On Thu, 9 Dec 2004, Jay Shroff wrote:
> Anyways, I was toyin around with maybe a simple CW type transmitter 
> (maybe just a 1 trans oscillator) triggered by a hall sensor, but I like 
> Peter Peres idea about capacitive modulation. This would really simplify 
> the sesor and then all the computing can be done at the wrist. (Can 
> anything say geek better that a 3"  computer on your wrist)

The capacitive oscillator modulation only works well when it is otherwise 
stable. I don't think that a roller blade is a stable device in this 
context. However I happen to know that many rollerblades use translucent 
plastic tyres which also cover the ball cages. So you can send a laser 
beam through the ball cage at that level and count passing balls with a 
phototransistor on the other side of the wheel. That signal could be used 
to key a 433 MHz transmitter directly. Keep in mind that the ball cage has 
half the rpm of the wheel.

good luck,
Peter
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