Digital sine wave generator
555, 74HC191, 74HC4028, 7476, 7400
Oscillateurs   /    Oscillators
Électronique / Electronic

In this project, you're going to make a sine wave using digital technology. Take a look at the schematic. The circuit consists of an oscillator, counter, decoder, and a resistor network. The resistance values in the resistor network are different from one another. Given these hints, try to guess how you can generate a sine wave digitally.

Anyway, finish wiring and turn power ON. You'll hear a monotone from the speaker.

U1 555 is an oscillator, and the counter U2 counts up with the pulses from U1.

The outputs QA - QC of the counter U2 are decoded by the decoder U4.

As the counter U2 counts up, the output Q9 of the decoder U4 changes to H, when the RS flip-flop U3 is reset to switch the counter U2 to count-down mode.

The count-down proceeds until the output Q0 of the decoder U4 goes H, when U3 is set and U2 switches back to count-up. In this way, the counter shifts back and forth in the range of values 0 - 9.

In the meantime, the outputs Q0 - Q9 of the decoder U4 change to H one after another. Therefore, the voltage divided by the resistors connected to Q0 -Q9 and by R13 come to have 10 different voltage values as shown in Figure 1, so that the oscillating tone of this waveform is emitted from the speaker.