| Author | Message | ||
     Arkenstone |
Is it possible to use some kind of microphone to vary the resistance of a circuit when the amplitude of sound varies? I need to build a microphone which varies its resistance when there is a sound - the easiest way out seemed to be building a carbon mic (as most old phones operate) but these microphones have become so absolete that I am finding it hard to obtain adequate information in order to be able to build one myself. Can I use any other type of microphone which is commonly used nowadays such as dynamic or electret and attach it to some basic circuit so that I'd be able to vary the resistance of in another circuit. By the way the other circuit is going to be a computer game-port which monitors changes in resistance - that's why I am insisting so much on resistance. Thanks in advance. | ||
| Simon Quellen Field (Sfield) |
It is easy to make a carbon microphone. You can simply place a graphite pencil lead on a couple of wires and place the whole setup on a cardboard box. But it won't work with your computer. The resistance is going to vary with the frequency of your voice, say from 50 times per second to 10,000 times per second. The computer is expecting a resistance that varies at most once or twice a second. You can build a more elaborate circuit that detects the amplitude of the sound, and uses that to control the base of a transistor, making the transistor into a variable resistor. But I suspect you will want some electronics courses before you tackle that particular design task. | ||
| darkenstone |
Actually I think I'd be able to poll this device at higher frequencies (I was able to poll my version of carbon mic at 1khz). Moreover, to reveal the whole story underneat ;) , I don't need this mic to record human voices but I am trying to build a simple electronic drum which just detects the hitting of the sticks on some pad underneat which there will be this carbon mic connected to the computer. Then THe computer will generate a some percussion instrument sound corresponding to the change in resistance registered( but the last part is all programming and you won't be concerned). I have already created the circuit to the computer, all I need is some sensitive carbon mic cause the one I have built was not sensitive. I had to actually hit !! the carbon mic for it to allow enough current to pass through(if i do so its life span will decrease a lot) . BTW my carbon mic is one which uses carbon granules and diaphragm. Probably my problem was the choice for the material of the diaphragm. FIrst I used alum foil (the kitchen foil) because some physics book said that it can be made of a thin layer of aluminium. Then I tried using some sort of very thin plastic, similar to the kind used in plastic-bags. None of these worked well but hopefully tomorrow I will try using that kind of very thin leather used in real drums (cause I think it has to be some kind of elastomer). Do you think there is some better material for the diaphragm? and another simpler (i suppose) question: I am creating my carbon graphite by using the carbon rod found inside the battrey and breaking it to very very small pieces. Is this allright? Regarding the method you suggested I think it might be quite an easy and good alternative to using carbon granules and diaphragm but I have got to use the diapgragm since my project is actually there to demonstate that longitudonal sound waves will make the diaphragm vibrate and thus varying resistance. Excuse me for the lengthy (hope wasn't boring ;)) explanation and thanks a lot. | ||
| Simon Quellen Field (Sfield) |
The cardboard box is the diaphragm in the design I described. Do a Google search for "homemade carbon microphone" and you will find one that claims to be able to hear a fly walking on the box. I would use crushed pencil leads. A cheap package of mechanical pencil leads, a hammer, and a plastic bag... Many companies use cheap piezoelectric elements (like those for making tinny noises in cheap toys and greeting cards) as the drumhead. When you hit one, it generates a spike of current that the computer can see on a normal digital input pin (like a game port button or trigger). I think Radio Shack still sells them. | ||
| arkenstone |
I think I am going to use the method you suggested because the carbon graphite will eventually settle after some time if the microphone is not continuosly in motion as was the case of the telephone receiver. The carbon rod method doesn't seem to have this problem so it will be better. THis is the method you are suggesting, isn't it? Thanks a lot |
