 The Electret Microphone, another component concealing its inner workings within a sturdy metal case. Let's see what makes it go. At the heart of it all, hiding under a metal plate, is a through-hole JFET transistor. It acts as a sensitive amplifier with its source pin connected to ground. A PCB trace connects ground to the housing, which then connects to a conductive layer attached to this disc of Electret film. The transistor's gate pin connects to a conductive plate below, separated from the Electret film by a small gap. Together, the plate and film form a simple capacitor. Moving air, aka sound, stretches the film slightly, bringing it closer to the plate, effectively increasing the value of the capacitor. The transistor responds by varying the current between its drain and source pins, which we can detect with a microcontroller.