piezo-buzzer
Some time ago I've purchased Bestar Acoustic's F-B-P3009EPB-O1LF piezobuzzer, but only now found time to actually test it.
To my understanding, piezobuzzer should just work after voltage (in my case – 12V) is correctly applied, that is, produce tone of several KHz frequency.
At least, this is what my other KPEG272A piezo buzzer does, but with Bestar Acoustic's one I just hear single crackling, as if it were a loudspeaker.
Is my buzzer broken or my application of it is somehow wrong?
They're called self drive types, and they're meant to be used as part of the oscillator:
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)
The industrial PCB assembly process usually leaves residues — mostly soldering flux — on the circuit board. One step in the process is to wash the board (by dipping or spraying) with a solvent to remove those residues for long-term reliability and for the sake of appearance.
Some devices (such as sound or pressure transducers) have openings for their functioning, and their performance would be adversely affected if the solvent or the residues got washed into the opening and lodged there. Therefore, such devices often have a sticker that covers the opening(s) that should not be removed until after the washing.
Removing the stickers adds an extra step to the process, so for really high-volume manufacturing, it is often worthwhile to select parts that are declared "washable" to begin with.
Best Answer
This thing is not a "buzzer" it's a "sounder" in Chinglish or what I'd call a transducer.
It's actually a thin round piezoelectric "bender" element bonded to a metal backing that distorts in an "oilcan" mode when voltage is applied (image from here). That element is acoustically coupled to a Helmholtz resonant cavity.
Due to the "tuning" of the element and resonant cavity, the response of the "sounder" is not at all flat- it's really designed to emit the maximum sound level at a single frequency, in this case 2500Hz.
You will get the maximum sound level by driving it with a sine wave at that frequency and the maximum rated voltage, but a square wave will work too, since more than 80% of the energy of a square wave is at the fundamental frequency (but won't sound as pure because there is still some response from the transducer ('sounder') at, say 7500Hz.
You could create a 2500Hz square wave oscillator with a 555, or use a PIC or other microcontroller. If you use a microcontroller, you can drive the 'sounder' with two port pins push-pull, and so get almost 10Vpp drive from a 5V supply.
Here is an example of the latter type of circuit:
Where the "Alarm" is a piezo transducer.
The piezo element looks (electrically) like a capacitor (in this case, a 20nF capacitor) so the drive waveform from a PIC will be a bit trapezoidal (sloped rise and fall), but if you squint should look pretty much like a square wave.