How would you like to build a siren that can imitate a bird's chirping using three astable multivibrators?
All three multivibrators are made up of NAND gate CMOS ICs. Multivibrator 1 sets T1 shown in Figure 1 using the time constant of C1, C2, R3 and R4.
Multivibrator 2 sets T2 using C8 - 10 and R7, and multivibrator 3 sets T3 using C7 and R8. The circuit changes the frequency of the waves. How such circuits are called?
Why, it is FM. You can change the frequency of the generated sound at certain intervals by pressing S1 - S6. So, using various ON-OFF combinations of S1 - S6, you can produce different sounds, such as a siren sound or a bird's chirp.
Try finding the ON-OFF combination that can produce your own favorite sound.