Fuse and Power Failure Indicator

Fuse blowing is common problem, but is so tedious to go and check because every time it may not blown. Here is a simple circuit of fuse and power failure indictor,for indicate the power failure by giving alarm. The logic of this circuit is so simple and it also overcome the problem of checking every time.

Circuit Description of fuse and power failure indicator

The entire circuit of fuse and power failure indicator is build and fabricated around LDR, timer IC and LED. Here LED get power-supply from AC source which is stepped down by transformer X1 and further rectified by diode and changed to regulated 6V D.C. with the help of regulator IC 7806 (IC1). Here LED1 and LDR1 are kept in a cabinet together. Transistor T1 and T2 is used as cascade amplifier which amplify the divided voltage from LDR1. Trigger is given to pin no 2 of IC2 from the collector of T2. Here timer IC (IC2) configured as monostable multivibrator and its output is given to reset pin 4 of IC3 which is configured as astable multivibrator. The high output is given for about 7 second from IC2 to IC3. IC3 generate audio frequency and connected to loudspeaker. An alarm sound is produced from fuse and power failure indicator, indicating the power failure.



Resistors (all ¼-watt, ± 5% Carbon)

R1 = 100 Ω

R2, R4, R6 = 10 KΩ

R3, R5 = 1.5 KΩ

R7 R8 = 1 KΩ

VR1 = 10 KΩ

VR2 = 100 KΩ

VR3 = 1 KΩ


C1 = 1000 µF/25V

C2, C4, C6 = 0.01 µF

C3 = 100 µF/16V

C5 = 0.47 µF

C7 = 33 µF/16V

C8 = 0.47 µF


IC1 = 7806 (regulator IC)

IC­2, IC3 = NE555 (Timer IC)

D1 = 1N4001


X1 = 230V AC primary to 9V-0-9V, 250mA secondary transformer

LED1 = White

F1 = Fuse 500 mA

S1 = ON/OFF Switch

S2 = Push-to-on switch

Batt1 = 6V Battery

LS1 = 8Ω, 0.5W Speaker


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