Carbon Charcoal Microphone

Carbon inside of a cup can be used a make a variable resistance microphone. This video was made at the Exploratorium Teacher Institute.

[@WVmedia]

More simple:A battery in series with the microphone and then connect this to a loudspeaker (without an amplifier).If the microphone works,this will work.

[@Karlfalcon]

The fact that this readily worked without intentionally adding a battery or other power source to the circuit seems to indicate that there is a DC bias inherent in the input to the computer speakers that were used. To do this properly you need a power supply - preferably variable, since that would let you adjust the mic sensitivity to some degree. That said - a superb project! I would have loved to have done this as a kid.

[@atomicsteameng]

Karlfalcon I've seen those speakers before (Not the exact ones that he has in the video, just the type) and if I remember correctly, for them to work, you need to put in some batteries.

[@tookitogo]

@@atomicsteameng Yes, that's obvious, but it's also not what he was saying. He's saying that the speakers are actually allowing some electricity to flow _out_ of the inputs - a flaw that's inadvertently allowing this microphone to work without its own power supply.

[@dwilder1667]

I couldn't get this to work without a battery (other than some static). I tested the input jack to my speakers and did not see any power out AC or DC across any combination of contacts. Maybe something is wrong with my speakers (they're cheap). I did get it to work though. This is what I did... I put a 9V battery going through the mic. + before mic, - return from speaker jack. I crushed the carbon to a finer grind (in coffee mug with chisel handle). I used 3 cups. Two as shown and a third as diaphragm with a plastic bead glued to the bottom to transfer vibration to the inner cup. I tinkered with how much carbon, compression of carbon and how tightly to press the bead against the middle cup and found a sweet spot where all worked. I tested the output by recording the speaker with my phone isolated in an ice chest just to make sure I was really getting audible sound, not just static. I tried it with a small unpowered 8ohm speaker and could only get muffled static but that should work in theory.

[@WVmedia]

You will get better results when you use a battery(4,5V max) in series with the mike and then connect this to a transformer.High imp. to the amplifier.

[@_bjorken]

Good video! Though how did you make it work without a power source? Where does the current come from? Im confused.

[@Origoangelohrol322]

It can't work without a DC bias. I don't know how it's working on the video but you need a DC bias. I suggest connecting a battery with a series resistor to the microphone and then like in the video connect the microphone to the speakers input. Then the changing resistance of the microphone will produce a change in the voltage across it which can be amplified by the speakers's amp. You'll have to try with different resistor values to get the maximum sensitivity. I suggest 1k resistor for 4.5V battery as a start.

[@theLuigiFan0007Productions]

Some sets of cheap speakers have leakage on their input side. Due to this, it's probably why the microphone is working.

[@ysvsny7]

Thank you. Very informative

[@faringo12]

Thanks !! Very good job! :)

[@ronhummel9298]

Hello- I am interested in rebuilding a non-working carbon microphone element. Two questions: 1) Which activated carbon is more effective, small granules or finely ground carbon dust? 2) Is voltage from a computer USB port adequate? (About 5 VDC) Ron Hummel Vintage Microphones

[@joseantoniootero8051]

Usa el carbon de una pilas viejas, lo lavas lo haces granito, y listo

[@theholykaremtheholyshibe2029]

GREAT 👍 HISTORY Lesson

[@eduardomercado]

hi, I have a doubt, the current that pas througt the carbon is higer when que carbon is expanded or when the carbon is with press?

[@tookitogo]

When compressed, the resistance goes down, which in turn allows current to go up.

[@mycamguy]

Cool

[@MoveP3]

well- looks good and reliable, but itdoesn't work!!

[@Jeffrey314159]

4:29 No sh!t Sherlock