Light Screamer Circuit Using LDR and 555 Timer IC

A tutorial on how to make a light screamer circuit using LDR (Light Dependent Resistor) and 555 timer IC. This circuit generates a screaming noise depending on the amount of light incident on the LDR/Photocell.

There will be no sound from the circuit (Almost) when it is completely dark, and as the brightness of light incident on the LDR increases, the intensity of sound starts increasing gradually.

Watch the video above for detailed step by step instructions on how to build this circuit. Explanation of how the circuit works is also included in the video.

Components Required:

  • 555 IC
  • Light Dependent Resistor (LDR / Photocell)
  • 8 Ohm Speaker
  • Capacitors: 100nF, 10uF
  • Resistor: 1K
  • Breadboard
  • Few Breadboard Connectors
  • (5-9)V of DC Power Supply

Circuit Diagram:

Schematic of Light Screamer Circuit using LDR and 555 IC

Working of the Circuit:

[You may first go through the explanation provided in the video tutorial for better visual understanding]

Basics of LDR: LDR stands for Light Dependent Resistor. As its name indicates, the resistance between both its terminals depends on the amount of light incident on it. More the amount of light, lesser will be the resistance, and vice versa.

In the previous tutorial (Flashing/Blinking LED Circuit) we have practically observed that increasing the value of resistor R1 (The resistor through which the capacitor charges and discharges) will increase the output frequency. Similarly decreasing its value decreases the output frequency because the capacitor will now be able to charge and discharge very quick.

In this circuit, we allow the capacitor to charge and discharge via the output pin. And we used an LDR in series with a 1K resistor between the capacitor and the output pin (Pin-3). So as the light incident on the LDR increases, its resistance reduces and so the capacitor will be able to charge and discharge quickly. As a result, the output frequency increases and this causes the speaker to produce loud sound (High Pitch).

Similarly, as the light incident on LDR reduces, its resistance increases and so the capacitor takes more time to charge and discharge. As a result, the output frequency reduces and this causes the speaker to produce sound with less intensity (Low Pitch).

If you have any queries/suggestions, feel free to post them in the comments section of this video: Light Screamer Circuit Using LDR