Sound machine II
Electronic
7476

Here's another marriage of digital and analog electronics. Take a good look at the schematic — can you guess how this circuit works even before you build it?

Make a mental note of your guess. To listen to this Project, connect the Earphone turn to ON. Can you guess what happens when you press the Key and then release it?

What happens when you press it again?

If you guessed right about how this circuit works, those two questions should be a cinch. We don't want to keep you in suspense, so press the Key and release it. Listen for a few seconds and then press and release the Key again. Now what happens?

By now you probably had no problem recognizing the multivibrator circuit. But did you notice the R-S flip-flop integrated circuit?

And, as you saw back in Project An R-S flip-flop, an R-S flip-flop "remembers."

Press the Key once, and the R-S flip-flop sets. You heard sounds in the Earphone. When you pressed the Key a second time, the sounds stopped. This was because the circuit reset. The R-S flip-flop circuit we looked at back in Project An R-S flip-flop used two transistors and other parts.

Here we use two transistors in the multivibrator circuit and an integrated circuit for the flip-flop. Does this give you any further hints about what's inside those integrated circuits? (It should!)

Have you changed your guess about what's inside an IC and how they work? If so, make a note of what you think now!