Crystal (quartz)

Gives processors an accurate clock signal.

Schematic letter: X / Y
Unit / key rating: Frequency (MHz)

Pinout

2 leads: No polarity; connects to the processor's XTAL1 and XTAL2 pins.

Real photos

What is it for?

A quartz crystal vibrates at a specific frequency when voltage is applied. Because that vibration is very stable, it's used for timing in processors, clocks and communication circuits.

The 16 MHz crystal on an Arduino Uno makes the processor take 16 million steps a second. Two small 22 pF capacitors usually sit beside it.

Things to watch out for

⚠ It can't be tested with a multimeter; a scope shows a sine-like wave on its pins.
⚠ A dropped board can crack the crystal: the processor won't run at all.

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