Lights and Display Board Circuits

Auto Intensity Control of Street Lights

Street lights are controlled manually in olden days. These days automation of street lights has emerged. But one can observe that there is no need of high intensity in peak hours i.e. when there is no traffic and even in early mornings. By reducing the intensity in these times, energy can be saved to some extent.

There are numerous methods for conserving energy, such as turning on the street light when a car is detected, controlling street lights with LDR and relays, and so on. The suggested circuits calculate peak hours to manage street light intensity. This article shows two circuits, one describing street light control using an ATmega8 and the other showing street light control using a PIC microcontroller. The most prevalent type of street light is HID, or High Intensity Discharge, which uses a lot of energy. The circuits are constructed with high intensity LEDs instead of HID lamps to conserve electricity.


  • Auto Intensity Control of Street Lights using ATmega8
    • Circuit Principle
    • Auto Intensity Control of Street Lights Circuit Diagram
    • Circuit Components
    • Circuit Design
    • I2C Protocol
    • Simulation Video
    • How Auto Intensity Control of Street Lights Circuit Works?
    • Limitations of this Circuit
  • Auto Intensity Control of Street Lights using a PIC Microcontroller
    • Circuit Diagram
    • Components
    • Component Description
    • Working
  • Alternative Circuit
  • Auto Intensity Control of Street Lights Circuit Advantages

Auto Intensity Control of Street Lights using ATmega8

Circuit Principle

The main principle of this project is to Control the intensity of street lights using PWM.Peak hours of a particular area are calculated and accordingly PWM signal is adjusted by microcontroller to increase or decrease the intensity of street lights.

These peak hours can be calculated by considering parameters like traffic density,time, light intensity of the environment.

Auto Intensity Control of Street Lights Circuit Diagram

Street Lights

Circuit Components

  • ATmega8 micro controller
  • DS1307 IC
  • Light Dependent Resistor
  • LED array.
  • LCD display

Circuit Design

The auto intensity control of street lights circuit is simple but it requires more coding part. This circuit consists of Atmega8 controller, DS1307, LDR, Relay and LEDs.

LDR:LDR is used for calculating the light intensity of the environment .The light dependent resistor is connected to ADC1 (PC1) pin of the micro controller. The analog light value is converted to digital value using ADC.

RTC:Current time is calculated using RTC. Real time clock has 8 pins out of which SCL and SDA are connected to PC5 andPC4  pins respectively. SCL is serial clock while SDA is serial data RTC is I2C compatible, where I2C means inter integrated circuit. One bit of data is transmitted on data bus for each clock cycle.

Data can be transferred between devices, using only two bi-directional buses. Each device can act as a slave or master. The slave devices will have one address and these devices can be accessed using this address.

LCD:LCD is the display used for displaying time which is read from RTC IC. Interfacing of LCD in 4-bit mode is shown in circuit diagram. D4-D7 pins of LCD are connected to PD0-PD3 pins of microcontroller.

RS pin of LCD is connected to PD4 pin of micro controller. RW and Enable pins are connected to PD5 and PD6 pins of controller.

LED array is number of high power LEDs connected in series. It is connected to PWM pin of the microcontroller.

I2C Protocol

I2c is a communication protocol invented by Philips Company. This is well suited for communication between integrated circuits and peripherals. This uses two lines to transfer data.

  • Serial Data – SDA
  • Serial Clock – SCL.
  1. This can connect up to 128 devices using two wires. Each device connected will have an address. The device which initiates the data transfer is called Master.
  2. Every device will have 7 bit address.
  3.  Master initially sends the START bit on the data line.
  4. Then it sends the address of the device with which wants to communicate and the mode of operation i.e. read or write.
  5. The slave devices listen to the incoming data and checks if its address matches to the received data. The device whose address matches send an acknowledgement signal.
  6. Then master starts transmitting or receiving the data from the slave.
  7. After completion of the transmission, Master sends a STOP bit.
  8. Data on SDA can be changed only if SCL pin is low.

Simulation Video

How Auto Intensity Control of Street Lights Circuit Works?

  1. Initially power the circuit.
  2. Time is displayed on the LCD display.
  3. Place the LDR in darkness as the street lights switches on only when there is no light on LDR.
  4. Now check the time if the time is between 9 pm to 2 am street light glows with full intensity.
  5. From 2 pm intensity of the lights slowly starts decreasing and finally in early morning it glows with least intensity. When the light is sensed by the LDR lights are switched off automatically.

Code is written in such a way that up to 2 am lights will glow with full intensity. From then it slowly starts decreasing and finally it drops to zero in the morning.

Limitations of this Circuit

  • Even though energy is saved if there are any vehicles after fixed time, intensity of the light is low.
  • Maximum energy cannot be saved.

Auto Intensity Control of Street Lights using a PIC Microcontroller

Circuit Diagram


  • IC1 PIC 16F877A
  • IC2 DS 1307
  • LCD1 16X2 Alphanumeric LCD display
  • R1, R2 10 KΩ
  • R3, R4 1 KΩ
  • R5 10 KΩ
  • R6 1 KΩ
  • R7 10 KΩ
  • R8, R9, R10 and R11 330 Ω
  • R12 10 KΩ
  • R13 10 KΩ POT

Component Description


The microcontroller used in the circuit is a PIC16F877A. It is an 8 – bit microcontroller that reads the voltage across LDR and also checks the time in Real Time Clock IC. Based on the readings, the LEDs are switched on or off.


It is a Real Time Clock IC. The communication between microcontroller and DS1307 is via I2C protocol. It provides clock and calendar with details like seconds, minutes, hours, day, date, month and year. Time can be set in either 12 hour mode or 24 hour mode and there is an indication of AM/PM.


We utilise both LDR and RTC in the circuit because if only LDR is used, there is no way to save energy because the street lights will illuminate as soon as the intensity of light on LDR decreases, and when the intensity increases, the street lights will be switched off.

If simply RTC is utilised, the street lights will switch on and off at a predetermined time, regardless of the illumination conditions outside. RTC starts with the time set in the code when the device is turned on.

The microprocessor waits for a signal from LDR, and when the light intensity on LDR lowers, the microcontroller’s output is engaged, and the street lights begin to illuminate. Only when the c is present does this happen.

The lights continue to glow at full intensity up to 3 AM. When the time reaches 3 AM, the intensity of the street light gradually decreases and will turn off either at 6 AM or when the light on LDR in increasing, whichever is first.

Hence, the auto intensity control of street lights is achieved with the above circuit which has an LDR, an RTC, a PIC microcontroller and an LED array.

Alternative Circuit

The circuits shown above uses array of LEDs as street light in order to save power. But the same circuit can also be used to fire a normal HID street lamp. The circuit for auto intensity control of HID street light is as follows.

The above circuit shows only the interface to the street light and the rest of the circuit is same. It consists of a relay, a high intensity discharge street light that is connected to the mains supply and a diode.

The relay contact is made only when the intensity of light on the LDR is low and the street light glows.

Auto Intensity Control of Street Lights Circuit Advantages

  • Power wastage can be reduced.
  • Using LED array reduces the cost.
  • Using of RTC and LDR produces accurate results.

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