How to Use HC-SR501 PIR: Examples, Pinouts, and Specs

The HC-SR501 is a passive infrared (PIR) motion sensor designed to detect motion by sensing changes in infrared radiation emitted by objects within its detection range. This component is widely used in security systems, home automation, and DIY electronics projects. It is particularly popular for triggering alarms, lights, or other devices when motion is detected.

• Security systems for detecting intruders
• Automatic lighting systems
• Motion-activated cameras
• Home automation projects
• Robotics and interactive installations

The HC-SR501 PIR sensor is a versatile and adjustable module with the following key specifications:

The HC-SR501 PIR sensor has three pins for interfacing:

1. Power Supply: Connect the VCC pin to a DC power source (4.5V to 20V) and the GND pin to ground.
2. Output Signal: Connect the OUT pin to a microcontroller (e.g., Arduino) or directly to a device (e.g., an LED or buzzer) to receive the motion detection signal.
3. Adjustments:
   • Use the sensitivity potentiometer to adjust the detection range (clockwise to increase).
   • Use the time delay potentiometer to set the duration for which the output remains HIGH after motion is detected.

Below is an example of how to connect and program the HC-SR501 PIR sensor with an Arduino UNO to control an LED:

• Connect the VCC pin of the HC-SR501 to the Arduino's 5V pin.
• Connect the GND pin of the HC-SR501 to the Arduino's GND pin.
• Connect the OUT pin of the HC-SR501 to digital pin 2 on the Arduino.
• Connect an LED to digital pin 13 on the Arduino with a 220-ohm resistor.

// HC-SR501 PIR Motion Sensor Example with Arduino UNO
// This code turns on an LED when motion is detected.

#define PIR_PIN 2       // HC-SR501 OUT pin connected to digital pin 2
#define LED_PIN 13      // LED connected to digital pin 13

void setup() {
  pinMode(PIR_PIN, INPUT);  // Set PIR sensor pin as input
  pinMode(LED_PIN, OUTPUT); // Set LED pin as output
  Serial.begin(9600);       // Initialize serial communication for debugging
}

void loop() {
  int motionDetected = digitalRead(PIR_PIN); // Read PIR sensor output

  if (motionDetected == HIGH) { // If motion is detected
    digitalWrite(LED_PIN, HIGH); // Turn on the LED
    Serial.println("Motion detected!"); // Print message to serial monitor
  } else {
    digitalWrite(LED_PIN, LOW); // Turn off the LED
  }

  delay(100); // Small delay to stabilize readings
}

• Warm-Up Time: The HC-SR501 requires a warm-up period of approximately 30 to 60 seconds after powering on to stabilize its readings.
• Avoid Direct Sunlight: The sensor may not function correctly in direct sunlight or near heat sources.
• Trigger Modes:
  • Repeatable Mode (default): The output remains HIGH as long as motion is detected.
  • Non-Repeatable Mode: The output goes LOW after the set time delay, even if motion is still present. This mode can be configured by adjusting the onboard jumper.

1. No Motion Detected:

   • Ensure the sensor is properly powered (4.5V to 20V DC).
   • Verify that the warm-up period has completed.
   • Check the sensitivity potentiometer and adjust if necessary.

2. False Triggers:

   • Avoid placing the sensor near heat sources, reflective surfaces, or moving objects like fans.
   • Ensure stable power supply voltage.

3. Output Stays HIGH:

   • Check if the time delay potentiometer is set too high.
   • Verify the trigger mode jumper setting.

4. Short Detection Range:

   • Adjust the sensitivity potentiometer clockwise to increase the range.
   • Ensure there are no obstructions in the sensor's field of view.

Q1: Can the HC-SR501 detect motion through glass?
A1: No, the HC-SR501 cannot detect motion through glass as infrared radiation does not pass through it effectively.

Q2: What is the maximum detection range of the HC-SR501?
A2: The maximum detection range is approximately 7 meters, depending on the sensitivity setting and environmental conditions.

Q3: Can I power the HC-SR501 with a 3.3V supply?
A3: No, the minimum operating voltage is 4.5V. Use a power supply within the 4.5V to 20V range.

Q4: How do I switch between trigger modes?
A4: Use the onboard jumper to toggle between repeatable and non-repeatable modes. Refer to the module's markings for guidance.

By following this documentation, you can effectively integrate the HC-SR501 PIR sensor into your projects and troubleshoot common issues with ease.