Getting Started with Arduino

Python script to launch the UI, monitor the serial/USB port with the Arduino and to update the UI. The source of the template code I modified is in the comments

The UI (python/Qt4 on Linux, Fedora 16). Simple so far but effective

Here's the circuit as scheched using Scheme-it. 

Scheme-it was easy to get this far with - only took a couple of minutes. Didn't need to log-in.

L1 is toggled on/off by Pin 12 as the reed switch gets activated and grounds Pin 2.

Adafruit is a good place to get basic Arduino tutorials. The basic interrupt code example I buit from came from the main arduino site.

Code for the Arduino - double click to select and copy...

Power

One goal of this project was to have the computer display power. Since my old Cyclops trainer is not adjustable, power should be a function of speed. Fortunately power curves for some Cyclops trainers are published : http://www.cycleops.cz/files/trainers.pdf. I decided to use the Fluid2 curve - my trainer's older than that but hopefully close enough. A curve-fit using Excel gave :
Power[W] = 0.0128V3 - 0.0163V2 + 8.2864V where V is speed in [mph]

The Computer End

Here's the Arduino interface. Black and yellow wires at left come from the reed switch on the bike. Pin 2 senses the reed switch (yellow wire). The 100ohm resistor is to protect the Arduino in case pin 2 gets configures as an output by mistake. A 10k pullup resistor connects to the 5v pin (red wire). Then LED is activated by pin 12 (green wire)  - it is programed to change stage as the magnet passes the reed switch and is helpful for quickly checking the system works.