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Topic: piezo element with 3 wires (Read 3294 times) previous topic - next topic

action_owl

I have a bunch of piezo buzzers that I salvaged from some older smoke detectors they have 3 wires:
red, black and white.

If I just use red and black it works but I was wondering what the white might actually be for?
I had always assumed it was ground but then why would you need something like this:

http://www.uoguelph.ca/~antoon/circ/at121.html

the extra wire in that schematic is labeled as "feedback"?

westfw

The "feedback" lead permits you to build oscillators that "automagically" run at the ideal frequency (and thus maximum volume) for a particular piezo element without having to have any timing elements in the circuit itself (other than the piezo itself, which is not dissimilar from a giant crystal.)

action_owl

thanks for that knowledge nugget westfw,

that makes perfect sense for a smoke detector buzzer to play at the loudest possible volume.

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