Hello all,
Newbie here. I have one of those little electronic speedometers for bicycles. There is a little magnetically activated sensor at the end of a pair of leads. I need to know what electronic part is in the end of this sensor. Mine is broken, and if I new what this little piece was I could repair it.

It was encased in glass or plastic. And had a thin strip of metal attached to each of the leads entering from either end.

TIA
Neil

 

More info would be helpful. but I'm guessing that the part you seek is called a "Reed Switch" available at most electronics outlets. The principle is simple, when the magnet approaches the switch it is closed, then counted by Your circuit.

 

That sounds exactly like what the device does. I'll look around to see if one is available.

Thank you
Neil

 

I've owned several of those and I'd guess that there's a coil inside that delivers a small voltage to the computer each time the magnet passes. As posted already, it could also be a reed switch however my experience is that the magnet need not be all that close to generate the pulse. One thing you might do is test the resistance with an ohm meter. That presumes you have a known good device. Alternatively you could apply the ohm meter then bring a magnet up against it to see if anything changes.

My recollection is that the wire is very much like headphone wiring - very flexible but very fine and a challenge in terms of making connections.

If I can find one at home tonight I'll check the sensor with a meter to see what I get.

__________________
stevez

 

Any speedo's I've seen/owned have been reed switches.
It would be clever to use a coil... but that's just seemingly not done. :?:

 

I found a smallish reed switch, looks and is described exactly like the one I had. So I ordered three. The innards are not of a coil type. It is a little amppule type thing with two very thin strips of metal.

Peace
Neil

 

If you cannot find something suitable as a replacement, you might consider going to a home alarm shop. Most of the window/door perimeter switches are nothing more than the reed switches you described, and they come in a variety of packages and sizes. One in particular is about the size of a pencil, encased in plastic, and made to mount end to end with the magnet which is drilled and pushed into a hole in the adjacent door surface to the reed switch. Keep in mind there are two types of switches sold, normally open and normally closed.
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