Hi,
This is OT but I'm sure many of you have used piezo microphones sometimes.
I've often connected a piezo transducer to the microphone input of my computer (and other computers) by simply soldering the two wires to the T and S of a minijack plug, and it works just fine and my soundcard hasn't suffered any damage (apparently at least).
However, I am concerned that a strong sound input (e.g. hitting the piezo transducer with with fair strength) may actually generate a voltage peak (thought only for a short time) capable of damaging the soundcard, couldn't it?
Also, a friend of mine did the same with his Macbook and his headphones output has stopped working (may be just a coincidence though).
Is there an easy way to make it safer? I seem to remember I had read somewhere (can't find it) about connecting a 1MOhm resistor in parallel... woudl that do the trick?
thanks m.
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--+------+-----
Martin
On 2012-04-20 18:12, Matteo Sisti Sette wrote:
Hi,
This is OT but I'm sure many of you have used piezo microphones sometimes.
I've often connected a piezo transducer to the microphone input of my computer (and other computers) by simply soldering the two wires to the T and S of a minijack plug, and it works just fine and my soundcard hasn't suffered any damage (apparently at least).
However, I am concerned that a strong sound input (e.g. hitting the piezo transducer with with fair strength) may actually generate a voltage peak (thought only for a short time) capable of damaging the soundcard, couldn't it?
Also, a friend of mine did the same with his Macbook and his headphones output has stopped working (may be just a coincidence though).
Is there an easy way to make it safer? I seem to remember I had read somewhere (can't find it) about connecting a 1MOhm resistor in parallel... woudl that do the trick?
thanks m.
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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?
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
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
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
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?
Hi,
A piezo transducer often produces a signal level somewhere inbetween mic level and line level (it depends on size, and method of excitation). Indeed it can be too loud when mic input is used.
Another point of concern is impedance, which influences the sound character. If you mount a resistor (in series), the signal level is reduced but the sound is altered as well. Mounting a capacitor (in parallel or series) also works to reduce signal level and alter the sound. Combinations of these (RC networks, effectively) are a great way to tune the sound character to your liking, but it takes a lot of experimentation. Also, the result may be different for each (mic) preamp because input impedance is not fully standardized.
Katja
On Sat, Apr 21, 2012 at 12:12 AM, Matteo Sisti Sette matteosistisette@gmail.com wrote:
Hi,
This is OT but I'm sure many of you have used piezo microphones sometimes.
I've often connected a piezo transducer to the microphone input of my computer (and other computers) by simply soldering the two wires to the T and S of a minijack plug, and it works just fine and my soundcard hasn't suffered any damage (apparently at least).
However, I am concerned that a strong sound input (e.g. hitting the piezo transducer with with fair strength) may actually generate a voltage peak (thought only for a short time) capable of damaging the soundcard, couldn't it?
Also, a friend of mine did the same with his Macbook and his headphones output has stopped working (may be just a coincidence though).
Is there an easy way to make it safer? I seem to remember I had read somewhere (can't find it) about connecting a 1MOhm resistor in parallel... woudl that do the trick?
thanks m.
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katja -
Martin Peach -
Matteo Sisti Sette