sound activated lights circuit schematic

Sound Activated Lights Circuit

This diy sound activated lights circuit turns a lamp ON for a short duration when the dog barks (or a relatively strong sound) giving an impression that the occupants have been alerted so it can be very useful.

The condenser microphone fitted in a place to monitor sound and generates AC signals, which pass through DC blocking capacitor C1 to the base of transistor BC549 (T1). Transistor T1 along with transistor T2 amplifies the sound signals and provides current pulses from the collector of T2. When sound is produced in front of the condenser mic, triac1 (BT136) fires, activates lights and the bulb (B1) glows for about two minutes.

Schematic of the sound activated lights circuit

sound activated lights circuit schematic

Assemble the circuit on a general purpose PCB (circuit board) and enclose in a plastic cabinet. Power can be derived from a 12V, 500mA step-down transformer with rectifier and smoothing capacitor. Solder the triac ensuring sufficient spacing between the pins to avoid short circuit. Fix the unit in the dog’s cage or close to the sound monitoring spot, with the lamp inside or outside as desired. Connect the microphone to the sount activated lights circuit using a short length of shielded wire. Enclose the microphone in a tube to increase its sensitivity.

Caution: Since the sound activated lights uses 230V AC, many of its points are at AC mains voltage. It could give you lethal shock if you are not careful. So if you don’t know much about working with line voltages, do not attempt to construct this circuit. We will not be responsible for any kind of resulting loss or damage.


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  • Jim Keith

    This circuit has some issues. I believe that the TRIAC gate sensitivity is the main problem. The BT136 has a typical Igt of 5mA in quadrant 1 and 30mA in quadrant 4 –and the maximum Igt is much higher, so many devices will not work –some will tend to half-wave. Find a sensitive gate device. This circuit provides a gate current of about 8mA or so.

    Another issue is that the base of T1 is biased very low (about 0.1V). Try increasing the value of R3 to 39K or 47K to increase detection sensitivity.

    Check that the mic is running in the linear range (e.g. 3 to 6V or so across the terminals) –otherwise it is wired wrong or is defective.

  • Lukwe

    Is there a way to control the frequency of the light by the frequency of the sound?

  • angela

    i am currently working this circuit .. i already tried this one in my extra pcb but unfortunately it didn’t work.. who can give me an assurance that this really work so that i can continue working this circuit. i am looking forward for any reply as fast as possible 🙂
    Thank you so much

  • fred

    I thought that this circuit is not functional. This circuit has a problem with the sensitivity to sound or noise that may come from window and put them to work even when they should not.

    • angela

      fred are you done with this circuit?? could you give me your layout?? if it is fine for you. thankyou

  • prem

    can you give brief explanation of the circuit.

  • Victor

    Am thinking of adding a siren after the light will it work?

  • shahrokh

    Dear friends i am 61 years old and like to assemble the electronic circuits its my hobby but my big problem is my languagei am iranian and i can not write so fast please help me and i can soldering very well thank you all .

  • saqib

    hey, i was wondering if different noise levels have a different voltage output?

  • Jessie

    Is the PCB layout available? If yes, can you give us the link. Thank you.

  • Patrick

    Can the Triac be compensated with a 12v relay, and secondly what is the time delay of the circuit.

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