How to Use Light Sensor w Relay: Examples, Pinouts, and Specs

The XHM131 Light Sensor w Relay is a versatile electronic component designed to detect ambient light levels and activate a relay based on user-defined thresholds. This component is ideal for automating devices such as lights, fans, or other appliances, making it a popular choice for home automation, industrial applications, and DIY projects. Manufactured in China, the XHM131 combines a light-dependent resistor (LDR) for light detection and a relay module for switching high-power devices.

• Automatic lighting systems (e.g., streetlights, garden lights)
• Smart home automation
• Energy-saving systems
• Industrial equipment control
• DIY electronics projects

• Manufacturer Part ID: XHM131
• Operating Voltage: 5V DC
• Relay Output Voltage: 250V AC / 30V DC (max)
• Relay Output Current: 10A (max)
• Light Detection Range: Adjustable via onboard potentiometer
• Trigger Type: Light-dependent (adjustable threshold)
• Dimensions: 50mm x 26mm x 19mm
• Operating Temperature: -40°C to 85°C

The XHM131 module has a total of 6 pins and terminals for input and output connections. Below is the pinout description:

1. Power the Module: Connect the VCC pin to a 5V DC power source and the GND pin to ground.
2. Adjust the Sensitivity: Use the onboard potentiometer to set the light threshold at which the relay activates.
3. Connect the Load:
   • For devices that should turn ON when light is detected, connect the load between the NO (Normally Open) and COM (Common) terminals.
   • For devices that should turn OFF when light is detected, connect the load between the NC (Normally Closed) and COM terminals.
4. Monitor the Output: The OUT pin provides a digital signal (HIGH or LOW) that can be read by a microcontroller like an Arduino.

• Power Supply: Ensure a stable 5V DC power supply to avoid erratic behavior.
• Load Ratings: Do not exceed the relay's maximum voltage (250V AC / 30V DC) or current (10A).
• Isolation: For safety, ensure proper isolation between the high-voltage relay terminals and the low-voltage control circuit.
• Potentiometer Adjustment: Turn the potentiometer clockwise to increase the light threshold or counterclockwise to decrease it.
• Mounting: Secure the module in a well-ventilated area to prevent overheating.

Below is an example of how to use the XHM131 with an Arduino UNO to control an LED based on ambient light levels.

• Connect the VCC and GND pins of the XHM131 to the 5V and GND pins of the Arduino, respectively.
• Connect the OUT pin of the XHM131 to Arduino digital pin 2.
• Connect an LED to the NO and COM terminals of the relay, with a suitable resistor in series.

// Define the pin connected to the XHM131 OUT pin
const int lightSensorPin = 2;  
// Define the pin connected to the relay (NO terminal)
const int relayPin = 13;  

void setup() {
  pinMode(lightSensorPin, INPUT);  // Set the light sensor pin as input
  pinMode(relayPin, OUTPUT);       // Set the relay pin as output
  digitalWrite(relayPin, LOW);     // Ensure the relay is off initially
  Serial.begin(9600);              // Initialize serial communication
}

void loop() {
  int lightStatus = digitalRead(lightSensorPin);  // Read the light sensor output
  
  if (lightStatus == HIGH) {
    // If light is detected, activate the relay
    digitalWrite(relayPin, HIGH);
    Serial.println("Light detected: Relay ON");
  } else {
    // If no light is detected, deactivate the relay
    digitalWrite(relayPin, LOW);
    Serial.println("No light detected: Relay OFF");
  }
  
  delay(500);  // Add a small delay for stability
}

1. Relay Not Activating

   • Cause: Insufficient power supply or incorrect wiring.
   • Solution: Verify that the VCC pin is receiving a stable 5V DC and check all connections.

2. Erratic Behavior

   • Cause: Electrical noise or unstable power supply.
   • Solution: Use a decoupling capacitor (e.g., 100µF) across the VCC and GND pins to stabilize the power supply.

3. Relay Stuck in One State

   • Cause: Incorrect potentiometer adjustment.
   • Solution: Adjust the potentiometer to set the desired light threshold.

4. Arduino Not Detecting Output

   • Cause: Incorrect pin configuration or faulty module.
   • Solution: Ensure the OUT pin is connected to the correct Arduino pin and test the module with a multimeter.

• Q: Can the XHM131 detect specific light wavelengths?
  A: No, the XHM131 uses an LDR, which responds to general ambient light levels and is not wavelength-specific.

• Q: Can I use the XHM131 with a 3.3V microcontroller?
  A: The module requires a 5V power supply, but the OUT pin can be connected to a 3.3V logic input with proper level shifting.

• Q: Is the relay safe for inductive loads like motors?
  A: Yes, but use a flyback diode across the load to protect the relay from voltage spikes.

This concludes the documentation for the XHM131 Light Sensor w Relay.