TTL latch circuit
Électronique / Electronic
7400, 7476

This is another circuit whose name describes how it works so make a guess before building this Project and finding out for sure.

As you build this Project, set the Select Switch to A. When you finish the wiring connections, turn the power ON and press the Key.

You'll see LED 1 light up. Now switch the Select Switch back and forth from A to B. What does LED 1 do?

Now set the Select Switch to B and press the Key again. You'll see that LED 1 goes out.

Move the Select Switch from B to A and back again. Is there any change in LED 1 ?

You can easily see where the latch circuit gets its name. The circuit can "latch" in a certain condition and keep the same output regardless of changes in the input.

We can use latch circuits to control the operations of electronic devices since it will maintain a certain output until we send a signal to cause a change, we don't have to keep sending an input signal to the latch circuit continuously. This means just a touch can activate a latch circuit ... just as you saw in this Project,