# Eli5: how do quartz powered watches work?

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how do quartz powered watches work?

In: Engineering

They have a tiny, very precise, electrically powered tuning fork inside. It vibrates 32768 times per second, which is too high to hear. This tuning fork is much more accurate than any previous mechanical timing devices.

Why 32768? Because dividing by two is a very simple thing to do electronically, and if you cascade a bunch of divide-by-two circuits, you get 16384-8192-4096-2048-1024-512-256-128-64-32-16-8-4-2-1. Then you pipe the “1” pulse to a motor that ticks the second hand in an analog watch, or to a digital counter than counts seconds, minutes and hours in a digital watch.

basically, when you run electrical current though a quartz crystal, it vibrates at *exactly* 32,768 times a second.

so, you run a current though it, then count the vibrations. Every 32,768 vibes, you increment a second.

Quartz is a special type of material. It’s a crystal that changes shape when you put an electric current though it, and generates an electric current when you change its shape.

What they do in a watch is they use it like a tuning fork. When you hit a tuning fork it vibrates at a very specific frequency. So they “hit” the tiny quartz crystal inside the watch with some electricity then “listen” to it vibrating by the electricity it products.

Because it is vibrating at a specific frequency they can count the vibrations. Most watches have crystals tuned to 32768 Hz, so when they have counted 332768 vibrations it means exactly 1 second has passed.

They don’t *power* the watch, you’d still need something like a battery for that, they are the “mechanism” for the clock, bridging the gap between of fuck-tons of tiny gears and then computer chips.

In a nutshell what they do is receive electricity from a battery which makes the quartz change shape. This is why quartz is special, it changes shape with electricity AND does so really regularly. So if they cut exactly the same piece of quartz shape and give it the same energy they know exactly how it’ll change shape, like, perfectly.

Now do stuff with the electricity to make the electricity pulse, this makes the quartz pulse and do this really fast, suddenly your quartz is like a drumstick on a snare drum. Tappity-tappity-tappity in perfect, constant beat forever.

Now you just tell the motors that control the hands of you watch, “count the tappitys”, on every 10th tappity you increment the second hand forward one, on the 600th increment the minute hand.. etc. etc.

In a nut shell the quartz is just the world’s best drummer keeping the world’s tightest groove from the motors in the watch. But it’s not 10 tappitys because that would put it in the range of human hearing, it’s more like 40,000 tappitys per second.

They aren’t powered by quartz, they use a standard battery like any other watch.

The Quartz crystal is used to measure the second. Quartz crystals in watches are designed to oscillate at a highly predictable rate, so ~32768 oscillations of that crystal is equal to 1 second.

Quartz has a piezoelectric effect, when it moves it releases electricity, and when electricity is applied it moves.

So when a potential difference is applied, it moves, when it returns to its original shape a short, but consistent time later, it gives back a potential difference. We use this to create a system that oscillates with a set frequency, often a few kilohertz. And then we count the number of oscillations and tick the watch after every few thousand ticks.

You know how a tuning fork always produces a very specific note? That’s because the shape of the tuning fork is precisely adjusted to vibrate at the frequency corresponding to that note.

Quartz is a piezoelectric material. That means it generates electricity when you bend it, and bends when you apply electricity to it.

Now put those things together: by [cutting a small chunk of quartz into a tuning fork shape](https://en.m.wikipedia.org/wiki/Quartz_clock#/media/File%3AInside_QuartzCrystal-Tuningfork.jpg), you get something that vibrates at a specific frequency. By passing an electrical current through the tuning fork, the piezoelectric effect keeps it vibrating “forever”. When you initially put the battery in, a little burst of electricity from the circuit closing gives the initial kick that starts the quartz vibrating.