I think most bicycle computers use a magnet moving past a reed switch to detect revolutions. Is this right, or do some use the magnetic pulse (zero cross?). To get to the point: How might I supply a an alternative signal to the cycling computer's input that it will recognize?

If I can get that to work, it'd be a very inexpensive data acquisition logging device that is also small and portable.

 

I've got 2 cheap cycle computers and they both use reed switches - you can hear them if you put a magnet near them.
A mosfet could replace the switch and maybe work.

 

I've got 2 cheap cycle computers and they both use reed switches - you can hear them if you put a magnet near them.
A mosfet could replace the switch and maybe work.

Maybe. There must be some polarity to the two contacts, and a tiny current flowing when the reed switch closes. Supplying a square wave thru a high ohms resistor might fool it, if I can figure out which side is "ground". I'll see if I can read anything on the DVM.

 

An opto-isolator might do it too. Would it be an advantage to separate the computer and driver electronics?

 

An opto-isolator might do it too. Would it be an advantage to separate the computer and driver electronics?

Separation would alleviate my main concern about experimenting - inadvertently zapping my cycling computer. I believe I've got an old opto-isolator in my parts drawer, so I'll take a look at the datasheet.