In this article, we shall learn about a simple circuit using light sensor LDR (Light Dependent Resistor).

You may be surprised to know that we can sense light and incorporate electronics in our day to day life by using very simple and easy to handle components.

Circuit description

  • The main component of this circuit is LDR. We are aware that the resistance of LDR is low when it is exposed to light. Its resistance increases when it is kept in dark. This change in resistance causes the circuit to react differently.
  • When LDR is in dark (at night), the resistance of LDR is high. This does not allow the positive supply (9V) to activate the transistor BC548. As a result, the circuit is does not work.
  • However, when LDR is in light (in morning), it resistance is low. The positive supply activates the base of transistor BC 458. It acts as pre-amplifier. Its output is given to the base of transistor BC 558.This energies the buzzer and we hear the alarm.
  • Thus, this circuit can be kept in a place in your room where the sun light falls early in the morning. When sunlight falls on LDR, it is activated and you wake up to a beautiful tune.

We will learn the ropes to build this circuit in forthcoming article.

Stay tuned for more such circuits.