Tell me more ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote 11 down vote favorite
1

Most piezos I've seen have just two connections, but this type has three.
3-wire piezo
What's the third wire for?

share|improve this question
I accepted stevenvh's answer because it makes it clear to me. Don't let this stop you from posting other answers, however, possibly giving more detail. I might change my mind :-) – Federico Russo Aug 14 '11 at 14:10
It's a good answer. Nice and clear and to the point. – Russell McMahon Aug 15 '11 at 8:03

1 Answer

up vote 18 down vote accepted

They're called self drive types, and they're meant to be used as part of the oscillator:

piezo self-drive

The piezo effect works both ways: if you apply a voltage the piezo stretches, but also if it stretches it creates a voltage. This principle is used to create a feedback signal which drives the oscillator.
The advantage of the self drive is that it will automagically work at its resonance frequency, where it produces the loudest sound. In 2-wire circuits the oscillator's frequency is independent of the piezo's resonance frequency, and it's the designer who has to make that they're close.

For the piezo of your picture:

"G" = black
"M" = red
"F" = blue

(I guess M, F and G stand for Main, Feedback and Ground, resp. CMIIW)

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.