Attenuating piezo sounder for testing purposes

[sjb741]

I have a commercial smoke detector which I'd like to use for experimental purposes. It uses a soic-16 chip by "SEMIC": CS2105AGQ-S1Z, TGAY2VU401L.

The piezo sounder is the type with 2 terminals (ground, brass and silver <--> ground, drive, feedback ?).

If the piezo has a resonant driver circuit (I can't tell, but it does use 3 wires) then I think brass is 'drive' and silver is 'feedback'. Or maybe it is simply driven by an H-bridge.


The piezo volume can be somewhat attenuated simply by squeezing between thumb and finger.

Ideally though I would like to be able to smoothly vary the volume. I was wondering whether a simple 'rheostat' in series with ground would work and if so what a sensible value would be?

 

[FvM]

If the piezo sounder is a passive transducer (two terminals), a variable series resistor should work. For a transducer with feedback electrode (three terminals) or built-in oscillator (DC supplied), it doesn't.

 

[D.A.(Tony)Stewart]

Tape over the hole works well.

 

[sjb741]

It has 3 wires. I snipped the ground wire, and now I hear a muted 'buzz' which is acceptable.

Physic

 

[FvM]

now I hear a muted 'buzz' which is acceptable.

Fine. Possibly the best result you can achieve. The three terminal piezo is part of the oscillator circuit. Some modifications, e.g. series resistors might stop it.