Audio Circuit Diagrams

Screaming Siren Circuit

A siren is a gadget that emits a loud sound. They serve as a medium of communication. Emergency vehicles, such as police cars, ambulances, and fire engines, all have sirens. Sirens are typically used as a signal or warning. Different circuits are used to create different sirens. This post will show you how to make a screaming siren lights circuit. Screaming siren lights emit a siren in response to the amount of light falling on the circuit. It’s also known as a Light-Activated Alarm System.


  • Screaming Siren Lights Circuit Principle:
  • Screaming Siren Lights Circuit Diagram:
    • Screaming Siren Lights Circuit Description:
    • Screaming Siren Lights Circuit Simulation Video:
    • How to Operate this Light Activated Alarm Circuit?
    • Screaming Siren Lights Circuit Applications:
      • Limitations of the Circuit: 
    • Checkout this project output video

Screaming Siren Lights Circuit Principle:

The primary premise of this circuit is to generate sound based on the amount of light falling on it. As the amount of light falling on the circuit grows, it produces longer pulses, which produces more sound. The 555 timer IC is the circuit’s main component. This causes oscillations in the Light Dependent Resistor, which are dependent on the light intensity.

Screaming Siren Lights Circuit Diagram:

Screaming Siren Circuit

Screaming Siren Circuit Diagram

Circuit Components:

  • 555 timer IC
  • Light Dependent Resistor
  • Speaker
  • Capacitors C1,C2
  • Resistor R1
  • Breadboard
  • Connecting wires.
  • DC battery.

Screaming Siren Lights Circuit Description:

The 555 timer IC is the heart of this light-activated alarm circuit. It’s mostly utilised for timing purposes. It generates the required oscillations. This can be used in three different ways. Monostable mode, Astable mode, and Bistable mode are the three modes. It is in the astable mode in this circuit. There is no need for external triggering in this mode. The sixth pin of the IC is connected to the second pin of the IC. The fourth pin is connected to the eighth pin and is powered by a 5V supply. A capacitor C1 connects the third pin to the speaker.

The second pin attached to the sixth pin continuously triggers the circuit in astable mode. As soon as the 5v supply voltage is connected to the VCC, the capacitor C2 begins to charge through both the LDR and R1 resistors. The output pin 3 activates when the capacitor hits 2/3 of VCC, and the capacitor begins to discharge through R1. As a result, pulses are produced at the output. When the capacitor reaches 1/3rd of VCC, it begins to charge again.

For altering the sound in the circuit, the circuit mostly relies on the light dependent resistor. Photo resistors are another name for them. In general, light-dependent resistors have a high resistance in the dark and a lower resistance when lit with light. The photo resistors employed here are two mega ohm resistors, which means their resistance in darkness is in the mega ohm region. Two resistors, LDR and a 1K ohm resistor, are connected in series in this circuit. These are connected to the 100nf capacitor C2. Sixth and second pins are both shorted and linked to the same capacitor C2.The ground is linked to the capacitor’s other end. Another important component in the circuit is the speaker. It interprets electrical signals and converts them to physical signals. This performs the function of a transducer. A permanent magnet and a moving magnet will be found inside the speaker. Using these magnets, the electrical signals from the 555 timer IC are turned into vibrations. At output, these vibrations can be heard. In this case, theA speaker with an impedance of 8 ohms was employed. This should be connected to the 555 timer IC’s output pin 3 through an electrolytic capacitor C1. The capacitor’s positive terminal is linked to the timer’s Pin 3 and its negative terminal to the speaker’s positive terminal. The negative terminal is connected to the earth.

Screaming Siren Lights Circuit Simulation Video:

How to Operate this Light Activated Alarm Circuit?

  • As shown in the circuit diagram, connect the circuit on the breadboard.
  • Connect the 5V supply voltage to the circuit now.
  • To begin, place the LDR in the dark.
  • The output no longer produces any sound.
  • Place the LDR in the light now. Gradually increase the amount of light falling on the LDR.
  • The increase in sound created can be seen as the intensity of the light gradually increases.
  • Now turn off the power.

Screaming Siren Lights Circuit Applications:

  • This circuit can be utilised in civil defence sirens to provide notice when natural disasters strike.
  • This can be used as a signal in an emergency.

Limitations of the Circuit:

  • This circuit is tested theoretically, to implement practically it may require changes.


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