Computer Science Project



About microphones

It's important to say some words about microphones because the project uses a microphone to capture the noise. Microphones transform the acoustical energy into electrical energy. When we speak the sound waves generate into the diaphragm (piece of plastic, paper or other material) vibrations. These vibrations are transmitted to a coil, in the dynamic microphones, and are converted in an electrical voltage, some millivolts. This small voltage is the audio signal.



In the project I think use a dynamic or a condenser (electret) microphone but there are other microphones (ribbon and crystal). The choose of the microphone depend of the quality of the recorded signal and the voltage that is necessary to be amplified, because the ADC (analog-to-digital converter) only accepts -5 Volt to +5 Volt.






I have explained the working of the dynamic microphone but the condenser (electred) is different. A capacitor have two plates at some distance, we can change the capacitance changing the distance between the two plates. The sound waves vibrations change this distance and there are a relation between the capacitance and a current in the circuit, because the type of microphone is powered by a small battery (+1,5V to +9V).

Electret capsule

Electret diagram



Dynamic Microphone


Electret Microphone


References: Radio Amateur Handbook -ARRL 2000


JM Freixo Nunes 2009