"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 -----
From: "Chris Eddy" <ceddy@NB.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, February 20, 2002 3:49 PM
Subject: [EE]: question about carbon microphones..


> 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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