2.31 PIR Module

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Overview

In this lesson, you will learn how to use PIR Module. The PIR sensor detects infrared heat radiation or the presence of organisms that emit infrared heat radiation. This module is widely used in daily life for our intruder alarm and visiting prompt.

Components Required

Component Introduction

The PIR sensor is split into two slots that are connected to a differential amplifier. Whenever a stationary object is in front of the sensor, the two slots receive the same amount of radiation and the output is zero. Whenever a moving object is in front of the sensor, one of the slots receives more radiation than the other, which makes the output fluctuate high or low. This change in output voltage is a result of detection of motion.

After the sensing module is wired, there is a one-minute initialization. During the initialization, module will output for 0~3 times at intervals. Then the module will be in the standby mode. Please keep the interference of light source and other sources away from the surface of the module so as to avoid the misoperation caused by the interfering signal. Even you’d better use the module without too much wind, because the wind can also interfere with the sensor.
Two trigger modes: (choosing different modes by using the jumper cap).

Distance Adjustment

Turning the knob of the distance adjustment potentiometer clockwise, the range of sensing distance increases, and the maximum sensing distance range is about 0-7 meters. If turn it anticlockwise, the range of sensing distance is reduced, and the minimum sensing distance range is about 0-3 meters.

Delay Adjustment
Rotate the knob of the delay adjustment potentiometer clockwise, you can also see the sensing delay increasing. The maximum of the sensing delay can reach up to 300s. On the contrary, if rotate it anticlockwise, you can shorten the delay with a minimum of 5s. 

Two trigger modes: (choosing different modes by using the jumper cap).

  • H: Repeatable trigger mode, after sensing the human body, the module outputs high level. During the subsequent delay period, if somebody enters the sensing range,the output will keep being the high level.
  • LNon-repeatable trigger mode, outputs high level when it senses the human body. After the delay, the output will change from high level into low level automatically. 

PIR can only be installed indoors, and its false alarm rate has a great relationship with the location and mode of installation. The correct use should meet the following conditions:
1. It should be 2.0-2.2 meters above the ground.
2. Stay away from air conditioners, refrigerators, stoves and other places where air temperature changes apparently.
3. No screen, furniture, large-scale bonsai or other isolation objects shall be detected within the detection range.
4. Don’t face straightly toward the window, otherwise the disturbance of the hot air flow outside the window and the movement of people will cause false alarm.
5. Do not use in areas with strong airflow.
6. The sensitivity of PIR to human body is also closely related to the direction of movement. It is least sensitive to radial movement and most sensitive to the movement in the crosscutting direction.

Fritzing Circuit

In this example, we can connect the pins of Sound Sensor Module to the pins of Mega 2560 Board directly, and we use digital pin 2 to read the signal of PIR Module. Connect the VCC of PIR Module to 5V, GND to GND, and OUT to digital pin NOTE: you can remove the PIR cover to see the pin mark.

Schematic Diagram

Code

void setup() {
  Serial.begin(9600);
  pinMode(2, INPUT);
}

void loop() {
  Serial.println(digitalRead(2));
  delay(1);      
}

After the codes are uploaded to the Mega2560 board, you can open the serial monitor to see the reading value of the pin. When PIR Module detects activity nearby, the serial monitor will display 「1」; otherwise, it will display 「0」. Check Part 1-1.4 Digital Read for more detail code explanation.

There are two potentiometers on the PIR module: one is to adjust sensitivity and the other is to adjust the detection distance. In order to make the PIR module work better, you need to try to adjust these two potentiometers.

Phenomenon Picture