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Can a telephone carbon microphone be used with a computer? Answered

I want to use an old 50's telephone handset with my computer for making phone calls with gmail. I know the receiver/speaker will work, but will the carbon microphone work if connected directly? I seem to have come across a few things stating that it will work if connected directly and others that say that a battery or resistor or both is needed. Thanks for any info.



7 years ago

The signal level from a carbon microphone + battery is much stronger than the modern electret mic. You may even power the sircuit from the USB plugs.
This sircuit: http://tinyurl.com/phcev makes you use a telephone as headset for e.g. skype.


Thank you all for the information.

The answer to the question of, can a old carbon microphone be connected directly to the microphone input on a computer sound card, the answer to this is no. The microphone input on a computer sound card is expecting an electret condenser microphone.

As others have pointed out, a carbon microphone is something different, electrically. Via the Wikipedia article on "carbon microphone", I found a link that containing circuit diagram explaining how these things should be wired, in figure 3 of this document:

Of course there are other tricks. 

You could just remove the old carbon microphone from your handset and replace it with an electret microphone. That would probably be the easiest thing to do.

Also if you happen to have the whole phone you might be able to tie it in by connecting it through another, more modern POTS phone.
Like this answer:
And this instructable:


It's going to be a pretty shoddy microphone, by today's standards. But it should be sufficient for phone-quality sound.

The carbon mike works as a variable resistor that is varied by the sound. therefore you need a suitable power supply with the microphone in series with it.

a single AA battery may do the trick.