OR gate
Électronique / Electronic

We mentioned in our last Project that digital circuits can make decisions. Here's one that decides if someone's knocking on its gates!

This Project is a very simple OR circuit. Put the power ON and set the Select Switch to B. You'll notice that LED 1 is out.

Now press the Key. What happens?

Release the Key and set the Select Switch to A. What happens now?

Leave the Select Switch at A and press the Key again. Any change?

You saw that as long as you had one of the inputs at 1, LED 1 lit (also became 1). It stayed on even when you had both inputs at 1 (Key pressed and Select Switch at A).

This is how an OR circuit works-it produces an output whenever at least one of its inputs is on (or 1, as digital electronics people like to say).

Circuits like this are sometimes called gates. It's not too hard to see where the name came from, the circuit "lets in" inputs and gives an output based upon those inputs.

The OR circuit is very handy! For example, a more complicated OR circuit could be used to turn on the lights if it got too dark in a room or if it is 7:00 p.m. Can you think of other good uses for an OR circuit? (Be sure to record what you think...)








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