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Power Supply Resumption Alarm

Here is an audio annunciator which can be useful in factories, industries, auditoriums, and theatres etc where generator is used when power fails. It produces an alarm for a predetermined time when power resumes.

power supply resumption alarm

The circuit is built around IC555 wired in monistable mode. The surge when power resumes triggers the monostable which switches transistor SL100 on. The relay energized and the bell or buzzer connected to N/O contacts of the relay operates. The preset time depends upon VR1 and C2. The Capacitor C3 connected to pin 2 of 555 should have low leakage.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R1, R2 = 10 KΩ

R3 = 470 Ω

VR1 = 1 MΩ (DELAY ADJ.)

Capacitors

C1 = 1000 µF/25V

C2 = 100 µF/25V

C3 = 1 µF/25V

C4 = 0.01 µF

Semiconductors

IC1 = NE555

T1 = SL100

D1 – D3 = 1N4001

Miscellaneous

X1 = 12V – 0 – 12V 500 mA secondary

F1 = Fuse

RL1 = 12V, 400Ω relay

230V buzzer

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