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'[EE]: question about carbon microphones..'
2002\02\20@173159 by Chris Eddy

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I have a handset, identical to a regular telephone handset. It has one
of those carbon electret microphones in it. I cannot get any sort of
signal on my scope when I holler in the mic. I am used to the active
mics, like the two pin device that takes a 1K pullup to power it. Does
anyone know what sort of amplifier is necessary? Impedance of the mic
element? Gain that is necessary?

Thanks all
Chris~

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2002\02\20@174024 by Al Williams

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If it is really a carbon mic, you need to provide a voltage. It is just
a "sound-dependent resistor" so to speak. So try putting a voltage and a
resistor in series with it and measure the drop across the mic.

Al Williams
AWC
* Easy RS-232 Prototyping
http://www.al-williams.com/awce/rs1.htm



> {Original Message removed}

2002\02\20@174032 by Rick C.

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True carbon type elements are just nothing but carbon granules in a
chamber attached to a diaphragm(sp?). Sound waves vibrate the granules and
create a variable "resistance" representing the wave form hitting it. A
bias such as what you have in a conventional electret microphone will
provide sufficient "audio" to drive your application. A 1k bias "pullup"
resistor will work. (1k mic impedance)

Rick


Chris Eddy wrote:

{Quote hidden}

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2002\02\20@174306 by Eoin Ross

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They are effectively a carbon resistor that varies depending on the pressure in the diaphragm. To see a voltage change you'd need to place it in a voltage divider - a series resistor equivalent to the mikes resistance.

Need to go home - typed .com at the end of a sentence just now.

>>> .....ceddyKILLspamspam.....NB.NET 02/20/02 04:49PM >>>
I have a handset, identical to a regular telephone handset. It has one
of those carbon electret microphones in it. I cannot get any sort of
signal on my scope when I holler in the mic. I am used to the active
mics, like the two pin device that takes a 1K pullup to power it. Does
anyone know what sort of amplifier is necessary? Impedance of the mic
element? Gain that is necessary?

Thanks all
Chris~

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2002\02\20@174826 by Jim

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  "It has one of those carbon electret microphones
   in it."

Is it carbon - or is it an electret?

If it's carbon - it needs a bias to operate. Try
a 560 Ohm R to 5 volts.

It's bascialy a variable resistor. The old Motorola
2-way radios used to use carbon elements.

Jim

{Original Message removed}

2002\02\20@180428 by James Paul

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Chris,

A carbon mike has to have a voltage (current) source in series with it to
make it work.  It is basically a voice adjusted resistor.   Carbon granules
are packed inside the button on the back and the diaphram is connected
to a plate in fron of the button.  So at rest, it will have some
resistance. (Generally rather high  ie. several hundred Kohms to several
Megohms.)   So, with a battery and an ammeter in series with it, you
should see a varying current when the microphone is spoken into.
Feeding this varying current into a resistor and connecting an op-amp
across this resistor should give you a usuable output capable of driving
a hi-fi amp such as your stereo.

                                            Regards,

                                              Jim



{Quote hidden}

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2002\02\20@183226 by Chris Eddy

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Wow. that mystery was solved in a matter of minutes. Thanks for the
assist, all of you.

Chris~

Al Williams wrote:
>
> If it is really a carbon mic, you need to provide a voltage. It is just
> a "sound-dependent resistor" so to speak. So try putting a voltage and a
> resistor in series with it and measure the drop across the mic.

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2002\02\20@192733 by Vit

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Chris,

A carbon mic contains loosely packed carbon grains, and depending on whether
they are compressed or released by the membrane, its internal resistance
changes.  They do not produce electricity like other types of mic's, that's
why you didn't see anything on the scope.  Try to connect it like shown
below, and place oscilloscope probes in parallel with the microphone:

 ,------------<  +5V
   |

   R 100
   |
   |
  mic
   |
   '------------<  GND

Even though they are much noisier than other types of microphones, when I
was about 12, I preferred them over electret because I could get amplitude
modulation by simply plugging the mic in series with FM transmitter.
Electrets required a separate amplifier.

Hope this helps,

Vitaliy


{Original Message removed}

2002\02\21@090800 by Olin Lathrop

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> Even though they are much noisier than other types of microphones, when I
> was about 12, I preferred them over electret because I could get amplitude
> modulation by simply plugging the mic in series with FM transmitter.
> Electrets required a separate amplifier.

They also make a spectacular orange burst of flame about a meter long when
plugged into the 110V power line.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, RemoveMEolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2002\02\21@094808 by Alan B. Pearce

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>They also make a spectacular orange burst of flame about a meter long when
>plugged into the 110V power line.

ROTFLOL

New use for door entry intercom microphones when unwanted callers come ????

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2002\02\21@094820 by Chris Eddy

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Olin, don't tell me these things. You will awaken long past desires that
will get me in heap big troubles. I said that I would leave these fun
activities behind me long ago, for my safety and others. The lawyers
agreed. Hmm.. but you have me thinking.. I do have two of them..

Olin Lathrop wrote:
>
> They also make a spectacular orange burst of flame about a meter long when
> plugged into the 110V power line.

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2002\02\21@112334 by Herbert Graf

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IIRC a carbon mic can be simply thought of as a variable resister, so put a
low current through it and measure the voltage across it, it should
fluctuate with you voice. Try AC coupling to take out the DC bias that is
present, the variations may be very small. TTYL


> {Original Message removed}

2002\02\21@172317 by Peter L. Peres

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The carbon mike needs a good current through it to make it work. Try to
feed it through a resistor calculated for 20mA through the mike (from 12V
or such). The impedance is what you measure across the mike when biased,
in parallel with the bias R, plus a small capacitive parallel component
(<5nF afair). The output signal will be large (1 Vpp is easy at 1" from
speaker's mouth with the indicated bias circuit).

Peter

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2002\02\22@095520 by Chris Eddy

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Ok, yall, I got it to work. It works just as everyone advertised. It
does not help that the one of the two that I was working on was stone
cold dead.. And I did not think to swap them. Duh. As soon as I tried
the second one I had lots of complex voiceband waveforms.

Thanks all..
Chris~

"Peter L. Peres" wrote:
>
> The carbon mike needs a good current through it to make it work. Try to
> feed it through a resistor calculated for 20mA through the mike (from 12V
> or such). The impedance is what you measure across the mike when biased,
> in parallel with the bias R, plus a small capacitive parallel component
> (<5nF afair). The output signal will be large (1 Vpp is easy at 1" from
> speaker's mouth with the indicated bias circuit).

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2002\02\22@100252 by Max Toole

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In a message dated 2/22/02 9:55:47 AM Eastern Standard Time, spamBeGoneceddyspamBeGonespamNB.NET
writes:

> Ok, yall, I got it to work. It works just as everyone advertised. It
>  does not help that the one of the two that I was working on was stone
>  cold dead.. And I did not think to swap them. Duh. As soon as I tried
>  the second one I had lots of complex voiceband waveforms.
>
>  Thanks all..
>  Chris~
You may be able to rejuvenate the bad one by taking out the element and
hitting it on the table to loosen up the granules.
Max

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2002\02\22@123037 by Chris Eddy

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Max Toole wrote:
> You may be able to rejuvenate the bad one by taking out the element and
> hitting it on the table to loosen up the granules.
> Max

Ahah! now I know why my wife always beats the receiver on the table when
we are talking. She is trying to rejuvenate the mic element. Shouting
into it must do that too, she does a lot of that.

Chris~

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2002\02\23@052949 by Russell McMahon

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> >They also make a spectacular orange burst of flame about a meter long
when
> >plugged into the 110V power line.
>
> ROTFLOL
>
> New use for door entry intercom microphones when unwanted callers come
????
>


Hey Dukey. Pick up da phone!

Wazzzzzzzzzzuuuuuuuuuup

Boom!

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2002\02\23@053007 by Russell McMahon

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> Olin, don't tell me these things. You will awaken long past desires that
> will get me in heap big troubles. I said that I would leave these fun
> activities behind me long ago, for my safety and others. The lawyers
> agreed. Hmm.. but you have me thinking.. I do have two of them..
>
> Olin Lathrop wrote:
> >
> > They also make a spectacular orange burst of flame about a meter long
when
> > plugged into the 110V power line.


Transistors (metal can) in power points.
Tinfoil in lightbulbs
Nitrogen tri-io ......   in .................. (ubiquitous)

Hard hats, body armour, Lexan (tm) shields & eye protection all obligatory
Don't try this at home.
Not for on road use
Do not spindle fold or mutilate
Have a nice day
..................................

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2002\02\23@060440 by Peter L. Peres

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>They also make a spectacular orange burst of flame about a meter long
>when plugged into the 110V power line.

How do you know that ? ;-). At 220V they make a green-orange burst and
lots of stinking smoke (probably green from copper and chlorine vented by
burning PVC). This can hit you in the face if the unit is being held while
trialwise plugging wires in a box ...

Peter

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2002\02\23@090907 by Olin Lathrop

face picon face
> >They also make a spectacular orange burst of flame about a meter long
> >when plugged into the 110V power line.
>
> How do you know that ?

How do you think!?

Back in college around 1976 or so, I ended up with a junker phone for some
reason.  I don't remember what prompted it, but I think someone made some
claims about phones and 120V AC lines that I thought were ludicrous.
Eventually it was agreed the argument could be settled by whether the carbon
mouthpiece could withstand line voltage.  I knew it couldn't, so I soldered
the ends of a power cord to it, shut off the circuit breaker, and plugge in
the mic.  The outlet and the breaker box were in the same hallway, about 30
feet apart.  A crowd stood by the breaker box as I flipped the breaker.
BOOM!  Even more impressive than I had expected.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, TakeThisOuTolinEraseMEspamspam_OUTembedinc.com, http://www.embedinc.com

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2002\02\24@200533 by Russell McMahon

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> >They also make a spectacular orange burst of flame about a meter long
when
> >plugged into the 110V power line.
>
> ROTFLOL
>
> New use for door entry intercom microphones when unwanted callers come
????
>


Hey Dukey. Pick up da phone!

Wazzzzzzzzzzuuuuuuuuuup

Boom!

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2002\02\24@200546 by Russell McMahon

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> Olin, don't tell me these things. You will awaken long past desires that
> will get me in heap big troubles. I said that I would leave these fun
> activities behind me long ago, for my safety and others. The lawyers
> agreed. Hmm.. but you have me thinking.. I do have two of them..
>
> Olin Lathrop wrote:
> >
> > They also make a spectacular orange burst of flame about a meter long
when
> > plugged into the 110V power line.


Transistors (metal can) in power points.
Tinfoil in lightbulbs
Nitrogen tri-io ......   in .................. (ubiquitous)

Hard hats, body armour, Lexan (tm) shields & eye protection all obligatory
Don't try this at home.
Not for on road use
Do not spindle fold or mutilate
Have a nice day
..................................

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2002\02\24@201159 by Sean H. Breheny

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LOL!

At 10:55 AM 2/22/02 +1300, you wrote:
{Quote hidden}

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