Beeper and visual indicator

Here is a circuit of simple, inexpensive and very useful project beeper and visual indicator, used to visual indicator lights up with each beep having the same time period.

alarm project using 555 timer IC

Circuit description of beeper and visual indicator

This entire circuit of beeper and 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.


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


C1 = 100 µF/10V electrolytic

C2, C4 = 0.1 µF ceramic disc

C3 = 0.01 µF ceramic disc

C5 = 1000 µF/25V electrolytic


IC1, IC2 = NE555 (Timer IC)

T1 = BC148B Replacements: BC141 , BC140, 2N2222

T2 = = SK100 Replacements: BEL100 , 2N5401, BC177 If using replacement proper management for heat dissipation is advised.

T3 = SL100B Replacements: 2N4922 , 2N4921,2N4238, FCX1053A


SW1 = Push-To-On switch

LS1 = 8-ohm loudspeaker

LED1 = Flashing LED


Related Project

  1. 2-tone-door-bell Generated a ding-dong sound similar to an electrical bell
  2. Flasher with Beeper It can be used as flasher beeper in scooter, motorcycle
  3. Man Machine Sound Generator produced different type of man as well as machine sound
  4. Multi Sound Generator use 3V DC battery to operate instead of AC mains, with good quality sound.

10 thoughts on “Beeper and visual indicator”

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  4. T1 = BC148B
    T2 = SK100
    T3 = SL100B

    I can’t find any of those in our place. Is there any substitutes that can be plugged in instead of these transistors? Thank 🙂 I would like to try this circuit.

    1. You can use any general purpose NPN transistor or Audio frequency transistor in place of T3 (SL 100) but proper arrangement should be done to dissipate the heat produced for eg. you can use heat sink and you should make sure that the transistor used can withstand at least around 500-1500 mili-amps of current.

  5. if that’s the case, i’ll just use another 2N2222. 🙂 its a general purpose transistor. thanks admin 🙂

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