Magnetic something ? ? ?

Maybe not a best idea for a topic but what is called the chip or component they use on bicycles or to measure the speed of a motor thru a magnetic field. I remember how it works and what is it for but I don't remember the actual name. (magnetic sensor)

Comes in a transistor form way with 3 pins or like a zener diode tube or the chip style with 3~4pins.

Can you please provide me with some names.

Thanks

D.60

Hall effect or reed relay

Yep, thanks a lot, that's what I was looking for.

Domino60: Yep, thanks a lot, that's what I was looking for.

Which one Hall or Reed? I'm gonna guess reed, due to your physical appearance comparison to a zener diode. Reed switches are often small glass tubes.

I've a general question - why glass and not plastic? I have broken several reed switches while making on/off switches for 'altoids box' circuits. They are soo delicate!

I've a general question - why glass and not plastic?

My opinion about hall and reed.

Reed switches in a glass tube are good for big magnetic fields/magnets cause they come in different dimensions and different magnetic fields (stronger..etc) and they are easy to be protected in a thin layer of hot glue or heat shrink tube or both not making a mess.

Hall magnetic chip's serve more purposes and they are sensitive to magnetic fields like a coil from a motor or transformer, it's really good for sensitive measures like cables in the wall ..etc

For example for a bicycle to measure the speed I would of chose hall cause they are more sensitive and can measure faster the change of a magnetic fiend while the wheel spins really fast, in the other way the reed tube switch if there is no a strong enough magnetic field it will not activate in every spin of the wheel and give you wrong data/speed.

So it depends what kind of project you got.

D.60