Tuesday, October 20, 2020
Home Arduino Passive Infrared Sensor HC-SR501 | PASSIVE INFRARED SENSOR

HC-SR501 | PASSIVE INFRARED SENSOR

HC-SR501 is a Passive Infrared Sensor. It measures the surrounding Infrared radiation coming from bodies. It is mostly used for Arduino security projects like burglar alarms, etc. The sensor can’t get the information on who moved or what moved, so it is called Passive Infrared device.If you are looking for mini version check out the HC-SR505

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HC-SR501 Module
HC-SR501 Module

Specification

  • Voltage: 5V – 20V
  • Power Consumption: 65mA
  • TTL output: 3.3V, 0V
  • Delay time: Adjustable (.3->5min)
  • Lock time: 0.2 sec
  • Trigger methods: L – disable repeat trigger, H enable repeat trigger
  • Sensing range: less than 120 degrees, within 7 meters
  • Temperature: – 15 ~ +70
  • Dimension: 32*24 mm, the distance between screw 28mm, M2, Lens dimension in diameter: 23mm

How does HC-SR501 work?

 

Every living body emits heat energy in the form of radiation. HC-SR501 is designed to detect such radiations. There is two component of the sensor. The Pyroelectric sensor and the fresnel lens. This lens focuses the infrared signals onto the pyroelectric sensor. There are two slots in the pyroelectric sensors. Behind these two slots, there are two sensor electrodes.

  • One responsible for positive output.
  • Second for negative output

When there is no movement both sides of the slot have the same outputs. This is the situation when the sensor is idle. When a warm body passes, half of the sensor causes a positive differential change. The reverse happens when the warm body leaves the sensing area. The sensor generates a negative differential change. The Corresponding pulse of signals results in the sensor setting its output pin high.

HC-SR501 Pinouts

The sensor has 3 pins

  • Vcc
  • GND
  • Output

There are two potientiometers to set the sensitivity and running time of the module.

Arduino Wiring:

First, Connect the Sensor VCC to Arduino VCC.

Then Connect Sensor GND to Arduino GND

Lastly, Connect Sensor Output to Arduino  pin 13

Arduino Code:

/*
 * PIR sensor tester
 */
 
int ledPin = 10;                // choose the pin for the LED
int inputPin = 2;               // choose the input pin (for PIR sensor)
int pirState = LOW;             // we start, assuming no motion detected
int val = 0;                    // variable for reading the pin status
 
void setup() {
  pinMode(ledPin, OUTPUT);      // declare LED as output
  pinMode(inputPin, INPUT);     // declare sensor as input
 
  Serial.begin(9600);
}
 
void loop(){
  val = digitalRead(inputPin);  // read input value
  if (val == HIGH) {            // check if the input is HIGH
    digitalWrite(ledPin, HIGH);  // turn LED ON
    if (pirState == LOW) {
      // we have just turned on
      Serial.println("Motion detected!");
      // We only want to print on the output change, not state
      pirState = HIGH;
    }
  } else {
    digitalWrite(ledPin, LOW); // turn LED OFF
    if (pirState == HIGH){
      // we have just turned of
      Serial.println("Motion ended!");
      // We only want to print on the output change, not state
      pirState = LOW;
    }
  }
}

 

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