andrew12345678 said:I have ordered 3 16F88 so i will be definately using a PIC.
I guess i'll have to test the magnets and if they arent strong enough i can mount them closer. Good thing you reminded me about the inverse square law, i'll need that for end of year exams
Microchip is actually very good at handing out free samples of their chips. You'll need a non-yahoo/hotmail/etc. email account, though:
http://sample.microchip.com/Default.aspx?testCookies=true
Also, I've found that reed switches work well (perhaps even better), and they in general cost less than an Hall effect sensors.
As for LED brightness, I would get the brightest you can find. Then you can run them at lower currents to save on battery power.
Figure out a way to mount the batteries as close to the wheel center as possible. I rode 40 mi. with a bicycle pov on my back wheel, and I definitely had to work harder to pedal it. I also didn't distribute the batteries evenly around the wheel, so there was an imbalance which was very noticeable at higher speeds.
Finally, consider using AAA's instead of AA's. They are 1/2 the weight but still have 1200 mAH which probably will be enough to power you through the entire race - it all depends on your LEDs.