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

richard duckworth richduckworth at yahoo.com
Sat Apr 21 20:33:05 CEST 2012


If you add an electrolytic coupling capacitor to that schematic before it goes into the soundcard it will block any DC 'electret powering' voltage and prevent it from getting back into your piezo circuit. A 1uF should do it.  
 
Rich Duckworth
Lecturer in Music Technology
Department of Music
House 5 
Trinity College 
Dublin 2
Ireland


Tel 353 1 896 1500


It's the most devastating moment in a young mans life, when he quite reasonably says to himself, "I shall never play The Dane!"


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Sent: Saturday, 21 April 2012, 16:32
Subject: Pd-list Digest, Vol 85, Issue 65
 
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Today's Topics:

   1. Re: trying to track down a bug: Pd-extended 0.43-1 beta on
      Oneric 32 bit (Hans-Christoph Steiner)
   2. Re: [PD-announce] leer este             07 (laura plana)
   3. Re: (OT)
 safely connect piezo transducer to soundcard as
      microphone (Matteo Sisti Sette)
   4. Re: (OT) safely connect piezo transducer to soundcard as
      microphone (Matteo Sisti Sette)
   5. Re: HID double triggers (James Dunn)
   6. Re: (OT) safely connect piezo transducer to soundcard as
      microphone (Martin Peach)
   7. Re: (OT) safely connect piezo transducer to soundcard as
      microphone (Matteo Sisti Sette)
   8. Re: (OT) safely connect piezo transducer to soundcard as
      microphone (Martin Peach)


----------------------------------------------------------------------

Message: 1
Date: Sat, 21 Apr 2012 09:42:28 -0400
From: Hans-Christoph Steiner <hans at at.or.at>
Subject: Re: [PD] trying to track down a bug:
 Pd-extended 0.43-1 beta
    on    Oneric 32 bit
To: IOhannes m zmoelnig <zmoelnig at iem.at>
Cc: pd-list at iem.at
Message-ID: <65D79887-DF07-435A-85DB-EC0F96F9B59C at at.or.at>
Content-Type: text/plain; charset=us-ascii


On Apr 21, 2012, at 9:09 AM, IOhannes m zmoelnig wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On 2012-04-16 20:44, John Harrison wrote:
>> Sorry for the delay on this. I downloaded today's binary build of
>> Pd-extended for Ubuntu 11.10 32 bit, then ran Pd-extended with -nrt in
> 
> is it possible to build Gem (from the git "master" branch)
 yourself?
> what is the exact version it shows for Gem?

Gem in Pd-extended is the 0.93 branch, at commit 1458b4f8cfa12503bba94e2a8804f802f07efdaa

http://pure-data.svn.sourceforge.net/viewvc/pure-data/branches/pd-extended/0.43/externals/Gem/

.hc




----------------------------------------------------------------------------

                            kill your television





------------------------------

Message: 2
Date: Sat, 21 Apr 2012 14:47:54 +0000
From: laura plana <lauraplanagracia at hotmail.com>
Subject: Re: [PD] [PD-announce] leer este         
    07
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href="iucogeduraadaponer.y56.info/eS/?msg=diezajase3fj&p=pd-announce at iem.at" >
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Message: 3
Date: Sat, 21 Apr 2012 16:16:17 +0200
From: Matteo Sisti Sette <matteosistisette at gmail.com>
Subject: Re: [PD] (OT) safely connect piezo transducer to soundcard as
    microphone
To: Martin Peach <martin.peach at sympatico.ca>
Cc: PD-List <pd-list at iem.at>
Message-ID: <4F92C131.1030505 at gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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?



------------------------------

Message: 4
Date: Sat, 21 Apr 2012 16:24:52 +0200
From: Matteo Sisti Sette <matteosistisette at gmail.com>
Subject: Re: [PD] (OT) safely connect piezo transducer to soundcard as
    microphone
To: pd-list at iem.at, richduckworth at yahoo.com
Message-ID: <4F92C334.9090103 at gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

On 04/21/2012 02:14 AM, richard duckworth wrote:
> Piezo mics should go through a very high impedance buffer stage.
> ......

Thank you very much, that was illuminating.

However for now I'm was looking for a simplistic solution without the 
slightest care for sound quality, as I'm just using the signal to take 
its envelope in order to detect knocks and the like.

But now I know why it sounds the way it sounds and that with an 
appropriate high impedance buffer stage it can sound way better, the day 
I'll need it :D





------------------------------

Message: 5
Date:
 Sat, 21 Apr 2012 15:22:22 +0100
From: James Dunn <james at 4thharmonic.com>
Subject: Re: [PD] HID double triggers
To: IOhannes m zmoelnig <zmoelnig at iem.at>
Cc: pd-list at iem.at
Message-ID: <4F92C29E.5000703 at 4thharmonic.com>
Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"

Quoth IOhannes m zmoelnig, on 21/04/2012 14:23:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 2012-04-18 20:27, Andrew Faraday wrote:
>> I've had this problem before with [hid], apparently it's a hardware
>> issue called 'debouncing', which is often ignored
 because it is often
>> irrelevant (pushed is pushed, for game controllers, rather than a
>> button-on/button-off signal used for most music systems).
>>
>> You can deal with the problem in pure data by using a trigger, float and
>> delay of one millisecond. See the attached patch, click the message
>> boxes and watch your terminal for the result.
> [change] seems to be the more appropriate solution here...
>
> fgmasdr
> IOhannes

Thanks for the suggestion. The problem I have with these two solutions 
is that they only work when the double triggers are in sequence. 
Sometime they arrive like this:

[hid] 0.7, written by Hans-Christoph Steiner <hans at eds.org> 
<mailto:hans at eds.org>
     compiled on Apr 15
 2012 at 08:12:47
[hid] opened device 4 (/dev/input/event4): AT Translated Set 2 keyboard
print: key key_j 1
print: key key_l 1
print: key key_j 1
print: key key_l 1
print: key key_j 0
print: key key_j 0
print: key key_l 0
print: key key_l 0

So I would need to store the value of each key individually and check 
each one with [change].
Instead of this long-winded method, I've downloaded [linuxevent] which 
is working nicely so I think I'll stick with this even though it may be 
deprecated?

Surely this is a bug with [hid] though?

James
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Message: 6
Date: Sat, 21 Apr 2012 11:03:25 -0400
From: Martin Peach <martin.peach at sympatico.ca>
Subject: Re: [PD] (OT) safely connect piezo transducer to soundcard as
    microphone
To: Matteo Sisti Sette <matteosistisette at gmail.com>
Cc: PD-List <pd-list at iem.at>
Message-ID: <BLU0-SMTP534D94809FC233CDA94E87ED230 at phx.gbl>
Content-Type: text/plain;
 charset="ISO-8859-1"; format=flowed

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



------------------------------

Message: 7
Date: Sat, 21 Apr 2012 17:07:12 +0200
From: Matteo Sisti Sette <matteosistisette at gmail.com>
Subject: Re: [PD] (OT) safely connect piezo transducer to soundcard as
    microphone
To:
 Martin Peach <martin.peach at sympatico.ca>
Cc: PD-List <pd-list at iem.at>
Message-ID: <4F92CD20.7050907 at gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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
>




------------------------------

Message: 8
Date: Sat, 21 Apr 2012 11:31:28 -0400
From: Martin Peach <martin.peach at sympatico.ca>
Subject: Re: [PD] (OT) safely connect piezo transducer to soundcard as
    microphone
To: Matteo Sisti Sette <matteosistisette at gmail.com>
Cc: PD-List <pd-list at iem.at>
Message-ID: <BLU0-SMTP92CD4B67CD820FF6D452E2ED230 at phx.gbl>
Content-Type: text/plain; charset="ISO-8859-1"; format=flowed

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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