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?