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mbed:cycling_computer [2008/11/22 16:28] (current)
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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!
mbed/cycling_computer.txt · Last modified: 2008/11/22 16:28 (external edit)