1

Wireless Ski Timing SystemMDR Presentation

Professor A. MuschinskiMike CoughlinPhilip Da SilvaDave Pomeroy

Nick Hnatiw

SDP 2005

2

Presentation Outline

Dave: Review of Project, MDR Specs/Accomplishments

Mike: Clocks, Interrupts, Delays

Phil: Project Versions, C Code

Nick: Wireless Communication, Budget, Conclusion

3Wearable 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 wandFinish

Racer finishes by tripping IR beamTimerStrapped to racerControlled by start and finish units

Timer in wearable clock starts when racer trips the start wand

4

MDR Specifications

Goal Accomplished?

Clock unit keeping time using interrupts YES

10 ms accuracy for the entirety of a race YES

Wireless communication YES

Clock unit Keeps time through a start and a stop interrupt  Accurate to the hundredth of a secondWill not wander more than 10 ms over five minutes   

Wireless CommunicationCommunicate through two transceiversTransceiver chips controlled by two PICs 

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

Presentation Outline

Dave:Dave: Review of Project, MDR Specs/AccomplishmentsReview of Project, MDR Specs/Accomplishments

Mike: Clocks, Interrupts, Delays

Phil: Project Versions, C Code

Nick: Wireless Communication, Budget, Conclusion

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

Two Interrupts

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

Delay Times

Examination of compiled assembly code

Worst Cases33µs worst case result difference

40µs worst case overall delay

11

Presentation Outline

Dave:Dave: Review of Project, MDR Specs/AccomplishmentsReview of Project, MDR Specs/Accomplishments

Mike: Mike: Clocks, Interrupts, DelaysClocks, Interrupts, Delays

Phil: Project Versions, C Code

Nick: Wireless Communication, Budget, Conclusion

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

Timer_Module.c

Priority based – 1st Timer0, 2nd External

Additional Time Calculationsget_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

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

Presentation Outline

Dave:Dave: Review of Project, MDR Specs/AccomplishmentsReview of Project, MDR Specs/Accomplishments

Mike: Mike: Clocks, Interrupts, DelaysClocks, Interrupts, Delays

Phil: Phil: Project Versions, C CodeProject Versions, C Code

Nick: Wireless Communication, Budget, Conclusion

16

Wireless Communication

Micrel RFB915 ModuleOperating range: -20°C to 75°CVCO (voltage controlled oscillator)Frequency ModulationFrequency 902 – 928 MHzProgrammable frequency dividersData rate of 9200 bits/sec

17

Wireless Communication

3 Registers set the frequencyN,M, and A registers hold the frequency values

Registers are 12, 10, and 6 bits respectively

Values are determined using following equation:

fxco / M = fRF / (64*N + A)

80bit control word entered at power-up

Sets internal values

18

Budget

Total amount spent $186.42

Planned future purchases ~$200

Remaining budget for CDR ~$100

19

Conclusion

MDR specifications met Accurate timing

Wireless communication

Future milestonesThree units with wireless transmission of data

Menu system for the finish unit with user input

Timing within specification

Field tested units

20

This is the end

21

22

Relativity Concern?

30090

30022

c

c

1

22

tc

vct

t is the time interval in the stationary framet1 is the time interval in the uniform motion framev is the relative speedc 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.