C-MOS data selector
Electronic
74HC00

In our last project (C-MOS line selector) you saw how data could be sent to two or more different outputs. You can probably think of some situations where we might want to (or need to) do the opposite - send data from two or more different sources to one output. This circuit lets us see how this can be done.

When you look at the schematic for this project, you'll notice two different input sources. One is provided by the multivibrator circuit when the select switch is set to the down position. But when the select switch is set to the up position, the input signal is provided by.....can you guess? (And don't peek at the answer.) Yourself!

You provide the input signal by pressing and releasing S1. To see how this circuit works, set the select switch up when you build this project and watch both LED 1 and LED 3. Is anything happening?

Now press S1 and see what happens to LED 1 and LED 3. Does LED 3 go on in step with LED 1 ?

Now set the select switch down. LED 3 start to go on and off in step with LED 2. Try pressing S1 now - does it have any effect on LED 3? What does LED 3 do when you press S1 while the selector switch is down?

More complex versions of these circuits are found in computers and other highly advanced digital circuits. And - as you probably suspect - switching from one input channel to another is done electronically in most cases.