1. 1 Wireless Ski Timing System MDR Presentation Professor A. Muschinski Mike Coughlin Philip Da Silva Dave Pomeroy Nick Hnatiw SDP 2005

2. 2 Presentation Outline Dave:Review of Project, MDR Specs/Accomplishments Mike: Clocks, Interrupts, Delays Phil: Project Versions, C Code Nick: Wireless Communication, Budget, Conclusion

3. 3 Wearable clock keeps racer’s time while racer is on course Finish stops wearable clock, which transmits race time to finish unit. Here times are recorded for scoring 3 Part System: Start, Wearable Timer, Finish Start Racer starts by tripping start wand Finish Racer finishes by tripping IR beam Timer Strapped to racer Controlled by start and finish units Timer in wearable clock starts when racer trips the start wand

4. 4 MDR Specifications GoalAccomplished? Clock unit keeping time using interruptsYES 10 ms accuracy for the entirety of a raceYES Wireless communicationYES Clock unit Keeps time through a start and a stop interrupt Accurate to the hundredth of a second Will not wander more than 10 ms over five minutes Wireless Communication Communicate through two transceivers Transceiver chips controlled by two PICs

5. 5 Accomplishments Clock Unit Accuracy: 10 ms over 22 minutes (based on clock error ppm) Precision: 61 µs (based on clock speed and implementation) Wireless Communication Two transceivers communicating data

6. 6 Presentation Outline

7. 7 TCXO Rated for use in temperature range -40C to +85C ±7.5ppm => ± 4min/yr => Max race time of 22min Responsible for keeping accurate race time

8. 8 Two Interrupts

9. 9 Clock and Instruction Cycles 4MHz system clock allows for fast interrupt service PIC16F877 instructions: 4 clock cycles = 1 instruction cycle = 1 µs 2 instruction cycles for branch instructions 1 instruction cycles for all other instructions

10. 10 Delay Times Examination of compiled assembly code Worst Cases 33µs worst case result difference 40µs worst case overall delay

11. 11 Presentation Outline

12. 12 C Code V00 – VFD functionality V01 – Moved VFD, input pin for buzzer V02 – Timer0 interrupt, 1s beep V03 – Classified V04 – Timer0 uses TCXO, external interrupt, time calculations and conversions V05 – Rewrote timing conversion

13. 13 Timer_Module.c Priority based – 1 st Timer0, 2 nd External Additional Time Calculations get_timer0( ) on each gate trip Convert returned integer to fraction of Timer0 interrupt time Subtract start gate time, add finish gate time from total time

14. 14 Convert_time.c Mother variable ‘cnt’ scaled by time constant Conversion formula ‘cnt’ to hours, minutes, seconds, and hundredths Overflow problems! 17 minute overflow still within 5 minute spec To be fixed regardless

15. 15 Presentation Outline

16. 16 Wireless Communication Micrel RFB915 Module Operating range: -20°C to 75°C VCO (voltage controlled oscillator) Frequency Modulation Frequency 902 – 928 MHz Programmable frequency dividers Data rate of 9200 bits/sec

17. 17 Wireless Communication 3 Registers set the frequency N,M, and A registers hold the frequency values Registers are 12, 10, and 6 bits respectively Values are determined using following equation: f xco / M = f RF / (64*N + A) 80bit control word entered at power-up Sets internal values

18. 18 Budget Total amount spent$186.42 Planned future purchases~$200 Remaining budget for CDR ~ $100

19. 19 Conclusion MDR specifications met Accurate timing Wireless communication Future milestones Three units with wireless transmission of data Menu system for the finish unit with user input Timing within specification Field tested units

20. 20 This is the end

21. 21

22. 22 Relativity Concern? t is the time interval in the stationary frame t1 is the time interval in the uniform motion frame v is the relative speed c is the speed of light, t = 300 seconds (longest ski race ever) v = 200 mph ~ 90 m/s (fastest skier ever) c = 300000000 m/s Result: No detectable difference between stationary frame and motion frame.