I unscrewed a few screws in my recumbent exerbike today to see how the electonics work.

On mine, these two little wires snake out of the guts and connect to a palm-sized box.

Inside the two little wires terminate in a piece of plastic the size of a large motherboard jumper.

And on the wheel is a magnet.

So is that little piece of plastic a reed switch? See I'm thinking of hacking my exerbike to a PC ...

-MF

Hmm, It could be used to count how many revs per minute your doing on the bike, It could also Be a Hall Sensor, Which Outputs a voltage Based on a magnetic Field. A Hall sensor (IMHO) is more interesting than a simple reed switch, since you can Do other stuff with them.

Thats actually how digital compasses work, they sense the earths magnetic field and output a voltage accordingly. There are actually 2 sensors for a digital compass, which ever has a greater magnetic field is north.

ADD: A Hall Sensor is a Linear Device, Ie, it follows y=mx+b format. X would be How many Gauss your magnet is (or How strong it is), While Y is your output voltage. Bring the magnet closer to the sensor, and you get more voltage, Further away, and you get less.

Wait, Its a 2 Pin Device?

Yeah two wires - I'm gonna unscrew the speedodometer and see where the other end of the wires go - I'm assuming a low-end processor with just enough smarts to drive the big LCD that shows MPH and elapsed time and all.

-MF

Pics are worth a thousand words

I'd love to post a pic or two, but the cover I took off is trapped in place by the pedal crank. I had a hard enough time just pointing inside to show SheWhoMustBeObeyed where the wires ended.
-MF