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How DO you make a digital clock?

Hosted by: Michael Aranda
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(SciShow Intro Plays)

Michael: Do it yourself electronics, particularly digital clocks, have been in the news this week, and there are a lot of things to talk about with this story and from Tumblr to the White House, people are talking about them, but we here at SciShow are interested in how digital clocks actually work.

Well, first you need a power source, and that's either a battery or a wire running into the wall. Most consumer digital clocks use an ordinary plug with a transformer that steps down the power supply before the current runs into the clock. Plus, there can be a connection for 9 volt batteries or a backup power source.

Next, a clock needs a heartbeat, some way if counting regular intervals in order to keep time. In a traditional pendulum clock, the heartbeat comes from the swinging of the pendulum, but in a digital clock, this heartbeat can be generated electronically in a couple different ways. It might use a crystal oscillator for example, a piece of quartz that vibrates at a regular frequency when it's attached to an electrical current.

Or it might use a circuit that counts the oscillations of the electricity coming through the wire. These oscillations are measured in cycles per second using units called hertz. So if your clock runs at 60 hertz, the electricity being fed to it is oscillating 60 times per second. Those oscillations are just the regular built-in fluctuations in the amount of electricity being fed into electronics. A digital clock counts those oscillations to keep time.

The third thing you need in a clock is a way to split up that heartbeat into different units of time. In a mechanical clock, that's done with gears. A different set of gears connects the pendulum to the hour hand, the minute hand, and the second hand, so that each move a different specific amount as it swings.

Digital clocks don't have gears of course, instead they have a chip that counts the heartbeats then acts like a simple calculator to divide the number of heartbeats into conventional units of time. So if you have a unit that pulses 60 times every second, the chip counts the oscillations, and for ever 60 it records that as one second having passed. For every 3,600 oscillations, it records a minute, for every 216,000, that's an hour.

Now, the last thing you need for your clock is a display, like an LED screen, with a separate circuit that lets it communicate with the counters. That circuit is running its own simple program that tells the screen what to display based on how much time has passed. When the second counter reaches 10 for example, the program says "put a 1 and a 0 in these specific places" and after the counter reaches 59, it cycles back to 0.

And that's all you really need: a power source, a heartbeat, a counter that can divide up the heartbeat into longer measurements of time, and a display screen with its own circuit that tells it what to do with the numbers generated by the counter. In the world of modern technology, surprisingly simple.

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