Why Clocks Use This Tiny Crystal

Run a clock on an MCU's internal RC oscillator alone, and depending on the part it can drift by tens of minutes a day. That's why timekeeping circuits use a tiny quartz crystal. Inside the can is a piece of quartz cut like a tuning fork. Quartz is piezoelectric: a voltage bends it slightly, and bending it makes a voltage. Kept driven by the circuit, it vibrates very steadily at a frequency set by its shape and size. A watch crystal vibrates 32,768 times a second. That's 2 to the 15th power, so halving it 15 times gives exactly one tick per second. Crystals still have tolerance, often ±20ppm at room temperature, which is up to about 1.7 seconds a day. And the capacitors on both sides must match the load capacitance in the crystal's datasheet, or it won't run at exactly 32,768 Hz. #Electronics #Embedded #Crystal #Shorts