Piezo To Detect Sound

[Rajinder]

Hi,
I am considering a project where i can use a piezo buzzer to detect sound rather than using a mic. I have seen different types of piezo buzzers, some with 2 wires and some with 3 wire. I think that the 3 wire has an additional feedback signal. Not sure.

Is this a possibility? I am trying to detect vibrations as if someone is trying to smash a glass or window i.e. security for the home.

Does anyone have any ideas on how this can be done. I was thinking piezo , with a pre-amplifier, peak detector and then comparator into a microcontroller.

Any help would be very much appreciated.

Best regards,
raj

 

[Sunnysky]

a buffered piezo mic = std. electret mic has the better EMI immunity. Use that instead.

 

[AnalogKid]

Also recommend an electret mic cartridge over a piezo disc.

And - if you talk with the people who make glass break detectors for home and commercial security systems, you lean stuff. For example, there is a large, very-low-frequency component to the sound of glass breaking, and that is the signature these detectors use so they don't false-trip on normal room sounds.

ak

 

[Rajinder]

ok thanks for your assistance. so an electret mic, amplifier and comparator or similar woul ddo the trick?

 

[AnalogKid]

That is the basic signal path to start. You probably will wind up adding filters or a rate limiter.

ak

 

[Colin Mitchell]

We use a piezo as a contact mic to hear right through glass with our wall bug transmitter. A bit tinny but as clear as a bell.

 

[cl10Greg]

Usually goes mic -> filter -> amplifier -> comparator. If you have the filter after the amplifier, you also amplify the noise

 

[Herschel Peeler]

Also recommend an electret mic cartridge over a piezo disc.

And - if you talk with the people who make glass break detectors for home and commercial security systems, you lean stuff. For example, there is a large, very-low-frequency component to the sound of glass breaking, and that is the signature these detectors use so they don't false-trip on normal room sounds.

ak

How low a low frequency component?

 

[AnalogKid]

1 Hz-ish