The main part of this doorbell circuit are two NE555 timer ICs.When some one presses switch S1 momentarily, the loud speaker sounds a bell tone as long as the time period of the monostable multivibrator built around IC1.
When the switch S1 pressed, IC1 is triggered at its pin 2 and output pin 3 goes high for a time period previously set by the values of POT R4 and POT R5.When the output ofIC1 goes high it resets IC2 and it starts to oscillate to make a bell sound through the speaker.The IC2 is configured as an astable multivibrator whose oscillation frequency can be varied with the help of POT R5.By adjusting the values of R4 & R5, modifications on the tone are possible.
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Circuit diagram with Parts list.
- The circuit has to assembled on a good quality PCB or common board.
- The IC1 & IC2 has to be mounted on IC holders.
- Power the circuit from a 9V battery or 9V DC power supply.
- Switch S1 is push button switch.