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

[Matteo Sisti Sette]

By the way, thinking about it again, I think the sound card applies a DC 
voltage to its input (about 3V) (in order to polarize an electret 
microphone), so I'm afraid the parallel diodes can't work because the 
one pointing downwards would always be "on".........

On 04/21/2012 05:03 PM, Martin Peach wrote:
> On 2012-04-21 10:16, Matteo Sisti Sette wrote:
>> On 04/21/2012 12:38 AM, Martin Peach wrote:
>>> You could put a resistor in series to limit the current or a pair of
>>> diodes in parallel to clamp the voltage. Probably a pair of 1N4001s like
>>> this would work:
>>>
>>> IN---+------+-----OUT
>>> | |
>>> ^ v
>>> | |
>>> GND--+------+-----
>>
>> Hi,
>>
>> Thanks for the suggestion. If I understand correctly, here the
>> non-ideality of the diodes is what does the trick, and this would limit
>> the voltage to below the diode's drop, right? which is about 1V or so...
>>
>> Now, thinking about it, wouldn't the following be even better? (this
>> hadn't come to my mind before)
>>
>> IN---+------+-----OUT
>> |
>> v
>> |
>> |
>> ^
>> |
>> GND--+------+-----
>>
>> with two ZENER diodes of appropriate reverse voltage? Facing each other?
>>
>> So within the "allowed" voltage range there would be no (or much less)
>> distortion?
>>
>> Maybe I'm being too naive here?
>>
>
> Yes that's the next step, if you want a larger voltage range. Or use
> strings of ordinary diodes to add about .6V per diode. I think if you
> only want to detect hits it doesn't matter too much. Ideally, you would
> know the voltage range of your audio input and set the levels to fit that.
>
> Martin
>