RobMeerman.co.uk

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====== Cycling Computer ======

I intend to make a ludicrous bicycle computer, which will do silly things like:
  * Measure speed using the optical sensor from an old mouse
  * Measure the berth overtakings cars give with ultrasound
  * Measure acceleration using an accelerometer
  * Log GPS coordinates
  * Run a GUI on a Nintendo Game Boy Advance (although I may do this bespoke as well...)

===== Data =====
  * [[mbed:cycling_computer:Bike Measurements]]
  * [[mbed:cycling_computer:Journal]]

===== To Do =====
==== Physical ====
  - Photograph bike for purposes of overlay-sketching and progress measurement
  - Find packaging for the eletronics
  - Decide how to mount sensors / microprocessor onto bike frame
  - Create mount-points and place wires (unless wireless is decided upon)

==== Electronics ====
  * Wheel RPM
    - Decide whether to use a reed-switch & magnet, wire-loop & magnet or LDR & LED/Blinkers
  * Pedal RPM
    - As for wheel RPM
  * Airspeed
    - Buy pressure sensors and calibrate a (remember what the hell it was called - it's in the Windows Journal files, reboot into Windows, export it all and never look back).
  * Acceleration
    - Get an accelerometer
  * Location
    - GPS reciever

==== Software ====
  - Investigate software timers which fire interrupts. Simon said something about these, and I'd not heard of them. They seem a lot simpler than a PWM loopback. Though not nearly as hacky ;-)
  - Reference Clock (see below) needs a pull-up (or pull-down) resistor. Just shorting PWM-out to INT-in won't work.
  - Use PWM2 to verify accurate rate detection using new reference clock
  - Display rate in rpm and kmph.

===== Roadmap =====

  - Use optical mouse sensor to read speed (and wobble?)
    - Probably simplest to avoid using USB mouse, [[http://www.computer-engineering.org/ps2protocol/|try PS2 instead]].

===== Physical Bike Properties =====

Rear wheel circumference at 60psi: 2m 4cm (readings were 2m14, 2m04, 2m06, 2m04.5)



===== Maths =====
Assuming that the wheel of my bike as a circumference of 1m, and that I reckon the practical upper limit for my bike is 50mph (~80kmph)((I don't expect to be able to //cycle// at this speed, this is just the upper limit I've chosen to design my system for)) then I can expect my bike wheel to do about 20 rotations per second. In order to sample this effectively, I should be sampling at 40Hz.

However, I won't have an analog measurement from the wheel. I will have a pulse once per rotation. I can configure the board to fire an interrupt on this pulse (by catching the rising edge, for instance). I can also connect one of the PWM modules to an interrupt and use it to generate my reference clock.

So I can have a ''tick()'' interrupt fired at 40Hz, providing an accurate reference signal, and another interrupt fired for each rotation of the wheel. By counting ticks between wheel rotations I ought to be able to work out my speed fairly accurately.

===== 88 subs per second =====
A "sub"((As in sub-way sandwich)) is approx. 6 inches. 30mph = 44 feet/s = 88 subs/s: Great Scot!
RobMeerman.co.uk

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