Dark/Light Detector using 555 Timer & LDR – Electronics Mini Project

Introduction:
Here we have explained a Dark/Light Detector using 555 Timer & LDR (Light Dependent Resistor) which senses the light in surroundings and if it does not find the light, it triggers the IC and glows an LED attached with the circuit. In place of LED we can also use a buzzer or speaker to use it as dark detector alarm. The concept of this LDR circuit is quite simple and based on the working of LDR. So let’s first understand more about LDRs.
Dark/Light Detector using 555 Timer & LDR:
The electronics components required for this project are as follows:
C++

LDR

Timer
IC

Capacitors
100uF
Electrolytic
0.1uF
Ceramic

Resistors
1K
4.7K
47K

LED

9V
Power
Supply
The Circuit Diagram of Dark/Light Detector using 555 Timer & LDR is given below:
This is a simple circuit that can be assembled on a breadboard or zero PCB Board. The sensitivity of the circuit depends upon the 4.7K resistors. The resistor with a slightly lower value can make the circuit more sensitive to particular light levels.
Working of the Circuit
Let’s first understand that working LDRs are type resistors made from semiconductor materials to enable them to have their light-sensitive properties. There are many types of LDRs but one of the most popular materials used is cadmium sulfide (CdS). These LDRs or also known as photo resistors work on the principle of “Photo Conductivity”. Now what this principle says is, that whenever light falls on the surface of the LDR (in this case) the conductance of the element increases, or in other words the resistance of the LDR falls when the light falls on the surface of the LDR. This property of the decrease in resistance for the LDR is achieved because it is a property of semiconductor material used on the surface.
Here in this dark detecting LED circuit, LDR is configured with
555 timer IC
in ASTABLE mode in such a way that 555 ASTABLE generates square waves when the light intensity goes below a certain level.
Video Demonstration:
Dark/Light Detector Using 555 Timer & LDR Circuit - Electronics Mini Project
Watch this video on YouTube