Ding-Dong Doorbell. Make your Door Bell go Ding-Dong!

This doorbell electronic circuit contains only nine (9) electronic components, which includes the doorbell switch. The main Integrated Circuit (IC) is 8021-2, which already has the required internal circuitry to produce the ding-dong sound effect, each time it's pin 3 is pulled to a low state (which happens when the doorbell button is pressed).

Even though the IC 8021-2 outputs the correct doorbell sound, it's output power is so low that some amplification is required in order to drive the speaker. Accordingly, a complimentary-pair two-transistor amplifier amplifies the IC's output, which means that you can drive an 8-ohm, 500mW speaker.

During the standby period, the IC consumes nominal current of a few microamperes only. Therefore switch S1 may be kept closed. Each time switch S2 is pressed, ding dong sound is produced twice. If you try to press switch S2 a second time when the first ding dong sound is still being produed, it has no effect whatever and the two ding-dong doorbell sounds will be invariably produced.