For the transmitter a simple oscillator is pretty easy to build. The
biggest problem would be frequency stability unless you use a crystal or
resonator - in which case you would probably have to stick to some form of
AM. Checkout "bug" designs on the web.

I guess that what yo uneed as a transmitter is largely going to be
determined by what you use as a receiver. - How about buying/locating an
old "Radio Controlled" toy of some sort.  Cheap ones are available new (in
NZ) for $20 or less but damaged/ broken or faulty ones are just chucked
out. May be an option.This will give you both a simple transmitter &
receiver and you only have to figure out the modulation & detection issues.

 I like the idea of directly modulating the osc. by the rotating inductor
though.

Alternatively, you could build your own superregen receiver but they can be
a bit tricky to get good performance out of.

If you have trouble finding circuits let me know but it should be easy to
find something via google.

Richard P





Hi all,

Was away from email for the past two days and could not respond,

First thanks for all your suggestions. I guess I should have provided some
more information, this is a personal project and I was hoping to venture
into new territory as a learning experience :-).

basically I am trying to develop a rollerblade speedometer. There are
commercial ones available
http://www.skates.com/Skate_Speedometer_p/mcrsprt8082.htm but I figured it
would be interesting to build one that would combine the speedometer with
Heart rate measurements etc. Anyways you can see why wireless would be the
best option here (IMHO), with an optical solution not only do you have
alignment issues but you also need to worry about what happens when the
user rollerblades through a pool of muddy water and the led get's splashed
etc.

Richard Prosser & Robert B- Like you suggested a simple RF Osc might be the
best option. Any circuits that you might like to share?

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)

Phil & Olin - I see where you are coming from I could just add another
micro at the wheel and transmit info ( I need a micro at the recieve end
also to keep track of dist travelled, average mph etc)  but I was hoping
for a minimalist solution, although I realize that the time I spend getting
it to work would probably cost me more.

Thanks again for all your suggestions, I guess it's time to start
experimenting!






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