Sound machine IV
See also Sound machine I, II, III
Electronic
LM324, 74HC00

In this project, you'll use two types of sawtooth wave oscillators to make a circuit that changes sound volume and VCO frequency. You'll be hearing strange sounds.

When you finish wiring, turn power ON. Is a strange sound coming out from the speaker?

This circuit has two control volumes. First, rotate the control volume (100K). Maybe you've sensed that the sound frequency now is changing in different cycles.

Next, rotate the other control volume (50K). This time, you may have noticed that the sound volume now is changing in different cycles.

Enjoy various sounds by changing the combined operations of the two controls!

U1 A/ U1B and U1C/U1D are sawtooth wave oscillators. With either oscillator, increasing the resistance of the control volume decreases the oscillating frequency.

The sawtooth wave output of U1A is connected with a VCO consisting of NAND gates U2.

The frequency of the VCO changes in a sawtooth wave manner and the resultant sound emits from the speaker. On the other hand, the sawtooth wave output of U1D enters the emitter follower Q4, so that the speaker driving voltage changes in a sawtooth wave manner and therefore the sound volume from the speaker changes.