Arduino Photoresistor Circuit Tutorial

In this tutorial, you will learn how to create a simple light-detecting circuit using a photoresistor (LDR) and an Arduino Uno Mini. The circuit will allow your Arduino to detect light in its surroundings.

Components Needed

• Arduino Uno Mini (any Arduino board will work)
• Photoresistor (LDR)
• 10kΩ resistor
• Breadboard
• Jumper wires

Circuit Diagram

Step-by-Step Instructions

1. Connect all of the Components

1. Connect one leg of the photoresistor to the 5V pin of the Arduino.
2. Connect the other leg of the photoresistor to:
   • Analog pin A0 of the Arduino
   • One leg of the 10kΩ resistor
3. Connect the other leg of the 10kΩ resistor to the GND pin of the Arduino.

This creates a voltage divider circuit where the voltage at A0 will change based on the light level.

2. Understanding the Circuit

The photoresistor changes its resistance based on light intensity:

• Bright light = lower resistance (about 1kΩ)
• Darkness = higher resistance (can be several hundred kΩ)

The 10kΩ resistor forms a voltage divider with the photoresistor:

• In bright light, the voltage at A0 will be higher (closer to 5V)
• In darkness, the voltage at A0 will be lower (closer to 0V)

3. Upload the Arduino Code

// Define the analog pin for the photoresistor
const int ldrPin = A0;

void setup() {

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

void loop() {
  // Read the photoresistor's analog value
  int ldrValue = analogRead(ldrPin);
  
  // Print the value to the serial monitor
  Serial.print("Light level: ");
  Serial.println(ldrValue);
  
  // Wait for a short while before reading again
  delay(500);
}

4. Test the Circuit

1. Upload the code to your Arduino.
2. Open the Serial Monitor (Tools > Serial Monitor).
3. Observe the values changing as you cover the photoresistor or expose it to light.
4. Approximate values:
   • Complete darkness: 0-100
   • Dim room: 300-500
   • Bright light: 800-1023

5. Calibration (Optional)

For more precise readings, you can calibrate your circuit:

// Define your own thresholds based on your environment
const int darkThreshold = 200;

const int brightThreshold = 800;

void loop() {
  int ldrValue = analogRead(ldrPin);

  if (ldrValue < darkThreshold) {
    Serial.println("Dark");
  }
  else if (ldrValue > brightThreshold) {
    Serial.println("Bright");
  }
  else {
    Serial.println("Medium light");
  }

  delay(500);
}

Here is the output that the serial monitor displays when uploading the code to the arduino. The light value ranges from 0 - 1023.

Applications

This basic circuit can be used for:

• Automatic night lights
• Light-activated switches
• Plant monitoring systems
• Simple security systems (detect lights being turned on/off)

Troubleshooting

1. No change in values:

   • Check connections
   • Make sure the photoresistor is not damaged (check resistance with a multimeter)

2. Values stuck at 0 or 1023:

   • Check for short circuits or open connections
   • Make sure resistor value is correct (10kΩ)

3. Unstable readings:

• Connect a small capacitor (0.1µF) between A0 and GND to filter out reading fluctuations
  • Check for loose connections

Expanding the Circuit

You can combine this with other components like:

• An LED that will turn on when the light goes dark
• A relay to turn on/off lights automatically
• An LCD display to show light levels