This entire circuit of beeper cum visual indicator is build and fabricated around two timer ICs and is configured in an astable multivibrator mode. The frequency generated by IC1 is controlled by capacitor C1. The output from pin 3 of IC1 is given to input pin 4 of IC2 and base of voltage amplifier transistor T1 through resistor R4. Flashing light is connected to collector of switching transistor T2 and grounded through resistor R7.
The output of IC2 is obtained from pin 3 and is given to base of power amplifier transistor T3 used to drive 8-ohm speaker connected to the collector.
NOTE: LED can be replaced with 3V to 12V DC bulb after eliminating resistor R7.
Beeper visual indicator Circuit Diagram
PARTS LIST
Resistors (all ¼-watt, ± 5% Carbon)
R1, R7 = 330 Ω
R2 = 6.8 KΩ
R3 = 5.6 KΩ
R4 = 47 KΩ
R5, R6 = 22 KΩ
Capacitors
C1 = 100 µF/10V electrolytic
C2, C4 = 0.1 µF ceramic disc
C3 = 0.01 µF ceramic disc
C5 = 1000 µF/25V electrolytic
Semiconductors
IC1, IC2 = NE555 (Timer IC)
T1 = BC148B
T2 = SK100
T3 = SL100B
Miscellaneous
SW1 = Push-To-On switch
LS1 = 8-ohm loudspeaker
LED1 = Flashing LED
