On 2012-04-21 11:07, Matteo Sisti Sette wrote:
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".........
That sounds unlikely. If it had 3V on the input you would always get a
high value with nothing connected. Anyway, it's better to use a line
input with piezos because their output is in volts, not millivolts.
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---+----+-------------
Martin
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
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