continue operation in IDLE TGATE 0 no gated time TCKPS lt 1 0 gt 11 1 256 clock prescaler TSYNC 0 no external synchronization TCS 0 internal clock ADC Subsystem ANICONI Control Register 1 ADON 1 enabled ADSIDL 1 disable in IDLE mode FORM lt 1 0 gt 10 unsigned fractional output SSRC lt 2 0 gt 111 automatic conversion after sample ASAM 0 automatic sampling off ANICON2 Control Register 2 VCFG lt 2 0 gt 000 use Vdd and Vss as ref CSCNA 0 use CH1SA bits for channel select SMPI lt 3 0 gt 0000 interrupt after every conversion BUFM 0 buffer is 16 bits ALTS 0 use single multiplexer ANICON3 Control Register 3 ADRC 0 use system clock ADICHS Channel Select CHONA 0 use VR for negative input CHOSA lt 4 0 gt 00101 use ANS for positive input ADIPCFG Port Configuration PCFG lt 15 0 gt OxFFDF enable AN5 UART System UIMODE Mode Register UARTEN 1 enabled UFRZ 0 enable in debug mode USIDL 0 continue in IDLE mode IREN 0 disable IrDA RTSMD 1 simplex mode ALTIO 0 use normal pins UEN lt 1 0 gt 00 use only UITX and UIRX WAKE 1 wake up enabled LPBACK 0 loopback disabled I 1 ECE 477 Final Report Spring 2010 UISTA UIBRG SPI System SPkSTAT SPIxCON1 SPIxCON2 I2C System I2C1ICON RCIBRG ABAUD 0 no auto baud rate RXINV 0 RX idle state is 1 BRGH 0 low speed baud PDSEL lt 1 0 gt 00 8 bit no parity STSEL 0 one
14. as possible without having to replace it This is impossible in practice so a possible buy back program may be implemented so that the batteries can be recycled properly for monetary compensation Another way to increase the battery life is to indicate the time to recharge the battery to the user so as to maximize battery life Also instructions about battery disposal could be included in the user manual as there are ways to make the battery landfill safe 17 ECE 477 Final Report Spring 2010 Finally the packaging for the Gauntlet is in a non biodegradable plastic case Again the disposal of the case is of concern OKW Enclosures created the case from recycled plastics and therefore the plastic case is recyclable as well The buy back program mentioned above may also be implemented to motivate users to give their products to be recycled 7 0 Packaging Design Considerations Being designed for skiers and snowboarders the packaging of the Gauntlet needs to fulfill several requirements Because the design of the device is to make it wearable on the forearm the weight and size of the package were taken into consideration The material must be light enough that the device will not cause any strain on the user while they are engaging in their activities and small enough to fit comfortably over their arm without any problems Also due to the Gauntlet s intended use and target demographic the packaging must also be sturdy enough to
15. datasheet was used in calculations for the charge manager 16 PIC24 Ay Ci ar C2 ag no TL Parameter name Description Value Comments Ci Die Complexity 0 28 16 bit microcontroller TT Temperature Factor 0 29 T 50 C Digital MOS C2 Package Failure Rate 0 025 Hermetic SMT 64 pins TE Environment Factor 4 0 Ground Mobile TQ Quality Factors 10 0 Commercial product TL Learning Factor 1 0 In production for gt 2 years since 2008 Entire design Ap 1 812 MTTF 63 years VS1011E MP3 Decoder A Ci nr Co Te To TL Parameter name Description Value Comments Ci Die Complexity 0 56 16 32 bit core VSDP processor used 32 bit Tr Temperature Factor 0 29 T 50 C Digital MOS C2 Package Failure Rate 0 013 Hermetic SMT 33 functional pins used 36 pins TE Environment Factor 4 0 Ground Mobile TQ Quality Factors 10 0 Commercial product TL Learning Factor 1 0 In production for gt 2 years since 2005 Entire design Ap 2 144 MTTF 53 years 12 ECE 477 Final Report LTC3440 Buck Boost A C ap Co mg To AL Spring 2010 Parameter name Description Value Comments Ci Die Complexity 0 01 Linear less than 100 transistors TT Temperature Factor 58 Timax 125 C Linear C2 Package Failure Rate 0 0034 Hermetic SMT 10 pins TE Environment Factor
16. from both the GPS and from memory and relaying the information through the audio and visual components of the device so that in the worst case the Gauntlet will still lead the user back to a safe place 6 2 Environmental Impact Analysis The environmental impact of the Gauntlet is a major concern in designing that must be addressed before mass production The device is made up of many different components each of which must ideally follow a set of rules to be environmentally friendly The vast majority of components selected for the device are RoHS compliant which means that they do not contain any hazardous substances as outlined in the RoHS standard which includes mercury lead cadmium hexavalent chromium polybrominated biphenyls and polybrominated diphenyl ethers 17 16 ECE 477 Final Report Spring 2010 The manufacturing of the PCB releases toxic chemical into the environment and we use leaded solder to secure our parts Unfortunately there is no alternative to the manufacturing process In the future green PCB s may be looked into but for this project this could not be a concern due to there being no good alternative Lead free solder can be used as an alternative to the leaded solder but it was not a large concern of this project but there was none readily available for the design of the Gauntlet The LCD is the first concern in terms of the environmental impact of the Gauntlet where there was an actual design co
17. on the main code when problems came up I helped Jacob write a lot of the main code and then I focused on fixing certain problems that came up such as fixing the I2C interface when it wasn t appearing correctly on the oscilloscope correcting the navigation algorithm when latitude and longitude were switched fixing some of the functions when an incorrect number was displaying on the LCD and some bugs in the Menu System once it was implemented Apart from the main responsibilities given to me there were some more minor jobs that I had a hand in I was responsible for the Ethics and Environmental Analysis which I was able to do some research into when the time came concluding that our product was mostly green as far as electronics go I helped Kelli write much of the User Manual and in the process determined how our Menu System should work I also made the Team Logo one night in Photoshop which we eventually used on the poster A 3 Contributions of Jacob Champion My design component homework the design constraints narrative required me to research and select components for the Gauntlet My specific areas of research included the ECE 477 Final Report Spring 2010 selection of our accelerometer the ADXL345 our altimeter the SCP1000 D01 and our GPS the PMB 648 I balanced cost utility and ease of use for each of these selections the accelerometer and altimeter were finally chosen because they are both SPI based and th
18. one more SPI interface and fifteen more I O pins The ATX is also approximately 5 more expensive than the PIC which sells for four dollars Because both chips met our minimum requirements the PIC IC has a smaller package and one team member has extensive experience with PIC microcontrollers it was decided that the Microchip PIC will do nicely for the Gauntlet 3 3 Summary The Gauntlet does not perform time critical calculations so its peripheral requirements are modest a handful of general I O pins three SPI interfaces an I2C bus and a UART are all that are needed for the microcontroller to do its work Components were chosen for their small form factor low current consumption cold weather operation and ease of use Because of these design choices the Gauntlet can be used comfortably for long periods of time providing maximum enjoyment for the user 4 0 Patent Liability Analysis Key hardware features of the Gauntlet include GPS waypoint navigation an audio interface an accelerometer and altimeter and SD Card storage In addition the Gauntlet features a number of important software features including the use of GPS and accelerometer data for the calculation of slope grade and downhill velocity the use of accelerometer data for recording airtime and the conveyance of information to the user through the use of an audio interface There are a number of patent liability issues here such as patents issued for GPS navigation devices
19. outdoor activities This means that the device must be able to function fully while the user is skiing at a relatively high velocity down a snow covered slope While the activity itself carries risk to the user the Gauntlet must in no way be the cause of such risk An example would be if the audio malfunctioned and simply released a noise that would distract the possibly very concentrated user from avoiding the potential obstacles on a ski slope To mitigate this thorough testing of the audio circuitry and software will need to be conducted in order to make sure that whatever is released on the user s headphones will be exactly what the user wants to hear and that the output sound is of a reasonable pitch so that it doesn t distract the user Another example would be to design around the conditions that the Gauntlet will be in It is very likely that the user will fall and the Gauntlet will be put under a lot of stress and strain In this case our packaging must be durable enough to handle such impact and keep the components 15 ECE 477 Final Report Spring 2010 safe from harm This includes the strap that holds the device on the user s arm since the user will likely have a hard time keeping the Gauntlet on their arm as they perform their outdoor activities and a natural reflex is to try and catch the device when it falls This could cause the user serious injury if this happens during a run downhill Another example would be that the d
20. power down to 3 5 uA at 3 3V absolute pressure sensor with up to 9 cm of altitude resolution It communicates via a SPI bus and does all analog to digital conversions internally Conveniently it also houses an accessible onboard thermometer The MPXA6115 is an analog pressure sensor which uses significantly more current 4 mA and would require at least a 17 bit ECE 477 Final Report Spring 2010 ADC to get the resolution that the SCP1000 provides Its main selling point was its packaging whereas the SCP1000 is housed in an incredibly small circular package the Freescale chip is a much more manageable SSOP but the SCP1000 became the clear choice once a breakout board was discovered 3 2 2 Accelerometer The Bosch BMA150 4 and the Analog ADXL345 5 were excellent candidates for the onboard three axis accelerometer Both are low power 200 uA or below at 3 3V and interface to a microcontroller over SPI while providing high sensing resolution The ADXL345 has an advantage in that it provides free fall and motion interrupt support while using less power than the BMA150 Also the ADXL345 has an available breakout board solution whereas the BMA150 has an extremely small 3x3mm LGA package For these reasons we chose the former IC 3 2 3 Audio Decoder For the onboard audio decoder the main competitors were VLSI s VS1011e 6 and STMicroelectronics STAO13 7 Both chips are streaming MP3 decoders which operate on low voltage 3 3V an
21. the ability to turn the backlight on and off A decoupling capacitor and a few pull up resistors are required to configure the LCD circuit The tactile switches connect to the microcontroller through general I O pins and will be debounced in software 8 2 Hardware Design Narrative The microcontroller uses SPI I2C UART and interrupts to communicate with various subsystems General purpose I O pins are used to communicate with subsystems when SPI I2C or interrupts are not needed Appendix G provides a list of individual microcontroller pins and the external devices and pins to which they are connected Assignments were made after considering the characteristics of the microcontroller pins requirements of the external pins and location of pins for ease of routing The microSD card MP3 decoder accelerometer and altimeter communicate with the microcontroller using an SPI interface The PIC24 has three SPI units which can be remapped to various pins 9 The microSD card has a dedicated SPI interface to the microcontroller for the MISO CLK MOSI and CS The MP3 decoder also has a dedicated SPI interface to the microcontroller The SO SI SCLK xCS and xDCS were assigned near the reset and data ready pins The altimeter and accelerometer share the last SPI interface from the microcontroller because they do not need constant communication The SPI bus includes MISO MOSI and SCK The altimeter chip select data ready input trigger and power dow
22. the top of the case to allow pushbuttons and the LCD display to be accessible from the outside of the case At the end of the semester my considerable previous experience in video filming and editing due to some previous video projects allowed the team to create a professional looking video I performed all of the filming needed for the project and once that was done took care of capturing all of the footage to an external hard drive Finally all of the footage was edited together using Final Cut Pro based on suggestions the team provided for the film A 2 Contributions of Sean Ma At the beginning of the semester I was mostly a contributor to discussions and conceptual ideas I learned PADS so that I could support the team when we needed to construct the PCB but most of the work ended up going to George and Jacob I was able to contribute ideas and such and did some rerouting of traces with Kelli so that our PCB was more consistent I also was the main person in charge of researching the microSD card and how to interface with it so that we could use it for persistent storage One of my biggest contributions in the early weeks was in determining the packaging I was in charge of the packaging homework and so I did some research into enclosures that we could use and found the OKW Ergo Case Seeing the case as the best example of a wearable plastic enclosure I ordered a free sample of one and an eyelet set so that we could attach the st
23. ECE 477 Final Report Spring 2010 Kelli Hacker Team Members 1 George Hadley 2 Sean Ma 3 Jacob Champion 4 Kelli Hacker Technical content g j George Hadley Signature Signature Signature Signature Team 3 The Gauntlet Sean Ma Jacob Champion Date 5 07 10 Date 5 07 10 Date 5 07 10 Date 5 07 10 Design documentation Technical writing style Contributions Editing Comments ECE 477 Final Report TABLE OF CONTENTS Abstract 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 10 0 11 0 12 0 13 0 Project Overview and Block Diagram Team Success Criteria and Fulfillment Constraint Analysis and Component Selection Patent Liability Analysis Reliability and Safety Analysis Ethical and Environmental Impact Analysis Packaging Design Considerations Schematic Design Considerations PCB Layout Design Considerations Software Design Considerations Version 2 Changes Summary and Conclusions References Appendix A Individual Contributions Appendix B Packaging Appendix C Schematic Appendix D PCB Layout Top and Bottom Copper Appendix E Parts List Spreadsheet Appendix F FMECA Worksheet Appendix G Pin Assignments Appendix H PIC24F Memory Map Appendix I PIC24F Register Initializations Spring 2010 NY oQ N e e 18 21 25 27 32 33 34 B 1 C 1 D 1 E 1 G 1 H 1 I 1 ECE 477 Final Report Spring 2010
24. GPS and I trimmed the header After a few adjustments of wires inside the case I was able to close the case ECE 477 Final Report Spring 2010 Appendix B Packaging Emergency Mode DC Power In Pushbuttons Figure B 1 Gauntlet Package Design Isometric Figure B 2 Gauntlet Package Design Front B 1 ECE 477 Final Report Spring 2010 Figure B 3 Gauntlet Package Design Side Figure B 4 Gauntlet Package Design Top B 2 ECE 477 Final Report Spring 2010 Figure B 5 Final Packaging Isometric Figure B 6 Final Packaging Top B 3 ECE 477 Final Report Spring 2010 Appendix C Schematic woa A KO arcem Pushbuttons Group 3 The Gauntlet TME Sensors and User Interface Schematic Besedo Kaededonge 7 RELEASED lt Released By gt DATED Pease os Figure C 1 Sensor and User Interface Schematic C 1 ECE 477 Final Report Spring 2010 ov Group 3 The Gauntlet bn Audio Decoder el Stir Team 3 Save mel p e OC By gt V1 elaared oy gt PES EE Figure C 2 Audio Decoder Schematic C 2 ECE 477 Final Report Spring 2010 MP3 Header He 0 H Oscillator gE hik Group 3 The Gauntlet ARE and oy Interface oan Ot me je DATED Schematic Team 3 Drawn Date gt en et er en letode gt B B RELEASED Wenne je SI EE Figure C 3 Microcontroller Schematic C 3 ECE 477 Final Report Spring 2010 Fuel Gau
25. able to operate in below freezing temperatures It must also have low enough power consumption to last for ten or more hours on a single charge To meet these constraints surface mount components with low current consumption and the ability to operate at temperatures at or below 20 C were chosen 8 1 Theory of Operation 21 ECE 477 Final Report Spring 2010 The Gauntlet contains several functional subsystems These are the microcontroller power memory environmental sensors audio and user interface All subsystems operate at 3 3 V to simplify circuitry eliminating the need for converters or separate power connections and save power and space All circuitry is located on one PCB 8 1 1 PIC 24 The design utilizes a PIC24FJ256GA106 microcontroller which in turn uses an external 12 MHz oscillator An external oscillator was added to help ensure good communication with the GPS which uses UART and to increase accuracy of communication with other subsystems The 12 MHz rate is fast enough to handle all the clock speeds needed for various subsystems in the Gauntlet The PIC24 communicates with and controls all peripherals A header is attached to programming pins to enable in circuit programming of the microcontroller 8 1 2 Power Regulation and Monitoring The Gauntlet is powered by a 2000mAh lithium polymer battery with a nominal voltage of 3 7 V and a discharge cut off voltage of 2 75 V 24 The battery is regulated by the LTC3440 Buck Bo
26. and Z accelerations is read via the SPI interface The absolute battery voltage is read using a single ADC sample conversion a maximum 10 bit value of Ox3FF corresponds to the maximum battery voltage of 4 2 volts The charge counter circuit works via an interrupt system When a discrete quantity of charge equal to 1 100 of the battery s nominal capacity passes through the charge counter an interrupt pulse is sent to one of the pins on the PIC Another pin is pulled high or low depending on the polarity i e charge or discharge of the count The interrupt handler then either adds or subtracts one from the charge count which starts at 23436 This provides a fairly accurate estimate of the charge percentage remaining in the battery Once a second the GPS sends NMEA sentences at 9600 baud to the microcontroller 32 The UART handler needs to move these sentences to an internal buffer and then notify the main loop when a buffer fills so that it can be parsed The sentences are parsed for their latitude longitude information the current speed over ground and the heading of the user These values are then stored in fixed point format for use by the calculation block 29 ECE 477 Final Report Spring 2010 10 6 2 MicroSD Interface The 2GB microSD card was formatted with a FAT16 file system to allow it to be easily loaded with MP3 samples from a personal computer Microchip 33 provides a FAT16 library for use with the PIC24F so we decided
27. and so we took advantage of that for the prototype 20 ECE 477 Final Report Spring 2010 Figure 7 3 The OKW Ergo Case M 7 3 PCB Footprint Layout The final PCB layout is in Appendix D As can be seen there is a lot of room for components on the board which must fit within the dimensions of the Ergo Case 23 suggests a size of about 128mm x 72mm 5 03 x 2 83 not including screw mounts Most of the devices determined in Section 3 are surface mount devices The PIC24FJ256GA106 microcontroller and the VS1011E L MP3 decoder chip are both quad flat pack surface mount devices whereas the LTC3440 Buck Boost Regulator LTC4150 Battery Monitor and the MCP73811T Charge Management IC are all SOIC devices The microSD card slot is also surface mounted though all of the pin mounts are on one side The rest of the components will require header pins The ADLX345 Accelerometer and the SCP1000 Pressure Sensor both come with breakout boards and so require header pins in order to connect to the main PCB The GPS module will connect to the board via ribbon cable so header pins are needed for that as well and the LCD and Battery Pack is not be mounted on the board 8 0 Schematic Design Considerations The Gauntlet is intended to be worn and used for several hours at a time in remote areas and below freezing temperatures which creates several constraints It needs to be small enough to wear comfortably on the arm and all components must be
28. as responsible for writing the Hardware Design Narrative and created the preliminary schematic in PADS Logic I collaborated with my teammates to get the information for the narrative and created a spreadsheet to keep track of pin assignments as they were made This spreadsheet was updated throughout the semester as changes were made and was extremely useful in several different stages of design I completed the preliminary schematic and was a significant contributor as changes were made throughout the semester While the PCB was being designed I assisted in the grouping of parts into functional blocks and the placement of blocks to ease routing Jacob Sean and I spent many hours rearranging the PCB to create cleaner routes and large power traces in addition to uniform A 5 ECE 477 Final Report Spring 2010 ground planes I found a PCB layout guide for the MP3 decoder which led us to arrange passives and traces carefully and to isolate the circuit as much as possible from other parts to avoid noise entering the circuit Once the PCB arrived I helped check it for obvious errors and connectivity issues George soldered the surface mount parts but I assisted by organizing all the passive components and keeping track of schematic connections while he put them on the board I helped test and debug most major functional blocks of the circuit including power microcontroller and audio circuitry When we discovered issues with our fuel gauge I wor
29. ating a critical reliability issue 5 1 Reliability Analysis Components in the Gauntlet are most likely to fail due to either complexity or heat The most complex parts are the PIC24FJ256GA106 microcontroller and the VS1011E MP3 decoder The PIC24 is a complex component with 64 pins and the VS1011E is a complex component which includes a DSP processor and a digital to analog converter in addition to 48 pins 33 of which are functional The LTC3440 buck boost converter and MCP73811 charge manager will have to dissipate the most power and will be the hottest components on the Gauntlet making them more likely to fail The Military Handbook Reliability Prediction of Electronic Equipment 14 was used to calculate the number of failures per million hours Ap and mean time to failure MTTF for each component The microprocessor model was used to analyze the PIC24 and the VSIOIIE The 11 ECE 477 Final Report Spring 2010 average junction temperature of the PIC24 was determined to be 50 C from the datasheet 9 The VSI1011E is an MP3 decoder but it contains a 16 32 bit DSP so the model of a 32 bit microprocessor was used for die complexity 6 Linear microelectronic models were used to analyze the LTC3440 and MCP73811 Because the LTC3440 might be operating at high temperatures the maximum junction temperature of 125 C was used to determine the temperature factor zr 15 A junction temperature of 105 C found on the MCP73811
30. ator would be added to the PCB for the VS1011e since that frequency provides the best performance 6 The charge counter would be attached to the battery instead of the power rail eliminating several of the problems we had over the semester The PIC24F ENVREG pin would not be left floating instead it would be connected to power to allow the PIC24F to correctly power on On a more minor note a ground plane would be added to the buck boost circuitry to reduce switching noise at higher current draws On a functionality level the Gauntlet would utilize a Kalman filter for its altitude reading combining input from the GPS and the altimeter to reach a nearly noise free result This would make our velocity calculation much better We would research the PMB 648 s static navigation mode in order to disable it and allow slightly more noisy waypoint updates at slow walking speeds An optimal path algorithm for emergency mode would search the waypoint list and eliminate loops in the user s path to guide them back to the safe point more quickly Finally on a machining and packaging level we would machine the package to fit the internal components more closely This would include machining holes in the PCB to allow wires to travel from one side of the case to the other as well as adding appropriate spacers to the mounting screws for the PCB We would also seal the package to make it watertight and provide protection in the event of a fall into snow
31. connection of change has 0 SCL or SDA pins random values internal error ECE 477 Final Report Appendix G Pin Assignments Spring 2010 Microcontroller Pins Pin Connect to External Device RP21 RG6 4 GPS TTL_Rx GPS 2 RP26 RG7 5 GPS TTL_Tx GPS 1 RP19 RG8 6 Alt DRDY Alt 7 MCLR 7 Program Header Pheader 1 VSS 9 DGND VDD 10 3 3V AN5 RP18 RB5 11 Battery AN4 RP28 RB4 12 Alt CSB Alt 6 AN3 RB3 13 Acc CS Acc 3 AN2 RP13 RB2 14 Alt SCK Alt 3 Acc SCL Acc 8 AN1 RP1 RB1 15 Alt MOSI Alt 4 Acc SDI Acc 7 ANO RPO RBO 16 Alt MISO Alt 5 Acc SDO Acc 6 AN6 RP6 RB6 17 PGC header Pheader 4 AN7 RP7 RB7 18 PGD header Pheader 5 AVDD 19 3 3V AVSS 20 AGND AN8 RP8 RB8 21 Acc Int1 Acc 4 AN9 RP9 RB9 22 Acc Int2 Acc 5 VSS2 25 DGND VDD2 26 3 3V AN13 RB13 28 SD DAT1 SD 8 AN14 RP14 RB14 29 SD MISO SD 7 AN15 RP29 RB15 30 SD CLK SD5 RP10 RF4 31 SD MOSI SD 3 RP17 RF5 32 SD CS SD 2 RP16 RF3 33 SD DAT2 SD 1 RP30 RF2 34 LCD BACK LCD 4 RP145 RF6 INTO 35 LCD RST LCD 1 SDA1 RG3 36 LCD SDA LCD 3 SCL1 RG2 37 LCD SCL LCD 2 VDD 38 3 3V OSCI CKLI RC12 39 XTAL IN OSCO CLKO RC15 40 XTAL OUT VSS 41 DGND RP4 RD9 43 MP SO MP 30 RP3 RD10 44 MP SI MP 29 RP12 RD11 45 MP SCLK MP 28 RP11 RDO 46 MP DREQ MP 8 G 1 Spring 2010 ECE 477 Final Report RC13 47
32. croSD card Sean and I both contributed equally to the GPS communication and navigation portions of the assignment Completing these PSSCs involved engineering and implementing a trigonometric lookup table to convert a difference in latitude and longitude into a distance measurement as quickly as possible This allowed the Gauntlet to efficiently store waypoints to a persistent stack file we created which automatically saves and maintains the path the user has taken to his or her current location We also created the final user interface for the Gauntlet which is a menu based system that allows the user to easily change preferences and operating modes while also providing useful information about the user s activities A 4 Contributions of Kelli Hacker During the conception and early design portion of the project I focused on the audio circuitry and found an appropriate chip for coulomb counting I researched several different chips that fit our constraints of purpose size cost and operating conditions I found a variety of text to speech and decoding chips and researched their constraints and sound quality After comparing several candidates I selected the VS1011E a well documented chip which can decode MP3 and several other formats and it does not need an external digital to analog converter or audio amplifier I also looked at documentation from other teams who used coulomb counters and found the fuel gauge that we used in our design I w
33. culties placing the decoupling capacitors close to the microcontroller pins The microcontroller requires five pins for device programming These pins are broken out as an onboard header and the length of these traces needed to be minimized to mitigate programming errors 9 5 PCB Layout Design Considerations Power Supply The power supply for the Gauntlet system consists of several components the DC power barrel jack the Li Ion charger IC the fuel gauge IC and a buck boost converter chip The DC barrel jack needed to be located on the right side of the PCB to allow for easy access to the exterior of the packaging The Li Ion charger IC requires input and output capacitors as well as a programming resistor to be located nearby 16 Additionally digital ground as well as the battery power and digital power planes needed to be located near the Li Ion charger with vias to improve heat dissipation 16 According to the device s data sheet the charger IC must be located as close to the battery as possible to minimize power losses 16 Traces are fairly low resistance however so locating the charging IC within an inch of the battery leads should be sufficient for the purposes of this project In addition to the charger IC the battery fuel gauge and the buck boost regulator ICs have a number of important layout considerations In particular a current sensing resistor with a Kelvin connection should be placed near the IC to provide accurate curre
34. d current 50 mA for the VS1011e 30 mA for the STAO13 In addition to MP3 decoding the VS1011e can also decode WAV files giving us some added flexibility It also houses an on chip headphone driver which reduces the amount of circuitry needed to present audio to the user The STAO13 in contrast requires an off chip DAC Because both are evenly priced and the VS101 le is a one chip solution we chose the VS101 1e despite its higher current draw 3 2 4 GPS Parallax s Polstar PMB 248 and PMB 648 8 were the only two GPS modules that received true attention from our group In addition to being reasonably priced and fairly low power they both require no external circuitry or RF design and one team member has experience working with Polstar modules The PMB 648 is slightly more expensive but its chipset is more reliable and provides faster fix times so we chose it over its brother 3 2 5 Microcontroller The two microcontrollers examined by our team were the Microchip PIC24FJ256GA106 9 and the Atmel ATXMEGA256A1 10 Both are clocked at a maximum of 32 MHz though the PIC has half the throughput of the ATX have 256K of Flash and 16K of RAM and are ECE 477 Final Report Spring 2010 operated at low current Both meet the peripheral and general purpose interfacing requirements stated above and each microcontroller has floating point libraries available for it The PIC is a 16 bit processor while the ATX is an 8 bit device but the ATX gives
35. d two floating point additions and subtractions Instead a fixed point approximation is used which utilizes multiple trigonometric lookup tables After finding the horizontal distance the vertical distance can be computed by simple subtraction and presented to the user To calculate the exact direction to a waypoint a much more complicated function is needed the bearing is given by atan2 sin long2 long cos lat2 cos lat1 sin lat2 sin lat1 cos lat2 cos long2 long1 34 This is incredibly uC intensive so a simpler arctangent approach is used under the simplifying assumption that the earth is flat This reduces the trigonometric requirement from seven calls to one for the arctangent itself and is close enough for the Gauntlet to navigate correctly up to distances of a few miles 30 ECE 477 Final Report Spring 2010 10 6 4 Action on Input The microcontroller s reaction to the accelerometer data is simple If all three axes of acceleration are sufficiently close to zero for a sufficiently long amount of time the PIC should record a jump and note the time otherwise the PIC should stop a jump in progress and record the total airtime If the magnitude of the acceleration spikes suddenly the PIC should mark a crash condition These conditions can then be communicated to the user Decisions on waypoint storage are distance based If the distance to the last saved waypoint measured by the sum of the squares of each axi
36. e I used references such as the PIC24F datasheet manual and online tutorials to begin writing a basic polling loop for the microcontroller I researched and chose the peripheral initializations which included UART SPI I2C and interrupt based communication and mocked up the overall software framework for the Gauntlet with stub functions that could be implemented one at a time to enable functionality I wrote the audio driver for the Gauntlet which takes numbers and phrases off of the microSD card queues them in play order and streams them as quickly as possible to the MP3 decoder while still allowing the user to interact with the UI I also successfully enabled the accelerometer after a prolonged debugging period which allowed the Gauntlet to make airtime measurements This process involved hardware debugging for the SPI interface followed by manual testing and tweaking of freefall and activity interrupt parameters to ensure that jumps were correctly recognized by the microcontroller I used an online altitude table and a cubic regression function to allow the microcontroller to convert the pressure reading from the ECE 477 Final Report Spring 2010 SCP1000 into an altitude measurement which is saved with a GPS waypoint to provide an overall picture of a user s path During our microSD integration phase I discovered and fixed bugs in Microchip s SD library which prevented the microcontroller from correctly formatting and reading the 2 GB mi
37. e chosen packaging for the project 9 1 PCB Layout Design Considerations General There are a number of important general considerations that must be taken into account The PCB layout is separated into a number of functional groups which include the battery charge regulation and monitoring group the audio interface the SD interface sensors and the core microcontroller This provides isolation which helps reduce noise in the PCB design To minimize PCB production errors and noise problems right and acute angles are avoided at all costs Noise and thermal performance of certain components particularly the inductor and IC in the boost buck regulator circuit are improved considerably through the incorporation of significant power and ground planes beneath and around those components Additionally the microSD card features a keep out region in which no traces can be routed 28 This region is a relatively small region under the card and has no impact on the placement of other system components Finally noise in the circuit needs to be decoupled from all ICs using decoupling capacitors 9 2 PCB Layout Design Considerations Packaging 25 ECE 477 Final Report Spring 2010 In order to fit inside the chosen casing for this project the board was limited to a maximum size of 126mm x 88mm fitting snugly inside the case which is 150mm x 100mm 23 From this initial size small cutouts needed to be made from 2 of the corners to leave ro
38. ed when a failure could result in major irreparable circuit damage The failure rate of medium criticality failures should be below 1 failure in 10 hours of operation Low criticality covers failures which do not cause harm to the user or irreparable circuit damage Failure rates should be below 1 failure in 10 hours of operation for a low criticality failure 53 Summary The Gauntlet is a reliable and safe device overall However a few design changes may need to be considered to increase safety and reliability in future iterations Adding a low pass filter to reduce switching noise to the analog comparator or changing resistor values to increase the safety margin will decrease the likelihood of battery failure increasing the safety of the user Currently any device failure while unlikely may render the Gauntlet useless Reliability may be increased by adding redundancy and increasing the robustness of the design However the current design should be reliable for several years 6 0 Ethical and Environmental Impact Analysis The design of the Gauntlet brings about several ethical and environmental issues that need to be addressed before being put to market such as the possibly environmentally harmful 14 ECE 477 Final Report Spring 2010 manufacturing of the components the non biodegradable nature of the device and the implications of its functionality 6 1 Ethical Impact Analysis There are many ethical implications for the Gaunt
39. een the PIC24 and the individual sensors could be accessed for debugging 8 1 5 Audio The VS1011E Audio Decoder chip decodes MP3 files and drives the stereo earphone jack to send audio to the user The microcontroller sends MP3 data through an SPI interface at 1 MHz which is fast but below its maximum rate of 3 5 MHz 6 The VS1011E is used in native mode in which the chip select is used to synchronize data rather than in compatibility mode in which a synchronizing signal must be generated 6 General purpose IO pins which are not used are pulled down with 100 kQ resistors The xDCS chip select pin which can be used for the data interface is pulled high so that the shared chip select setting can be used or the chip select can be controlled by the microcontroller 6 Resistors and capacitors 23 ECE 477 Final Report Spring 2010 are placed on the audio output to provide ESD protection from the audio jack 6 Headers are available for signals traveling between the VS1011E and the microcontroller 8 1 6 User Interface The Gauntlet s user interface consists of the NHD C0220BiZ FSW FBW 3V3M LCD screen and three tactile switches The LCD screen uses an 2C interface to communicate with the microcontroller at its maximum frequency of 400 kHz and it relays information to the user 27 The backlight of the LCD is controlled by a switching transistor connected to the microcontroller to conserve power and give the microcontroller
40. er and given its outdoor winter application the junction temperature could easily be lower lowering the overall failure rate In addition the worst case junction temperature was used in calculations for the LTC3440 Also a die complexity for between 1 and 100 transistors was used although the LTC3440 model shows four transistors 13 ECE 477 Final Report Spring 2010 which would lower complexity considerably 15 The LTC3440 needs to dissipate power so adding a heatsink may need to be considered to increase safety and reliability The MCP73811 model includes six transistors even though the die complexity value used is for up to 100 transistors 16 Lowering this complexity value may increase reliability and adding a heatsink may be considered for the linear charger 5 2 Failure Mode Effects and Criticality Analysis FMECA The main functional blocks of the Gauntlet schematic are shown in Appendix C The functional blocks are the power microcontroller audio and sensors and user interface The memory is included in the microcontroller functional block A Failure Mode Effects and Criticality FMECA analysis was performed for each functional block and is shown in Appendix F Criticality levels of high medium and low are used in the FMECA analysis High criticality is reserved for when a failure could cause harm to the user and its failure rate should be below 1 failure in 10 hours of operation Medium criticality is us
41. erefore can be multiplexed if the microcontroller has a limited number of SPI connections and they are available in easy to solder breakout boards Upon receiving the altimeter and GPS I used a Texas Instruments MSP430 and a serial connection to test their functionality and ensure that the microcontroller at the heart of our project would be able to communicate with them properly I assisted the team in designing the analog and power circuitry for the Gauntlet This specifically included designing and choosing components for the LCD backlight controller so that the PIC24F did not need to source 20 mA out of a control pin which would have put it severely out of tolerance as well as choosing essential components such as the DC barrel jack the headphone jack and a high quality inductor for the buck boost converter I researched the lithium polymer battery we selected and discovered that it would require protective circuitry to prevent an undervoltage condition I then assisted the team in designing an analog shutdown for our buck boost converter in an undervoltage situation to prevent user injury During the PCB layout portion of our project I assisted George in creating accurate part footprints for our components I also assisted with a cleanup of the PCB layout which rearranged our power circuitry our audio converter and the sensor layout to facilitate debugging and reduce noise My primary responsibility for the Gauntlet was embedded softwar
42. evice must work under moist conditions This can be accomplished using some proper sealing of the electronic components in the case The most crucial function on the device that needs attention is the emergency mode The Gauntlet s emergency mode is supposed to lead the user back to a safe point by retracing a path that has been recorded before This function is put in so that when the user is lost they can activate this mode as a guide back to safety At this point the user will be entirely dependent on the Gauntlet to perform its function fully and reliably This has many implications to the design The algorithm used to trace a path back to the safe point must be solid enough so that it can reliably retrace its steps back to the starting point It should under no circumstances lead the user away from safety The device must remain low power enough for the battery to last otherwise the Gauntlet may simply stop working in the middle of leading the user back to safety Several components will play a major role in the emergency mode The GPS will determine current position and heading the microSD card will be where the waypoints are stored and the LCD and audio will be the main interfaces to tell the user where to go Because the user is depending on the device to lead them to safety each component needs to be in full working condition under virtually any circumstance Extensive testing under extreme conditions must be done on retrieving information
43. ge Buck Boost Undervolt Protection acu er Group 3 The Gauntlet 3 er Group 3 The Gauntlet Gauntlet Power Connections DRAWN Drawn Date gt Schematic CHECKED DATED lt Checked By gt Checked Date gt Eer z oje v B DATED Figure C 4 Power Schematic C4 ECE 477 Final Report Spring 2010 Appendix D PCB Layout Top and Bottom Copper Jo up et vind i C16 The Gauntl i Spring 201 Jacob Champian George Hadley Kelli Hacker Seon Ha gountlet_final_beta pcb Fri May OF 13 18 23 2010 Figure D 1 Top Copper D 1 ECE 477 Final Report Spring 2010 gountlet_final_beta pcb Fri May OF 13 20 08 2010 Figure D 2 Bottom Copper D 2 ECE 477 Final Report Appendix E Parts List Spreadsheet Spring 2010 Vendor Manufacturer Part No Description Unit Cost Qty Total Cost Sparkfun Union Battery PRT 08483 2000 mAh Lithium Polymer Battery 16 95 1 16 95 Parallax Polstar PMB 648 GPS Module 34 99 1 34 99 Sparkfun VTI SCP1000 D01 SPI Pressure Sensor Breakout Board 34 95 1 34 95 Sparkfun Analog ADXL345 SPI 3 Axis Accelerometer Breakout 27 95 1 27 95 Sparkfun VLSI VS1011E L MP3 Streaming Decoder 19 95 1 19 95 Microchip Microchip PIC24FJ256GA106 16 bit 32 MHz Processor 3 98 1 3 98 Digi Key AVX Corporation 045138008010890 MicroSD Connector 3 86 1 3 86 Radio Shack SanDisk P SDU2GB FS BB 2GB MicroSD Card
44. hbuttons Software bug Constant change Observation Low stuck at 0 internal of settings loss microcontroller error of functionality ECE 477 Final Report Spring 2010 Audio Subsystem Failure Failure Mode Possible Causes Failure Effects Method of Criticality Remarks No Detection Cl MP3 decoder Bypass capacitor Audio does not Observation Low receives lt 3 3 V shorts operate C2 MP3 decoder Decoder receives Audio does not Observation Low Repairable chip damaged ESD output operate capacitors short C3 SPI pins stuck at Shorted trace Loss of Observation Low Oor 1 internal error communication with microcontroller loss of new audio C4 Audio output Internal error Loss of audio Observation Low Volume is a different pins stuck at 1 or shorted trace possible function so no extra 0 annoying audio output loud noises should be emitted ECE 477 Final Report Spring 2010 Sensors and User Interface Subsystem Failure Failure Mode Possible Causes Failure Effects Method of Criticality Remarks No Detection D1 Pushbutton stuck Switch shorted Loss of Observation Low Very little loss of high communication functionality with user device set at defaults D2 Pushbutton stuck Switch broken Constant change Observation Low low of settings loss of functionality D3 SCL or SDA Short or LCD does not Observation Low pins stuck at 1 or dis
45. ion Recommended 4 3 1 Route Based on Distance Patent No 7 627 423 10 ECE 477 Final Report Spring 2010 This patent uses terminology and examples that suggest it is intended for use as a personal running device but could be considered infringing with the Gauntlet on the basis of doctrine of equivalents That said the patent may be able to be challenged for being trivial as it appears to be a logical extension of traditional GPS technology Otherwise however the patent may need to be licensed 4 3 2 Navigation Device Method and Program Patent No 7 565 240 The potential for patent infringement certainly exists with this patent which covers a broad and overreaching field of technology infringeable under doctrine of equivalents That said however the patent could be challenged on the grounds that it is not novel based on prior art in the field Failing at this however the patent may need to be licensed 4 3 3 Flaik Armband Potential for patent infringement seems unlikely based on current knowledge so no current actions need to be performed to minimize patent infringement liability 5 0 Reliability and Safety Analysis The safety of the user is a critical issue User safety could be compromised by proximity to the device because the user is more likely to be seriously injured if something happens to the Gauntlet and by the use of lithium polymer batteries Functionality is dependent on communication with several sensors cre
46. ise explosion on buck boost output charger fails A4 Battery Charger fails and Possible battery Observation High overvoltage short circuits explosion ECE 477 Final Report Spring 2010 Microcontroller Subsystem Failure Failure Mode Possible Causes Failure Effects Method of Criticality Remarks No Detection Bl Microcontroller Bypass capacitor Microcontroller Observation Low receives lt 3 3 V shorts will not operate no functionality B2 External Failure of individual No audio output Observation Low Internal oscillator oscillator fails components errors more takes over if external likely in LCD signal is missing communication B3 Microcontroller Loss of Loss of Observation Low Loss of functionality stuck in loop communication with functionality but repairable sensors B4 SPI or 2C Pins Software bug Loss of Observation Low stuck at 0 or 1 internal communication microcontroller error with sensor LCD audio B5 Interrupt pins Software bug Loss of free fall Observation Low stuck internal battery microcontroller error information B6 Altimeter CS or Software internal Loss of Observation Low Accelerometer microcontroller error communication CS stuck with 1 device B7 Pushbuttons pins Software bug Loss of Observation Low Very little loss of stuck at 1 internal communication functionality microcontroller error with user device set at defaults B8 Pus
47. ked with a circuit on a bread board to test our circuit design I determined that the individual circuit design did not appear to be a problem once one connection was fixed because the circuit worked on the bread board Then I did connectivity checks on every connection in the circuit on the PCB but did not find any specific errors I was also involved in several testing and debugging sessions with the fuel gauge circuit until the problem was resolved Once most of the hardware was assembled and tested I became involved in full system tests and debugging I helped find a few minor software issues and tried to learn how the software worked I helped with the initializations of the MP3 decoder and helped test its functionality Sean and I developed a menu system for our project to make it more user friendly and wrote most of the first draft of the user manual I helped test the GPS location and navigation algorithms and helped film and edit two different versions of our PSSC video I also wrote the Safety and Reliability Analysis paper and researched several different components which are most likely to lead to system failure I analyzed these components in the reports and calculated their Mean Time To Failure I also completed a FMECA analysis of our system I made a few contributions to packaging I added buckles and adjustable elastic straps to the Gauntlet casing to make it wearable I also determined that the SPI bus header was interfering with the
48. let that need to be addressed before it can be marketed The first is that the device must be safe for the average user to carry around and use as covered in the Reliability and Safety Analysis As noted in the aforementioned analysis the Gauntlet is a relatively safe device overall with most of its components being low power with not much impact on the user so the prime example of a possibly harmful component would be the lithium polymer battery An under voltage of the battery such as from the battery discharging too much could cause it to expand and possibly explode which would cause injury to the user An over voltage such as from a short circuit somewhere in the board could result in fire and an explosion which would also cause injury to the user Given these highly critical problems aside from the precautions mentioned in the previous report all of the operating conditions that the Gauntlet will likely be exposed to must be tested so that this event is virtually impossible For further preventative measures warning labels will be put into the user manual and on the device itself to prevent users from improperly using the device For example we would warn the user not to store the device in an extremely hot environment and to only charge the device using the given DC power jack as a voltage that is too high may burn the board or cause the aforementioned explosion The Gauntlet is meant to be a helpful tool for its users to bring for their
49. ller using an SPI interface A FAT16 file system was used and libraries provided by Microchip were used as drivers The microSD clock rate is controlled solely by the Microchip driver and adapts itself to the specific card being used The maximum clock rate for the microSD is 6 MHz or half the clock rate of the microcontroller A microSD card is used rather than an SD to minimize the footprint on the PCB 8 1 4 Environmental Sensors The Gauntlet uses a GPS unit a combination altimeter and thermometer and an accelerometer to sense its environment The GPS unit used is the Parallax PMB 648 High Sensitivity GPS Module which has a small footprint and low power consumption It communicates with the microcontroller on a serial connection using NMEA protocols at a baud rate of 9600 which is twice the standard rate but in the midrange of allowable rates 26 Information sent to the microcontroller includes current position altitude and velocity this information is used in calculations and in saving waypoints The SCP1000 Absolute Pressure sensor functions as an altimeter and thermometer for the Gauntlet It communicates with the PIC24 as an SPI slave at a clock frequency of 500 kHz 2 The ADXL345 Three Axis Digital Accelerometer sends data to the microcontroller using an SPI interface with a clock frequency of 500 kHz to make communication simpler because the altimeter and accelerometer will share an SPI bus 5 Headers were placed so signals betw
50. mputing device includes a global positioning system GPS receiver a processor a memory in communication with the processor a display in communication with the processor and memory and program instructions storable in memory and executable by the processor to receive a distance input and to generate a running route that begins and ends at a starting location and to receive location information from the GPS receiver to track the device along the running route wherein the running route has a length substantially equal to the distance input and is generated based on a selectable set of criteria and a selectable rating factor associated with a particular criteria and wherein the running route and device location are graphically represented on the display Claim 23 The system of claim 9 wherein the device is a portable handheld device attachable to another physical object Claim 25 The system of claim 24 wherein the training log includes elevation information associated with the running route 4 1 2 Navigation device method and program 12 Patent No 7 565 240 Date Filed November 28 2005 ECE 477 Final Report Spring 2010 Condensed Abstract The patent describes a navigation device capable of storing user selectable waypoints and using waypoint information to guide the user from an initial waypoint to a destination waypoint Key Claims Claim 1 A navigation device for providing guidance from a user s current l
51. n pins were placed near one another The accelerometer chip select and configurable interrupt pins were placed near one another The microcontroller s dedicated I2C pins used LCD signals SDA and SCL The PIC24 has five interrupt capable pins and three interrupts are used in the final product The INT pin for the coulomb counter allows instantaneous charge to be determined The accelerometer s INT1 and INT2 interrupts are used to detect free fall and the end of free fall Serial communication with the GPS uses remappable pins 24 ECE 477 Final Report Spring 2010 8 3 Summary The main circuit design constraints of the Gauntlet are small size low power consumption and the ability to work at 20 C The main subsystems are the microcontroller the power regulation and monitoring the flash memory the environmental sensors the audio and the user interface The GPS accelerometer altimeter and coulomb counter send information to the microcontroller which processes it stores some in memory and sends some to the MP3 decoder which sends audio information to the user Communication interfaces include SPI I2C interrupts and general I O 9 0 PCB Layout Design Considerations The Gauntlet utilizes a single PCB that is stored inside the forearm mounted casing Primary layout concerns for this PCB include the routing complexity of the microcontroller and noise reduction on the sensor traces as well as ensuring that the PCB fits inside of th
52. nal GPS for running and training purposes and is in this way fundamentally different from the Gauntlet The possibility for patent infringement may exist here and precautionary steps should be taken to minimize patent infringement liability 4 2 2 Navigation Device Method and Program Patent No 7 565 240 This patent appears to lay out the framework for a standard navigational device and the Gauntlet seems to infringe on this patent in a number of ways such as by saving waypoints to memory and guiding the user from one waypoint to another This patent appears to be written for vehicular navigational devices such as Garmin GPS units that have become ubiquitous in many cars Nonetheless potential for patent infringement does exist here and action may need to be taken to minimize patent infringement liability 4 2 3 Flaik Armband The Flaik armband is a commercial product though no patents related to the device are known at this time Both the Gauntlet and the Flaik share certain fundamental characteristics such as the use of a GPS unit in a wearable form factor and the application to winter snowsports However aside from this basic similarity the systems are not particularly alike the Flaik adding in radio tracking capability to track users of the armband while the Gauntlet has an audio interface to communicate information to the user Therefore it is believed that infringement is unlikely as the use of GPS is in the public domain 43 Act
53. nsideration A chemical known as Nitrogen Trifluoride NF3 is used during the manufacturing of LCD displays Nitrogen Trifluoride is considered a missing greenhouse gas and is approximately 17 000 times more potent than CO as a contributor to global warming and will stay in the atmosphere for an estimated 550 years 18 Given time a more environmentally friendly LCD may be used as a replacement but such an LCD has not yet been found considering that NF3 as a chemical is already an improvement over its predecessor perfleurocarbon another potent greenhouse gas which will stay in the atmosphere for over 10 000 years 18 Thus there are currently no better alternatives to this chemical in the manufacturing of the LCD The Gauntlet is mostly low power and uses a small rechargeable battery so during the use of the device there will be very little environmental concern The device in full use will consume approximately 0 84W of power at maximum voltage 4 2V and current 200mA which will not be significant even when charging Another possible concern is the battery The battery in the Gauntlet is a rechargeable Lithium Polymer battery Although for the most part environmentally friendly if the battery is not disposed of properly i e thrown into a landfill and incinerated it could prove hazardous to the environment 19 The best way to prevent this that can be done at the prototyping stage is to make sure the battery lives for as long
54. nt readings for the IC 25 Connections are also be minimized and a capacitor needed to be placed close to the device to ensure optimal performance 25 The buck boost regulator requires power and ground planes to be placed near the IC with vias to improve thermal dissipation 15 Also high current traces connected to the regulator do contain any bends to minimize noise and resistive losses 15 10 0 Software Design Considerations 10 1 Memory Constraints The PIC24F uses a modified Harvard architecture which utilizes separate memories and busses for program space implemented in Flash and data space implemented in RAM 9 27 ECE 477 Final Report Spring 2010 Appendix H shows the memory maps for both The variant of PIC used in the Gauntlet is able to store approximately 87 000 instructions in program space This is plenty of room for the microcontroller s code What is of primary concern is the data RAM although there are 16 KiB of it available to the PIC24F the first few KiB will be needed for the software stack The MPLAB IDE defaults to a stack size of 6 KiB this is an appropriate maximum value given the functions which are called during operation This leaves a minimum of 10 KiB to store working variables data structures and the MP3 buffer for transferring audio from the microSD card to the MP3 decoder Even if all of this space were used for sample buffering just over a second of audio could be fully buffered at a bit
55. ntly far apart to prevent space conflicts between the boards 9 4 PCB Layout Design Considerations Microcontroller The microcontroller utilized by the Gauntlet design is a PIC24FJ256GA006 which is being utilized in a 64 pin QFP package 9 A vast majority of these pins are utilized by the Gauntlet design and as such routing about the microcontroller was difficult To ease the routing process the microcontroller needed to have large amounts of board space allocated about it Also subsystems on the microcontroller needed to be positioned such that the number of electrical traces that must cross over one another to complete the layout design are minimized Additionally the PIC microcontroller has a flexible remappable peripheral structure 9 so rewiring of certain interfaces to improve routing on the board may be performed For the Gauntlet design the microcontroller is utilizing an 12MHz external crystal oscillator so space must be allocated around the oscillator to minimize noise related clocking errors The chosen 26 ECE 477 Final Report Spring 2010 microcontroller has three sets of power and ground connections as well as an additional decoupling capacitor connection pin analog ground and power pins and core voltage pin 9 All of these are decoupled using decoupling capacitors placed as close to the microcontroller as possible In spite of the fact that many of the microcontroller pins are being used there are no noteworthy diffi
56. o trigger occurs audio samples must be selected The first audio sample e g Your current velocity is or The slope grade is is determined by the audio output mode Numeric values are parsed into their constituent components For example the number 362 would be parsed into 300 60 2 which is further subdivided into four audio samples three hundred sixty and two Because of the nuances of the English language special cases are needed to avoid playing numbers like 31 ECE 477 Final Report Spring 2010 ten three when thirteen is meant Finally a unit of measure e g meters per second is output The chosen samples are found on the microSD card through a table lookup of filenames The available 512 byte audio buffers are filled to capacity and then the PIC enters a time critical segment of code which feeds blocks to the MP3 decoder and read new blocks from the microSD card stopping only when the samples are completed or the decoder indicates that it no longer has buffer space The SPI interface used by the microSD card and the VS101 le is clocked at a very fast MHz rate to avoid buffer underflow and by extension cracked and halting sound 11 0 Version 2 Changes We would make several changes to the Gauntlet in a second revision The first changes deal with schematic errors most notably the audio oscillator component and the charge counter circuitry A 12 288 MHz oscill
57. ocation to a set destination waypoint characterized by comprising destination waypoint setting means for setting a destination waypoint history storing means for storing positional information on destination waypoints and the latest dates when the stored destination waypoints were used for guidance therein storage controlling means in response to an instruction for guidance start to the set destination waypoint for checking the history storing means if the set destination waypoint is already stored in the history storing means if yes renewing the latest date S7 for the set destination waypoint in the history storing means and if not storing positional information on the set destination waypoint in the history storing means at a predetermined timing S9 displaying means for displaying the positional information stored in the history storing means and destination waypoint selection means for selecting a destination waypoint with referring to the displayed positional information Claim 4 A navigation device for providing guidance from a user s current location to a set destination waypoint characterized by comprising destination waypoint setting means for setting destination waypoints history storing means for storing positional information on the set destination waypoints therein storage controlling means for storing positional information on destination waypoints in the history storing means at a predetermined timing when destination
58. ocontroller in C Over the course of the semester my previous experience with PIC microcontrollers was very valuable to the success of the project I provided consultations on the design of the system including helping to select the PIC microcontroller after discovering that trigonometric functions could be implemented on the microcontroller using libraries provided by microchip A second very valuable contribution I provided to the team regarding the microcontroller was the suggestion to check the microcontroller silicon errata to ensure that the peripheral pin selections we made did not result in unforeseeable errors As it turned out there was a problem that rendered one of the three sets of programming pins on the microcontroller inoperable which we avoided while another team had to redesign due to this problem When it was discovered that the MP3 decoder chip did in fact require an oscillator it was my suggestion to clock the PIC off of a 12MHz external clock that could be shared with the decoder IC While this approach had to ultimately be abandoned the 12MHz crystal oscillators ordered were used for both the microcontroller and MP3 decoder IC Additionally due to previous hobby electronics projects I had previous PCB layout experience that I brought to the team Design and layout of the PCB was an area in which I had major responsibilities I explored the PADS PCB layout program figuring out the initial approach for making custom footprints
59. om for some plastic screw guides used to seal the casing 23 Additionally in order to mount the circuit board to the casing four mounting holes are required on the PCB 23 Due to the nature of the casing certain components that need to be accessible from the outside of the casing such as the power switch SD card power barrel jack and audio jack must be placed on the right side of the PCB where they can easily be machined to access the casing s exterior 9 3 PCB Layout Design Considerations Sensors Aside from these general considerations certain components such as the accelerometer needed to be positioned as close to PCB mounting points as possible ideally within 1 inch This is done to reduce the effects of PCB resonance on the sensor readings from the accelerometer 29 Also the Gauntlet system requires two separate grounds for analog and digital The junction for these grounds needed to be placed as close to the MP3 decoder chip as possible in order to provide latch up immunity 30 The MP3 decoder chip also requires a dedicated external 12MHz oscillator which cannot be shared with the microcontroller as the decoder chip grounds the clocking signal when in reset mode 30 Also several of the sensor systems such as the accelerometer and altimeter units were unavailable in packages that could be easily hand soldered so breakout boards were required for these systems As a result it was important to place these parts sufficie
60. om datasheets Batteries UnionBattery 2000mAh pdf Accessed Feb 18 2010 25 LTC4150 Coulomb Counter Battery Gas Gauge Linear Technology 2003 Online Available http cds linear com docs Datasheet 4150fc pdf Accessed Feb 18 2010 35 ECE 477 Final Report Spring 2010 26 POLSTAR PMB 648 GPS module Parallax Online Available http www parallax com Portals 0 Downloads docs prod sens PMB 648 Specification _VO 1 pdf Accessed Feb 18 2010 27 NHD C0220BiZ FSW FBW 3V3M COG Chip on Glass Liquid Crystal Display Module Newhaven Display International Nov 20 2009 Online Available http www newhavendisplay com specs NHD C0220BiZ FS W FBW 3V3M pdf Accessed April 3 2010 28 Kyocera Elco MicroSD Card Connector Online Available http www kyocera elco com prdct pdf 5138 pdf Accessed February 25 2010 29 Analog Devices ADXL345 Datasheet Online Available http www sparkfun com datasheets Sensors Accelerometer ADXL345 pdf Accessed February 24 2010 30 VLSI Solutions VS1011e MP3 Audio Decoder Datasheet Online Available http www vlsi fi datasheets vs1011 pdf Accessed February 24 2010 31 Air Pressure and Altitude Above Sea Level The Engineering Toolbox 2005 Online Available http www engineeringtoolbox com air altitude pressure d_462 html Accessed March 22 2010 32 NMEA Reference Manual
61. ost DC DC converter and the values of discrete components in the regulator circuit were calculated to provide a 3 3 V up to 600 mA power supply to the rest of the circuitry 15 Battery life is monitored by the LTC4150 Coulomb Counter Battery Gas Gauge The coulomb counter senses the current into or out of the battery using a sensing resistor Worst case current draw from the battery into the circuit is under 250 mA and charging current into the battery could be as much as 450 mA so 450 mA was used as the limiting current in calculations for the sense resistor 16 A 0 1 Q sensing resistor is used to limit voltage across the resistor to 50 mV The coulomb counter sends an interrupt to the microcontroller when a certain amount of charge has passed through the resistor in either direction allowing instantaneous battery capacity to be determined A polarity pin allows distinction between charging and discharging interrupts 25 The battery is charged by the MCP73811 Li Polymer Charge Management Controller It charges the battery at 450 mA and 4 2 V both of which are consistent with the requirements of the battery 16 24 It is attached to a power barrel jack to which an external power supply can be attached to recharge the battery 8 1 3 Flash Memory 22 ECE 477 Final Report Spring 2010 The Gauntlet uses a 2 GB microSD card for flash memory storage Audio data and GPS waypoints are stored on the microSD card and accessed by the microcontro
62. protect the delicate electronic components inside from any crashes or falls 7 1 Commercial Product Packaging During the search for commercial products that could be compared to the Gauntlet we found one competitor in the Garmin Foretrex Series and one product that is similar in terms of packaging and demographic the Flaik Snow Sports Armband Both are wearable devices designed for outdoor enthusiasts that relay information The Foretrex Series is designed for runners however and the Flaik has a very different usage from the Gauntlet being more of a tracking device so that lost skiers can be found easier 7 1 1 Product 1 The Garmin Foretrex Series The Garmin Foretrex Series is a series of wearable GPS devices for hikers skiers and kayakers It is designed to be worn on the wrists while the Gauntlet is designed to be worn on the forearm In terms of functionality it is very similar to the Gauntlet in that it uses a GPS to store waypoints and keep track of its user s position 20 The packaging of the Foretrex is very small It is designed to be worn like a wristwatch and thus has about the same weight as one The embedded system is strapped to the user s wrist using a Velcro band Much of the space is taken up by the monochrome LCD screen which displays a path from where the user had been The Gauntlet s LCD screen will only display characters due to most of the information being relayed through audio 18 ECE 477 Final Report
63. r Battery ADCMP361 Analog Comparator MCP73811T LiPo Charger LTC3440EMS Buck Boost Regulator Figure 1 2 System Block Diagram 2 0 Team Success Criteria and Fulfillment The Project Specific Success Criteria for the Gauntlet are as follows 1 An ability to communicate sensor data via audio to the user 2 An ability to recharge and monitor an on board battery 3 An ability to determine current location via GPS ECE 477 Final Report Spring 2010 4 An ability to direct the user to a safe waypoint 5 An ability to save acquired data to persistent storage Each of these five PSSCs was satisfied The Gauntlet communicates airtime altitude temperature and current velocity over a pair of standard headphones A lithium polymer battery is charged protected and monitored by several onboard components and the Gauntlet can relay the current battery status to the user using the character LCD A Polstar PMB 648 GPS receiver provides the user s current longitude and latitude and the Gauntlet is able to use this information to provide a compass arrow pointing back along the path to the initial safepoint during navigation Finally battery waypoint and preference information are saved to an onboard microSD card during operation 3 0 Constraint Analysis and Component Selection 3 1 Design Constraint Analysis Because the Gauntlet is a wearable device form factor is important Very few la
64. raps I also worked on the CAD of the first product model I created a model of the Ergo Case ECE 477 Final Report Spring 2010 in AutoCAD using a CAD sheet that I had requested from OKW Enclosures Inc and added the main user interface to the case as well as the Power Jack and Headphone Jack The CAD model that I had created was eventually used as our main model for the final product and the result was very close to what I had envisioned in the early weeks When the PCB came in after Spring Break I began to focus on my main specialty software Jacob and I worked together to create a basic skeleton of what we wanted the Gauntlet to actually do in software We also worked together on the GPS navigation algorithms After deciding that we would need some of our own fixed point notation variable types I helped come up with exactly how we would implement that and wrote the parser that we would use for translating NMEA sentences from the GPS into information that we would eventually use for the final calculations I also found Microchip s FAT 16 library so that we could easily interface with the SD card when the time came to use it My netbook also became our main interface with the SD card since I had most of the drivers installed to read it already and I added the mp3 files of my voice to the SD card that we used to talk to the user Toward the end of the semester I helped Jacob write the Menu System user interface I also did a lot of debugging
65. rate of 64 kbps This implies that reading samples from the microSD card and streaming them to the decoder is a critical microcontroller task 10 2 External Interface Mapping The PIC24F uses a remappable pin design allowing on chip peripherals to choose from a good number of I O pins Appendix G shows a full table of pin mappings to the external peripherals It should be noted that these pin mappings were chosen for ease of circuit board routing and not for their internal port name consistency or numerical order 10 3 Integrated Peripherals In order to communicate with the off chip sensors the PIC needs to utilize three SPI interfaces one UART interface and one I2C interface In addition an onboard ADC in single sample mode will be utilized to measure the battery voltage and the timer subsystem will be needed to perform periodic tasks Initialization of these peripherals is done though memory mapped registers which are described in Appendix I 10 4 Application Code Organization The Gauntlet being a battery powered device is primarily interrupt driven When a timer SPI UART or other interrupt is fired the interrupt handler sets appropriate flags and wakes the microcontroller The main loop reads these flags and takes the required action going back to sleep only when a full loop is executed without any interrupt activity A fuller description of the actions the main loop may take is described in Section 10 6 10 5 Debugging Provisions
66. rge components could be chosen those components that are larger modules need to be low weight so that the device is comfortable to wear The entire printed circuit board must be small enough to fit easily on an arm and the components chosen needed to be durable enough to survive falls by the user Because the device is battery powered most components need to have low power consumption Finally because the device is designed to be worn while skiing or snowboarding it is very important that each component can operate at temperatures below freezing Our team has been very careful to select components that are operational to a minimum of 20 C 3 1 1 Computation Requirements The Gauntlet receives GPS data including current position horizontal velocity and a rough estimate of altitude once every second Combined with the more precise altimeter data from the pressure sensor the microcontroller needs to calculate downhill velocity for presentation to the user which requires trigonometric functionality The onboard accelerometer must be periodically polled for jump and crash conditions and the pressure sensor provides on demand temperature and altitude information In emergency mode the microcontroller needs to navigate the user though a series of GPS waypoints which again requires trigonometric computation Finally audio samples need to be buffered into memory from a microSD card and streamed to the audio controller during an audio output ro
67. rometer to share Because the sensor data is not time critical the altimeter and accelerometer can be multiplexed This will require two GPIO pins for use as chip selects An I2C bus is required for the low power LCD and the GPS unit requires a UART for serial communication In total our peripherals require a minimum of one I2C bus three SPI interfaces and one UART on our microcontroller 3 1 4 Off Chip Peripheral Requirements The off chip sensor requirements for the Gauntlet are as follows one GPS receiver module one absolute pressure sensor and thermometer a three axis accelerometer and a Coulomb counter for the lithium polymer battery The user interface requires three pushbuttons an MP3 decoder and an I2C LCD which are described in detail below Finally a microSD card is used for storing read only audio and user defined GPS altitude waypoints No other glue logic or off chip peripherals are needed ECE 477 Final Report Spring 2010 3 1 5 Power Constraints Our armband is powered by an onboard rechargeable battery pack Because of this low power peripherals are paramount to usability The Gauntlet has a target battery life of ten hours so most of our off chip peripherals need to either have a low power mode or have the ability to be turned off by the microcontroller when not needed Also our power regulation circuit will need to be highly efficient This implies that very few of our chips will be dissipating a lot of power but
68. s translation is greater than a given threshold a new waypoint is saved to persistent microSD storage Depending on the time available to the PIC an optimization routine may be implemented to search through the stack of waypoints determine if the most recently added waypoint is within the threshold of a previously added waypoint and reset the stack to that point to avoid directing the user in loops The reaction to battery information is primarily bookkeeping If the analog reading and charge count have changed significantly they are backed up to Flash If the battery is dangerously low the user is notified and nonessential circuitry is shut down Since the Gauntlet can be charged while it is off and therefore not receiving charge count information the PIC will reset the charge count if the analog battery voltage is measured to be 4 20 volts Finally and possibly most trivially the PIC must react to user pushbutton input This comes mainly in the form of changing the operating mode updating the user menu and writing new data to the LCD 10 6 5 Output Output to the user comes in two forms the LCD display and the audio interface The LCD display is trivial as the interface to the LCD is a simple I2C system The audio interface will therefore be the topic of discussion here The trigger for audio output is a user configured timer The mode of audio output e g velocity airtime or slope grade is also determined by the user Once the audi
69. se the Flaik does not have the human interface needs of the Gauntlet its packaging can afford to be much smaller 19 ECE 477 Final Report Spring 2010 Figure 7 2 The Flaik Snow Sports Armband 7 2 Project Packaging Specifications The packaging used for the Gauntlet is the OKW Ergo Case plastic enclosure 22 The case itself is designed to be worn on the forearm as shown in Figure 7 3 Because the material is plastic it fits the lightweight but sturdy criterion that is needed for the Gauntlet to perform its functions without hindering the user The ergonomic design of the enclosure ensures that the user can wear it on their arm without any discomfort and there is plenty of room inside the case for the components that were selected previously The character LCD screen was placed at the approximate center of the top of the case so that the user can see it without much trouble and for the more aesthetically pleasing symmetric placement The pushbuttons for the user to interact with are below it The audio jack is on the side of the case toward the user see back view in Appendix B Some holes were to be drilled onto the case for the above specifications to be put in as the case does not come with them The cost of the enclosure is 22 32 per unit the eyelet kit is 3 04 and the belt strap is 4 92 making the total cost of the packaging 30 28 However all of these are available as free samples from OKW Enclosures Inc
70. sign award The Australian Jun 3 2008 Online Available http www theaustralian com au news flaik skis its way to a design award story 0 1111116516898 Accessed Feb 1 2010 2 SCP1000 Series 120 kPa Absolute Pressure Sensor VTI Technologies Online Available http www sparkfun com datasheets Components SCP 1000 D01 pdf Accessed Jan 31 2010 3 MP3H6115A Series Datasheet Freescale Semiconductor 2009 Online Available http www freescale com files sensors doc data_sheet MP3H6115A pdf Accessed Jan 31 2010 4 BMA150 Data Sheet Bosch Sensortec May 30 2008 Online Available http www bosch sensortec com content language1 downloads BMA150_DataSheet_Rev 1 5_30May2008 pd f Accessed Jan 31 2010 5 ADXL345 Analog Devices Jun 2009 Online Available http www analog com static imported files data_sheets ADXL345 pdf Accessed Jan 31 2010 6 VS101le MP3 Audio Decoder VLSI Solutions Oct 6 2009 Online Available http www vlsi fi fileadmin datasheets vlsi vs1011 pdf Accessed Jan 31 2010 7 STA013 MPEG 2 5 Layer III Audio Decoder STMicroelectronics Feb 2004 Online Available http www st com stonline books pdf docs 6399 pdf Accessed Feb 1 2010 8 GPS Comparison Table Parallax Inc 2010 Online Available http www parallax com ProductInfo Accessories GPSComparisonTable tabid 83
71. since the Gauntlet is small package strapped to the arm of the user it is important to keep the operating temperature down 3 1 6 Packaging Constraints The Gauntlet is unobtrusive enough to wear on the arm This means that it is small enough not to interfere with a skier snowboarder s arm movements while on the slope The device needs to be no more than a few centimeters thick and be no longer or wider than a below average upper arm Also it weighs five ounces or less to ensure that it can be comfortably strapped to the user The Gauntlet needs to be durable enough to survive a hard fall onto packed snow or ice without injuring the user or becoming damaged 3 1 7 Cost Constraints The closest competitor to the Gauntlet appears to be the Flaik snowsports armband described in detail in 1 Unfortunately there appears to be no readily available pricing information for the Flaik it needs a resort wide network to work so Flaik systems are not sold to the general public It seems likely that an armband such as the Flaik would run at least 200 300 if sold individually Similarly GPS enabled armbands and wristwatches for runners tend to cost approximately 300 The Gauntlet needs to be priced in this range to be competitive 3 2 Component Selection Rationale 3 2 1 Altimeter The two pressure sensors which were considered for use on the microcontroller were VTT s SCP1000 D01 2 and Freescale s MPXA6115 3 The SCP1000 is an extremely low
72. stop bit Status and Control 00 transmission interrupt when buffer has UTXISEL lt 1 0 gt space UTXINV 0 TX idle state is 1 UTXBRK 0 sync break disabled UTXEN 1 transmit enabled URXISEL lt 1 0 gt 00 interrupt when single character received Baud Rate Generator BRG lt 15 0 gt 0x0019 9600 baud 0 16 error Status Register SPIEN 1 enabled SPISIDL 0 disable in IDLE mode Control Register 1 DISSCK 0 internal clock enabled DISSDO 0 SDOx pin enabled MODE 16 1 Communication is 16 bits wide SMP 1 input sampled at end of clock CKE 0 negative clock edge for output SSEN 0 slave select not used CKP 1 high idle clock MSTEN 1 master SPRE lt 2 0 gt prescaler different for different modules PPRE lt 2 0 gt prescaler different for different modules Control Register 2 FRMEN O framing disabled SPIFSD 0 frame sync disabled SPIBEN 0 enhanced buffer mode disabled Control Register I2CEN 1 enabled I2CSIDL 1 disable in IDLE mode A10M 0 7 bit addressing DISSLW 1 slew rate control disabled SMEN 0 disable SMBus thresholds ACKDT 0 negative ACK Baud Rate Generator BRG lt 15 0 gt 0x0012 400 kHz
73. such as Garmin car navigation systems but due to the prevalence of prior art with GPS technology and GPS being contained in the public domain patent liability is not expected to present serious problems for the Gauntlet project 4 1 Results of Patent and Product Search 4 1 1 Route Based on Distance 11 Patent No 7 627 423 Filed March 10 2005 Condensed Abstract ECE 477 Final Report Spring 2010 The patent describes systems methods and a device for generating a route based on distance An example provided by the patent is software instructions to receive a distance input and generate a route based on the distance input Key Claims Claim 1 A portable electronic device for generating a running route comprising a global positioning system GPS receiver a processor a memory in communication with the processor and program instructions storable in memory and executable by the processor to receive a distance input and to generate a running route that begins at a starting location and ends at the starting location and to receive location information from the GPS receiver to track the portable electronic device along the running route wherein the running route has a length substantially equal to the distance input and wherein the running route includes an off road portion Claim 9 A portable electronic system for generating a running route comprising a first computing device connectable to a network wherein the first co
74. to port this to our project to reduce development effort This library provides stdio type file operations which are well worth the time and memory overhead to the Gauntlet 10 6 3 Calculation Processing The calculation module encompasses the algorithms which combine sensor data to provide new information This includes the calculation of the downhill velocity the slope grade the distance and direction to the last saved waypoint and the distance and direction to the user saved safepoint Calculation of the velocity is fairly straightforward The GPS chipset can provide a birds eye velocity reading or XY velocity once every second The change in altitude over the previous second or Z velocity can then be combined with the XY velocity using the familiar Pythagorean theorem Slope grade is calculated with the same input but this time the quantity is the ratio of the Z velocity to the XY velocity Waypoint distance and direction calculation is significantly more involved The microcontroller will start with the latitude and longitude in degrees and the altitude in meters of both waypoints The approximate distance between two points lat1 long1 and lat2 long2 with a radius of the earth r is equal to r acos sin lat1 sin lat2 cos lat1 cos lat2 cos long1 long2 34 An accurate calculation then will require six trigonometric calculations eight floating point multiplications four of these are to convert to degrees an
75. ttp ww1 microchip com downloads en DeviceDoc 22036b pdf Accessed Feb 18 2010 17 RoHS Guide com RoHS Compliance FAQ RoHS Guide FAQ on RoHS compliance 2010 Online Available http www rohsguide com rohs fag htm Accessed Apr 15 2010 18 Hoag Hannah The missing greenhouse gas Nature Reports Climate Change July 10 2008 Online Available http www nature com climate 2008 0808 full climate 2008 72 html Accessed Apr 15 2010 19 Buchmann Isidor Recycling batteries Battery University com July 2003 Online Available http www batteryuniversity com partone 20 htm Accessed Apr 16 2010 20 Garmin Ltd Foretrex 301 Online Available https buy garmin com shop shop do cID 144 amp pID 30025 Accessed February 8 2010 21 S Fallon The Flaik Armband Tracks Your Airtime on the Ski Slopes Online Available http gizmodo com 5012805 the flaik armband tracks your airtime on the ski slopes Accessed February 9 2010 22 OKW Enclosures Inc OKW Ergo Case Enclosures Online Available http www okw co uk products okw ergo htm Accessed February 9 2010 23 OKW Enclosures Inc ERGO CASE M Online Available http www2 okw com okw static drawings pdf 00006701 pdf Accessed February 10 2010 24 585460 Li Polymer Battery Packs Specification UnionFortune Mar 16 2006 Online Available http www sparkfun c
76. utine ECE 477 Final Report Spring 2010 Of these requirements only the streaming audio is time critical This requires a minimum throughput to present acceptable audio quality All other computations can be done on demand from the user so small delays will be acceptable 3 1 2 Interface Requirements The Coulomb counter used for battery life monitoring requires three pins to function one for a periodic count pulse one for the count polarity charging vs discharging and one for a digital reset Three pushbuttons interface to the microcontroller to allow the user to select an operating mode for the Gauntlet Because the microcontroller has a limited number of onboard SPI peripherals two GPIO chip selects are required to multiplex the accelerometer and altimeter thermometer ICs Two pins are required to use the accelerometer s free fall and motion interrupt support and two pins are required to signal an altitude measurement and receive a measurement interrupt from the onboard altimeter One pin is needed to shut down the LCD for low power consumption Finally one pin is needed to shut down the audio decoder when its capabilities are not needed by the system In total the microcontroller requires fourteen GPIO pins for its interfaces 3 1 3 On Chip Peripheral Requirements The Gauntlet s off chip peripherals require a minimum of three SPI interfaces one each for the audio decoder and microSD card and one for the altimeter and accele

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