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How Digital Clocks Work

For any clock to work, it requires an oscillator. For a digital clock, this is generally provided by a crystal. The crystal is made from glass. When an electric charge is sent through the crystal it changes shape very slightly and creates a very slight sound. The sound is at a regular frequency which is converted to an electronic signal. The oscillations of a 60 Hertz oscillator can then be reduced to a 1 Hertz oscillation by a series of counters, the first counts one every ten oscillations and the second counts one every six counts of the 10 counter. The 1 Hertz signal is now perfectly set up to indicate the passing of seconds, because the definition of 1 Hertz is one oscillation per second!

Digital Clock Image.
The 1 Hertz oscillation is further reduced by a 10 counter in order to figure the minutes and another 6 counter added after that will give the number of hours. Each counter is then connected to a chip that converts the count on the counter to a signal to a "7-segment" display, to indicate the number counted for that particular counter. A "7-segment display" is a very familiar device that is seen on the face of most digital clocks. It can be an LED (light emitting diode) or an LCD (liquid crystal display). The "7-segment display gets its name from the fact that there are seven segments that, when all are shown, indicate the number eight. Yet when the segments are displayed selectively can show any number between 0 and 9. A string of these displays, will of course, be able to display higher numbers.

When a digital clock clicks over from 12:59 to 1:00 it has to be reset to, in effect, start over. Most digital clocks will be equipped with a built in processor looking for the number 13 in the hours column and when this occurs sets the hour counter back to 1. For a user to set the clock to the correct time, buttons are installed that allow increased frequencies to flow through the minute or hour counters, causing them to move faster.

Next Page: How Atomic Clocks Work


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