Working with PIR sensor on Arduino

PIR Sensor

PIR Sensor stands for Pyroelectric (passive) InfraRed sensor, which allows us to detect human or object movement within a certain range. They are small, low-cost, low-power, easy to use and long lasting. PIR sensors are adopted in myriads of projects as they are easy to use with popular hardwares such as Arduino and raspberry pi. PIR sensors are commonly used in security alarms and automatic lighting applications.

Working of PIR sensor

PIRs are basically made of a pyroelectric sensor, which can detect levels of infrared radiation and convert IR energy to electrical signal. All bodies with temperature above absolute zero (0 K) emit infra-red radiation. The higher the temperature, the more radiation is emitted. The sensor in a motion detector is actually split in two halves. When a body moves, the sensor detects change in IR levels. The two halves are connected in a way so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low.

If the human infrared radiation is directly irradiated on the detector, it will output a signal. The signal strength depends on distance from body.  Farther the distance, lesser is the irradiation on sensor and lesser is the sensitivity. In order to lengthen the detection distance of the detector, an optical system is added to focus the infrared radiation, usually using a plastic optical reflection system or a Fresnel lens made of plastic as a focusing system for infrared radiation.

In the detection area, the infrared radiation energy of the human body through the clothing is received by the lens of the detector and focused on the pyroelectric sensor. The detector can sense the human body within a field of view . The pyroelectric sensor sees the moving human body till it is within field of view and then does not see it beyond that. The infrared radiation constantly changes the temperature of the pyroelectric material so that it outputs a corresponding signal, which is the alarm signal.

Most PIR sensors have a 3-pin connection at the side or bottom. One pin will be ground, another will be signal and the last pin will be power. Power is usually up to 5V. Interfacing PIR with Arduino is very easy and simple. The PIR acts as a digital output so all you need to do read the output state as HIGH or LOW. The motion can be detected by checking for a high signal on a single I/O pin. Once the sensor warms up the output will remain low until there is motion, at which time the output will swing high for a couple of seconds, then return low. If motion continues the output will cycle in this manner until the sensors line of sight of still again. The PIR sensor needs a warm-up time with a specific end goal to capacity fittingly. The settling is adjustable from 10-60 seconds.

The Range of PIR Sensor

Indoor passive infrared: 25 cm to 20 m.

Indoor curtain type: 25 cm to 20 m.

Outdoor passive infrared: 10 meters to 150 meters.

Outdoor passive infrared curtain detector: 10 meters to 150 meters

Interfacing with Arduino

There are three pins in the PIR sensor- Vcc, OUTPUT, GND. We connect Vcc pin to +5V terminal of Arduino, GND to Ground pin and OUTPUT to any digital input pin of arduino.

Arduino code

/*

  DigitalReadSerial

  Reads a digital input on pin 8, prints the result to the Serial Monitor

// digital pin 12 has a LED attached to it.

int PIR_OUT = 8;

int LED = 12;

// the setup routine runs once when you press reset:

void setup() {

  // initialize serial communication at 9600 bits per second:

  Serial.begin(9600);

  // make the pushbutton's pin an input:

  pinMode(PIR_OUT, INPUT);

  pinMode(LED, INPUT);

}

// the loop routine runs over and over again forever:

void loop() {

  // read the input pin:

  int State = digitalRead(PIR_OUT);

  // print out the state of the button:

  Serial.println(State);

  digitalWrite(LED, State);

  delay(200);        // delay in between reads for stability

}