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.
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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