2 – Tone Door Bell

2 – Tone Door Bell

Here is a circuit of simple 2 – tone door bell, generates ding-dong sound similar to an electrical bell.

Circuit Description of 2 - tone door bell

The 2 – tone door bell circuit is designed and fabricated around IC CD40106 hex schmittriger inverter. To prevent false triggering R-C filter network is connected to switch SW1. IC1 is configured as astable multivibrator. It generates two frequency 600 Hz and 400 Hz each for 0.5 seconds. Thus at first speaker receives 600 Hz frequency for the period 0.5 seconds followed immediately by 0.5 second of 400 Hz frequency.

Capacitors C6 and C7 is used in this door bell to determine the tone frequency and is varied as these mostly discharged via R6 (Parallel connected) resistor in approximate 2 seconds before the circuit can be re-triggered.

circuit diagram of door bell


Resistors (all ¼-watt, ± 5% Carbon)

R1, R2, R8, R10 = 4.7 KΩ

R3, R4, R5, R6, R7, R9 = 10 MΩ

R11 = 33 Ω


C1 = 0.001 µF

C2 = 0.22 µF

C3, C4 = 0.047 µF

C5 = 100 µF/16V

C6 = 120 pF

C7 = 150 pF

C8 = 10 µF/16V


IC1 = CD40106

D1 – D5 = 1N4148

T1 = SK100


SW1 = Push to on switch

LS1 = 8 Ω

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