How do digital devices know exactly how long a second is?
In: Technology
You use a crystal oszillator. Basically if you provide a quartz crystal with power it oscillates with a given frequency depending on its shape. With a given frequency depending you only have to count how many times you had a high or low and you know after x high 1 second passed.
They have analog circuits that measure time. One of the simplest ways is to wait for a capacitor to charge up through a resistor, but it’s not accurate as each device might have a slightly different amount of capacitance and resistance. The most common way is to use a tiny vibrating quartz crystal, since they can be manufactured with very accurate vibration rates. For even more accuracy, you can wrap a heater around the quartz crystal so it always stays at the same temperature and doesn’t thermally expand. Most devices don’t bother with that. For crazy accuracy, you can plug in an atomic clock.
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