I have a number of loose piezoelectric diaphragms (for buzzer alarm) which I wish to test. I understand this must take place with an AC voltage source. Can I use the headphone output of my laptop - 4V AC?

Do I have to place the diaphragm on a metal base for the test, or can I test them just as they are?

 

The headphone output sound just about perfect. Some piezo elements can withstand more voltage than that and will be louder at the higher voltage. There are a few piezo elements that are not rated for very large voltages but I doubt that you will damage any that you have with the 4 volt drive.

You may or may not need to put the diaphragms on a metal plate but you do have to get connections to the metal on both sides of the diaphragm.
How the diaphragm is mounted will make a huge difference in how loud the sound is. The diaphragm is loudest at mechanical resonance.

Do you have pictures or data sheets for the diaphragms? Either one would make the answers much better. If you take a picture then make sure that you include a size reference or tell us what size the elements are.

 

Apply audio from a home stereo speaker terminals and feed the amplifier input with a variable oscillator perhaps from some laptop generator application. The laptop output may be too weak for the piezoelement buzzer to be evaluated.
An AC voltmeter in parallel can show the resonant frequency. If suspended in air instead of placed in resonator cavity or on top of a surface will change its volume.

 

Sorry, I forgot the fotos. The "discs" are 15 and 20mm respectively. Unfortunately, I have no data sheets.
Just checked the lap top outputs: The micophone output is 2.3V DC (not 4V AC!!!)!, and there seems to be no voltage on the headphone.

 

Hello,

Have a look at the following PDF:
http://educypedia.karadimov.info/library/7bbappl.pdf

Bertus

 

Thanks, Bertus (I like your cat).

I know that link, but don't quite understand all about the importance of Node, Edge, or Central support possibilities, because everyone seems to talk about gluing the back of the diaphragms DIRECTLY onto the inside of the watch case, ie flat and supported all over the disc.
Bob

 

The thickness and flexibility of a watch case has a big influence on the piezoelement response.
A laptop microphone connection is an input, not an output; and the earphone connection has to be measured with an AC voltmeter with audio being outputted.

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The circuit here oscillates at about 600 Hz. The peak to peak amplitude is about 9 volts ... more or less the same as 4 vac. ... operates from a 9 volt battery.