An electret is a permanently charged dielectric. It is made by heating a ceramic material, placing it in a magnetic field then allowing it to cool while still in the magnetic field. It is the electrostatic equivalent of a permanent magnet. In the electret microphone a slice of this material is used as a part of the dielectric of a capacitor in which the diaphram of a microphone forms one plate. Sound pressure moves one of its plates. The movement of the plate changes the capacitance. The electret capacitor is connected to an FET amplifier. These microphones are small, have excellent sensitivity, a wide frequency response and a very low cost.
The terminal with a solder mark(connecting to the case) is negative and the terminal without a mark is positive.
Projects the use electret microphone:
1. FM transmitter- circuit 1: This is a DIY kit. A low cost and excellent DIY kit for amateurs to begin with FM transmitter. This project uses electret microphone.
2. FM transmitter- circuit 2: This is a one transistor FM transmitter. It is a good circuit for beginners. It also uses electret microphone.
4. Clap switch DIY kit: It is an easy and low cost DIY kit for electronic beginners. This kit is available on buildcircuit.net