TTL data selector
Électronique / Electronic
7400

Out last Project, TTL line selector, let you see 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 will let 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 B. But when the Select Switch is set to A, the input signal is provided by..... can you guess?

(And don't peek at the answer.)

To see how this circuit works, set the Select Switch to A when you build this Project.

When you finish, put the power ON and watch both LED 1 and LED 3. Is anything happening?

Now press the Key and see what happens to LED 1 and LED 3. Does LED 3 go on and off in step with LED 1.

Now set the Selector Switch to B. LED 3 will still go on and off.

Try pressing the Key now, does it have any effect on LED 3?

What does LED 2 do when you press the Key while the Selector Switch is at B?

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 tit most cases.