Sound machine III
Electronic
7400, 7476

In Project Sound machine I we saw a multivibrator circuit used with NAND gates.

Then in Project Sound machine II we found a multivibrator used with an R-S flip-flop.

What do you suppose would happen if we tried to combine these two Projects into a single circuit?

Make a quick mental note of what you suspect, because this Project will let us find out! Look at the schematic for this Project. You'll see that the NAND gates are connected to the R-S flip-flops at a point known as CK.

The output from the NAND gates control the set/reset functions of the R-S flip-flops. Notice how the output of the R-S flip-flops go to the bases of the Transistors in the multivibrator circuit.

What effect do you suppose this has upon the operation of the multivibrator?

Take care as you make the wiring connections for this Project — it's easy to make a mistake with so many connections.

Connect the Earphone and turn the power to ON.

What kind of sounds do you hear?

The strange sounds you hear are produced by the digital portion of the circuit controlling the operation of the multivibrator. You can also alter the operation of the NAND gates (and their effect on the rest of the circuit) by substituting different values of capacitors in place of the 100 µF ones.

As you might have suspected, the 100 µF capacitors control the NAND gates by charging and discharging, which turns the NAND gates on and off.

The NAND gates set or eset the R-S flip-flop, whose output then goes to the bases of the transistors, which then.....

See how everything fits together?

Like we said earlier — even complex devices are made up of a few basic circuits.