Using Carbon Microphone with Teensy 4.0

M

MeatySteak

New member
Hi,

I’m looking into repurposing an old rotary phone that I have with a teensy 4.0. I’ve been following this tutorial:


In the tutorial, the microphone he is using is what I believe to be a carbon microphone. From what I can tell, everything seems to be a matter of connecting the microphone to the mic and gnd pin on the teensy adaptor and he is able to use the sound from the original headset microphone. From the limited information I’ve gathered online however, people seem to suggest that shouldn’t work?

I have a similar set-up (not the same phone but it utilizes a carbon mic) and want to know how this works because I dont understand how he has magically made it work? Maybe I’m missing something?

I have the option to swap it out for an electronic microphone (linked below) but I’m kind of in the mindset of, “if it aint broken, dont fix it” and would rather not spend the money if I can help it.


All help is appreciated, but please address the questions I have asked. “Suggestions” on how I “should be doing this” because its more efficient or for whatever reason will be ignored as I want to keep the phone true to its original parts if I can help it. If it is operationally required that I do something different or else it wont work, then please tell me. Otherwise, bug off.

FYI, I do not have the teensy yet as I want to make sure that this is capable of working before buying parts that may become useless to me.

Thanks
 
Carbon mics require a bias voltage - so the bias on the Audio adaptor (for an electret mic) ought to produce some output. I suspect its very low compared to what the mic is designed for. Carbon mics are awful BTW, use an electret instead is my advicel
 
MarkT said:
Carbon mics require a bias voltage - so the bias on the Audio adaptor (for an electret mic) ought to produce some output. I suspect its very low compared to what the mic is designed for. Carbon mics are awful BTW, use an electret instead is my advicel
Click to expand...
Yeah, so after getting to know thoroughly how old rotary phones work and becoming an absolute expert on the matter (an exaggeration but you get the idea, I know this phone forward and backward now), but yeah I figured there had to be some minute form of bias voltage coming from the shield.

My follow up questions are in regards to the electret mic as you said.
1) The one that I have linked, is that an electret? My impression says yes as that makes the most sense, but I chucked it through chatgpt (reliable I know) and it seems to think its a dynamic mic? I know it doesnt make a huge difference in terms of set-up, more curiosity than anything.
2) These are mics I am not familiar with so just want to confirm the requirements for them. From what I know, Dynamic mics dont really require any supply voltage? And electret are similar to carbon where they need a low bias voltage? So its more just integrating with the teensy itself and is there anything additional that I need for the teensy to read the signals from the mic? Im assuming no since it would just be an analog signal like the carbon?

Thanks for your help!
 
A carbon microphone is a variable resistor, so hopefully that will help you to utilise it. Originally it would have a 50V power supply.
 
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