Automatic street lighting controller

This automatic street light controller helps to reduce energy consumption during daylight hours.


We will need the main components:

  1. BC547 transistor – 2 pcs.
  2. 1N4007 – 1 pc.
  3. LDR (light dependent resistor) – 1 pc.
  4. Relay – 1 pc.
  5. 1K resistor – 1 pc.

The whole list looks like this:

  • BC547 -2 transistor
  • LDR (light dependent resistor)
  • Relay
  • Resistor 1k
  • 100K potentiometer
  • Power supply 12V -1
  • Connecting wires
  • Jumpers
  • Screw terminal block (2-pin or 3-pin)
  • Bread board
  • Diode 1n4007
  • AC powered
  • AC load or lamp

about the project

The main goal of this project is to switch the state of the street light from off to on and vice versa. This is done using a light dependent resistor (LDR) and a relay.

You may have seen street lights turn on and off automatically. It turns on at night and turns off during the day.

With this observation, you can notice that a certain component is used that detects day and night and turns off and on the light accordingly.

This basic function is performed using an LDR (Light Dependent Resistor). In addition to this component, various other components are used.

Great attention is paid to this project, since such automation is always needed in “smart” cities. What’s more, sometimes streetlights stay on in daylight and consume a lot of energy.

With an automatic street light controller, this energy abuse can be avoided. There is no rocket science in this project as it just consists of an LDR, a relay, resistors, a transistor, and a power supply.

Connection diagram

This circuit uses an LDR (Light Dependent Resistor) resistor. The LDR resistance changes according to the light and dark and with this resistance it is determined whether it is day or night.

Its resistance increases at night and decreases during the day. At the end of the circuit, a simple variable load (Bulb) is used, which is triggered by a relay. Two NPN BC547 transistors are used to control the relay.

Write your first C ++ game

Operating principle

When light hits the LDR, the LDR resistance decreases and Q1 turns on. But the collector is in a low state and the input signal to the second transistor Q2 is not enough to turn it on. Consequently, the relay remains off.

At nightfall, the LDR increases and the signal goes low at the base of Q1. The second transistor, Q1, receives a high signal and turns on the relay. The AC load is connected to the relay circuit, so the light comes on too.

About: Morozov Dmitry

My specialisation is software engineer. I am 35 years old and have been working in the IT field for over 15 years. I have accumulated experience in programming, project management, training and administration.