[PD] (OT) safely connect piezo transducer to soundcard as microphone

Matteo Sisti Sette matteosistisette at gmail.com
Sat Apr 21 20:11:37 CEST 2012

On 04/21/2012 05:31 PM, Martin Peach wrote:
> That sounds unlikely. If it had 3V on the input you would always get a
> high value with nothing connected.

I measured it with the tester and it's there. The soundcard has a 
highpass filter which removes DC so you don't "get" it.

> Anyway, it's better to use a line
> input with piezos because their output is in volts, not millivolts.

Actually my notebook has only one connector for input. I always guesste 
it could work both as mircophone and as line in, but I cannot find a 
settings for this in Ubuntu's sound settings. There's only an "input 
level" for microphone which is not clear whether it's hardware or 
software (also, it ranges from "unamplified"  to "100%" - LOL)......

> If it really has 3V on it, putting a 10k resistor in series with the
> input will protect it and still pass the piezo signal, which is very
> high impedance, so won't be diminished much:
> IN----+----+----/\/\/----OUT
> | |
> ^ V
> | |
> GND---+----+-------------

That will certainly protect the soundcard, but will it prevent the 
right-hand diode from being forward biased all the time killing the 
microphone signal?

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