PIR sensors allow you to sense motion. They are used to detect
whether a human has moved in or out of the sensor’s range. They are
commonly found in appliances and gadgets used at home or for businesses.
They are often referred to as PIR, "Passive Infrared", "Pyroelectric",
or "IR motion" sensors.
Following are the advantages of PIR Sensors −
PIRs are made of pyroelectric sensors, a round metal can with a
rectangular crystal in the center, which can detect levels of infrared
radiation. Everything emits low-level radiation, and the hotter
something is, the more radiation is emitted. The sensor in a motion
detector is split in two halves. This is to detect motion (change) and
not average IR levels. The two halves are connected so that they cancel
out each other. If one-half sees more or less IR radiation than the
other, the output will swing high or low.
PIRs have adjustable settings and have a header installed in the 3-pin ground/out/power pads.
For many basic projects or products that need to detect when a person
has left or entered the area, PIR sensors are great. Note that PIRs do
not tell you the number of people around or their closeness to the
sensor. The lens is often fixed to a certain sweep at a distance and
they are sometimes set off by the pets in the house.
Once the sensor detects any motion, Arduino will send a message via
the serial port to say that a motion is detected. The PIR sense motion
will delay for certain time to check if there is a new motion. If there
is no motion detected, Arduino will send a new message saying that the
motion has ended.
Following are the advantages of PIR Sensors −
- Small in size
- Wide lens range
- Easy to interface
- Inexpensive
- Low-power
- Easy to use
- Do not wear out

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Components Required
You will need the following components −- 1 × Breadboard
- 1 × Arduino Uno R3
- 1 × PIR Sensor (MQ3)
Procedure
Follow the circuit diagram and make the connections as shown in the image below.
Sketch
Open the Arduino IDE software on your computer. Coding in the Arduino language will control your circuit. Open a new sketch File by clicking New.
Arduino Code
#define pirPin 2 int calibrationTime = 30; long unsigned int lowIn; long unsigned int pause = 5000; boolean lockLow = true; boolean takeLowTime; int PIRValue = 0; void setup() { Serial.begin(9600); pinMode(pirPin, INPUT); } void loop() { PIRSensor(); } void PIRSensor() { if(digitalRead(pirPin) == HIGH) { if(lockLow) { PIRValue = 1; lockLow = false; Serial.println("Motion detected."); delay(50); } takeLowTime = true; } if(digitalRead(pirPin) == LOW) { if(takeLowTime){ lowIn = millis();takeLowTime = false; } if(!lockLow && millis() - lowIn > pause) { PIRValue = 0; lockLow = true; Serial.println("Motion ended."); delay(50); } } }
Code to Note
PIR sensor has three terminals - Vcc, OUT and GND. Connect the sensor as follows −- Connect the +Vcc to +5v on Arduino board.
- Connect OUT to digital pin 2 on Arduino board.
- Connect GND with GND on Arduino.
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