attempting to understand piezo sensors

Hi folks – I’m a longtime programmer, but a noob with electronics. I’m attempting to build the “knock” tutorial. But, before I do, I want to understand how/why a piezo buzzer can work as a variable-voltage input sensor.

I’d like to build a very simple circuit in which I could connect my piezo to my multimeter and watch the voltage spike as its hit. Based on the (very fuzzy unclear) graphic on the knock page, I’ve tried to do this by just placing a 1Mohm resistor in parallel to the piezo. But I’m still reading aboslutely nothing on my multimeter, in DC or AC.

I know I must be missing something simple. Can any circuit-heads shed light on this for me?

Thanks!

=T=

I don't know much about this topic but I suppose that the spike will be too short for the multimeter to register it. It's only a knock, right? And there's no voltage on a piezo buzzer at rest.

The pulse will be too short for the multimeter to respond to. Do you have any other test gear?

:o OH that totally explains it.

is there some other kind of test equipment that would register it?

i'll just try it directly in the arduino now and see how that works.

thanks!

is there some other kind of test equipment that would register it?

You could always just make your own test equipment: The Piezotestduino?

Ehheh. Seriously though. I do not know of any equipment that would detect it. Maybe an oscilliscope? :-[ I do not know...

ok, the piezotestduino it is.

i think part of why i assumed it would work with a multimeter is that i know people use piezos to make contact mics. so that suggests that if you scratch on the surface of a piezo, instead of just thwapping it, it ought to produce a continuous voltage level...

is there some other kind of test equipment that would register it?

An oscilloscope would be able to display the signal from the piezo, but if you want to show a non-repeating waveform (i.e. a single strike), you'll need a storage scope.