Sound out timer
Electronic
7400, 7476

Look closely at the schematic for this Project — notice anything familiar about it?

This circuit uses a divide by 4 counter. That should give you a BIG hint how this circuit works before you build it!

Turn the power to ON when you finish the wiring connections. You'll hear a sound from the Speaker.

Now press and release the Key. The sound from the Speaker will stop ... only to resume a short time later!

You can easily spot the astable multivibrator in this Project. You may have also spotted the multivibrator made up of NAND gates (if you didn't, take at look back at TTL astable multivibrator).

Have any idea how these two multivibrators help this circuit operate?

Here's a hint: when the Q output of both J-K flip-flops is 1, the NAND multivibrator stops working. And you can also see that the Q outputs of both J-K flip-flops also lead back to the transistor multivibrator through a couple of NAND gates.

Try using just one 100 µF capacitor in the NAND multivibrator circuit. What effect does this have on circuit operation?

Did you expect this to happen?