Basic Darkness Detector Circuit Using 555

In this tutorial, I will show you how to make a darkness detector that detects darkness using the cheapest light sensor that is LDR (Light Dependent Resistor). Darkness Detector circuits can be used in applications where the light will be going to off. 

We have also used the 555 timer IC in astable mode to generate square waves. There are some passive components that we also used a capacitor and a resistor. We have used a piezo buzzer as an alarm to indicate the darkness.

Circuit Diagram

darkness detector circuit

Components Required

  • 555 Timer IC
  • LDR (Light Dependent Resistor)
  • Piezo Buzzer
  • 10 KΩ Resistor
  • 2.2 KΩ Resistor
  • 1 MΩ Resistor
  • 1 uF/25V Electrolytic Capacitor
  • 9V Battery
  • Breadboard
  • Jumper Wires

Circuit Connection 

The 555 IC has 8 pins. Connect the pin 8 and 1 directly to 9V power supply and GND respectively. A 2.2 KΩ resistor is connected between the 9V power supply and pin 7 of 555 timer IC. Now, connect a 10 KΩ resistor between pin 7 and 6. 

Pin 6 and 2 are shorted with each other and a capacitor of 1 uF/25V is connected between pin 2 and GND. Here, the positive terminal of the capacitor is connected to pin 2 of the 555 and the negative terminal is connected to GND. 

A piezo buzzer is connected with the output pin 3 and another negative terminal is connected directly to the GND. 

The buzzer is directly connected to the output pin of the 555 timer IC.

Working of Darkness Detector

First, we will start with the 555 timers. It is configured in astable mode. When there is light falling into the LDR, its resistance becomes very low.

In this condition, the voltage divider will produce almost 0V from its output formed by 1 MΩ resistor. In this situation, the 555 timer IC will be reset. As a result, you won’t get any output from the output pin. 

When we block the LDR with an obstacle, the light falling on it will decrease. Then the resistance of the LDR will increase. This will activate the reset pin and the astable mode will activate. 

Since we connected a small buzzer to the output pin of the 555 timer IC and the buzzer will be activated. Hence, when there is enough light on the LDR, the buzzer will be off and when it is dark, the buzzer is on.

Application of Darkness Detector

This darkness detector project can be used in applications like automated switching ON-OFF light when it becomes dark.

This circuit can be a part of a home automation or security system.

Video Output

Visit our site for more awsome tutorial Electro Gadget

Leave a comment