Crystal oscillator

A crystal oscillator is a timekeeper for electronics. At its heart is a thin slice of quartz that rings at one very exact frequency, like a tuning fork, and the circuit around it turns that ringing into a steady clock signal.

It works because quartz is piezoelectric: squeeze it and it makes a voltage, apply a voltage and it bends. To build one, a quartz crystal, usually grown in a factory, is sawn at a carefully chosen angle into wafers, then cut into tiny blanks. The thickness of a blank sets its frequency, so it is lapped very precisely. Thin silver electrodes are deposited on both faces, and the blank is mounted inside a small aluminum oxide ceramic package, fine-tuned and sealed under a metal lid.

On the main board, crystals give the chips the beat everything else counts from, often a few tens of megahertz. In the Wi-Fi and Bluetooth module, the crystal keeps the radio exactly on its channel. Many boards use just the quartz part, a crystal resonator, with the rest of the oscillator circuit built into the chip it feeds. Quartz watches use the same idea at 32,768 vibrations per second.