Arduino Lesson 17: Using a PIR

Posted on 26/09/2014 by admin Δημοσιεύτηκε στο Arduino Lessons, Arduino Μαθήματα — Δεν υπάρχουν σχόλια ↓

Overview
Parts
How PIR Work ?
The Breadboard Layout
Arduino Code

Overview

PIR sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range. They are small, inexpensive, low-power, easy to use and don’t wear out. For that reason they are commonly found in appliances and gadgets used in homes or businesses. They are often referred to as PIR, “Passive Infrared”, “Pyroelectric”, or “IR motion” sensors.

Parts

To build the projects described in this lesson, you will need the following parts.

1 PIR Motion Sensor

Half-size Breadboard

Arduino Uno R3

Jumper wire pack

How PIRs Work?

The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR.

The lens used here is not really doing much and so we see that the two slots can ‘see’ out past some distance (basically the sensitivity of the sensor).

When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor, which causes a positive differential change between the two halves.

When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected.

The Breadboard Layout

Most PIR modules have a 3-pin connection at the side or bottom.

Connecting PIR sensors to a microcontroller is really simple. The PIR acts as a digital output so all you need to do is listen for the pin to flip high (detected) or low (not detected).

Power the PIR with 5V and connect ground to ground. Then connect the output to a digital pin. In this example we’ll use pin 7.

To connect your PIR sensor to your arduino follow the instructions by the image above.

VCC Pin to +5V of Arduino and GND Pin to GND (Ground) of your Arduino Board. Then connect the signal pin to the digital 7 pin of Arduino.

Arduino Code

The code is very simple, and is basically just keeps track of whether the input to pin 7 is high or low. It also tracks the state of the pin, so that it prints out a message when motion has started and stopped.

/*
* PIR sensor tester
*/
int ledPin = 13; // choose the pin for the LED
int inputPin = 7; // 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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