Automatic Street Light Dimmer Circuit

In this post I will show how to construct an Arduino automatic street light dimmer circuit, which can reduce its brightness when no vehicle is passing in the road to save power.

Overview

We will be exploring the methodology of sensing the vehicle or human being without false detection which may occur due to animals and also the protocol for dimming light without wasting energy.

Street lights help the vehicles to guide along the road, but during late night hours, most of the roads will be empty and still all the street lights illuminate till morning.

Due to the illumination of street lights all night even when the road is empty, it is not worth to light the street lamps and the cost due to energy consumption  directly affect the local government.

To overcome this issue in smart way, we can reduce the brightness of the street lamps to desire level and only illuminate in full brightness when vehicles or human being pass by.

This may help the government to reduce expenditure on power and also save lot of energy which could be used for other energy demanding purposes.

The proposed idea to detect activity on the road, utilizes ultrasonic sensor which can measure the distance between the sensor and the obstacle, in this case the obstacles are vehicles or human beings.

When a vehicle comes into the range of the sensor, it does some mathematical calculations to determine the distance between the vehicles and sensor, if the vehicle is confirmed to be below the pre-determined range; the on-board microcontroller will light the street lamp at maximum brightness.

The street light will illuminate at maximum brightness for a pre-determined amount of time and reduce its brightness if no vehicles or human beings are detected further.

By now the objective of this project would have cleared. Let’s dive into circuitry of the proposed setup.

Circuit Operation

The automatic street light dimmer circuit consist of Arduino which is the brain of the project, an ultrasonic sensor for detecting vehicles or human beings. A 9V regulator is provided for powering the arduino microcontroller board and a MOSFET for driving the LEDs which consumes few amperes at peak brightness.

The LED module and power supply for the setup must be selected carefully so that there will be adequate power available for the whole circuit and does not overload the power supply.

The LED module can be homemade one which is shown in schematic or may be purchased for market, but before constructing or getting one form market make sure to calculate the voltage and current requirements for the power supply.

The power supply may be an SMPS or constructed using transformer, rectifier and voltage regulator.

The LED reduces its brightness by using PWM. The PWM is square wave, it turns on and off supply to LED rapidly with well determined on and off width in a single cycle. The width of the on and off time determine the brightness of the LED.

When the street light switches to full brightness the supply to LED will have no pulses and steady DC will be supplied.

The whole setup can be implemented as shown below:

Setup Diagram

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The ultrasonic sensor is elevated around 3.5ft to 4ft above the ground; this is done so that it only detects vehicles and human beings, since their average height is around the same and when dogs or cats or any other animals which usually roam around the city will not trigger the street light to maximum brightness.

The animals which live and roam around the city are below 3.5ft tall.

The sensor height may be adjusted to operate at optimum level as described in the above picture.

The threshold distance can be controlled in the program.

When the Arduino detects the obstacle detected below pre-determined distance the LED lights go peak brightness.

Program Code:

//-------------------- Program developed by R. Girish --------------------//

// Ultrasonic sensor connections
const int trigger = A1;     // Trigger pin of ultrasonic sensor
const int echo    = A2;     // Echo pin of ultrasonic sensor

// Power pins for ultrasonic sensor (provided through Arduino)
int vcc = A0;              // VCC pin for sensor
int gnd = A3;              // GND pin for sensor

// Output load
int LED = 3;               // PWM pin connected to LED or lamp driver

// Variables used for distance calculation
long Time;                 // Stores echo pulse duration
float distanceCM;          // Raw distance in cm
float distanceM;           // Raw distance in meters

// User settings
float distance = 100;      // Threshold distance in cm
int dim    = 28;           // Minimum brightness level
int bright = 255;          // Maximum brightness level

// Final calculated values
float resultCM;
float resultM;

void setup()
{
  // Configure I/O pins
  pinMode(LED, OUTPUT);
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(vcc, OUTPUT);
  pinMode(gnd, OUTPUT);

  // Start serial communication for monitoring
  Serial.begin(9600);
}

void loop()
{
  // Powering the ultrasonic sensor
  digitalWrite(vcc, HIGH);
  digitalWrite(gnd, LOW);

  // Ensure trigger pin is LOW before sending pulse
  digitalWrite(trigger, LOW);
  delay(1);

  // Send 10µs trigger pulse
  digitalWrite(trigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigger, LOW);

  // Measure echo pulse width
  Time = pulseIn(echo, HIGH);

  // Convert time into distance
  distanceCM = Time * 0.034;   // Speed of sound calculation
  resultCM   = distanceCM / 2;
  resultM    = resultCM / 100;

  // Display distance values on Serial Monitor
  Serial.print("Distance in cm: ");
  Serial.println(resultCM);

  Serial.print("Distance in meter: ");
  Serial.println(resultM);

  Serial.println("------------------------------------------");

  // If object is within the threshold distance
  if (resultCM <= distance)
  {
    analogWrite(LED, bright);  // Full brightness
    delay(10000);              // Hold ON for 10 seconds
  }

  // If object is beyond the threshold distance
  if (resultCM >= distance)
  {
    analogWrite(LED, dim);     // Dim brightness
  }

  delay(100);                  // Small delay for stability
}

//-------------------- Program developed by R. Girish --------------------//

NOTE:

• The threshold distance can be adjusted by replacing the Value with your own.

float distance = 100; // set threshold distance in cm

The value must be entered in centimetre; the maximum value can be 400 to 500 cm or 4 to 5 meter.

• The dimming of the light can be adjusted by using

int dim = 28; // adjust minimum brightness

255 is maximum brightness 0 is lights off.

We can also witness the distance between the sensor and the obstacle in serial monitor.

Upgrading the Code for Enabling Automatic Day, Night ON/OFF of the Lamp

Program Code

//-------------------- Program developed by homemade-circuits.com --------------------//

// Ultrasonic sensor connections
const int trigger = A1;     // Trigger pin of ultrasonic sensor
const int echo    = A2;     // Echo pin of ultrasonic sensor

// Power pins for ultrasonic sensor
int vcc = A0;              // VCC pin for sensor
int gnd = A3;              // GND pin for sensor

// LDR connection
int LDR = A4;              // LDR connected to analog pin A4

// Output load
int LED = 3;               // PWM pin connected to LED or lamp driver

// Variables used for distance calculation
long Time;                 
float distanceCM;

// User settings
float distance = 100;      // Detection distance in cm
int dim    = 28;           // Dim brightness
int bright = 255;          // Full brightness

// LDR setting (must be calibrated using Serial Monitor)
int LDR_threshold = 73;

// Final calculated value
float resultCM;

void setup()
{
  pinMode(LED, OUTPUT);
  pinMode(trigger, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(vcc, OUTPUT);
  pinMode(gnd, OUTPUT);

  Serial.begin(9600);
}

void loop()
{
  // Read LDR value
  int LDR_value = analogRead(LDR);

  Serial.print("LDR Value: ");
  Serial.println(LDR_value);

  // -------- DAY TIME CONDITION --------
  if (LDR_value > LDR_threshold)
  {
    analogWrite(LED, 0);        // Light OFF during daytime
    delay(500);
    return;                     // Skip ultrasonic sensing
  }

  // -------- NIGHT TIME CONDITION --------
  digitalWrite(vcc, HIGH);
  digitalWrite(gnd, LOW);

  // Trigger ultrasonic pulse
  digitalWrite(trigger, LOW);
  delayMicroseconds(2);
  digitalWrite(trigger, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigger, LOW);

  // Measure echo pulse
  Time = pulseIn(echo, HIGH, 25000);   // Timeout added for stability

  // Convert time to distance
  distanceCM = Time * 0.034;
  resultCM   = distanceCM / 2;

  Serial.print("Distance in cm: ");
  Serial.println(resultCM);
  Serial.println("--------------------------------");

  // -------- OBJECT DETECTED --------
  if (resultCM > 0 && resultCM <= distance)
  {
    analogWrite(LED, bright);   // Full brightness
    delay(10000);               // Light ON time
    analogWrite(LED, 0);        // Turn OFF after delay
    return;                     // Restart loop
  }

  // -------- NO OBJECT DETECTED --------
  analogWrite(LED, dim);        // Dim light during night

  delay(200);
}

//-------------------- Program developed by homemade-circuits.com --------------------//

LDR cannot be connected directly to Arduino alone, it must be used with one fixed resistor, so voltage divider is formed, otherwise reading will not work.

Components Needed

• 1 × LDR
• 1 × fixed resistor (10k is ideal, anything from 10k to 47k works)

Step By Step Wiring

Take one lead of the LDR. Connect it directly to +5V of the Arduino.

Then, take second lead of the LDR and connect it to analog pin A4 of the Arduino.

Connect the fixed resistor (10k). One end of resistor goes to A4, the same point where LDR second lead is connected. Other end of resistor goes to GND of the Arduino.

That is it….

Now A4 remains connected between LDR and resistor and senses light level, so reading changes.

How This Works Electrically

During daytime, or bright light, LDR resistance becomes low. Then voltage at A4 goes high, and so Arduino reads large analog value.

During night time, or darkness, the LDR resistance becomes high, then voltage at A4 goes low. so Arduino reads small analog value.

Code Logic Matching

If LDR_value > threshold… then Day is detected, and then Lamp is turned OFF.

If LDR_value < threshold…. then Night is detected, then Lamp is turned ON and is ACTIVE.

Practical Tip

After wiring, please upload the code, then open Serial Monitor and note LDR readings for the following:

• Bright sunlight
• Indoor light
• Complete darkness

Next, set the following line in the Arduino code accordingly:

int LDR_threshold = (day_value + night_value) / 2;

If you have any further questions regarding this Arduino based automatic street light dimmer circuit feel free to ask in comment section.