PIR Motion Detector Module

A passive infrared (PIR) detector is a device which responds to the level of infrared radiation hitting its surface. Higher radiation increases the output voltage, which is amplified and compared to a high and low reference. Any voltage exceeding either reference will trigger the output.

The ones I picked up on ebay have a BISS0001 PIR motion detector chip, which contains the amplifiers and comparators necessary to make a complete motion detector. They have adjustments for sensitivity and time delay. You can adjust both how likely it is to trigger, and how long it will wait after an event before triggering, which helps prevent it from triggering on noise and flashes of light.

The PIR sensor on the front of the board

The sensor is actually two sensors in one, and the signal is the difference between them. The amplifier IC just amplifies and compares. Some logic in the IC includes the ability to retrigger, test the device, and prevent it from working in well lighted rooms, which can blind the sensor or cause false triggers.

It has a lens designed to see a cone of about 130°, so it does not ignore objects lower than a standing human.

What it has going for it is the fact that it is 1" x 1.25" and only draws 90µA when idle and 130µA when triggered. Excellent figures for battery operation. And small enough to hide. It can sense someone appearing in a doorway from 20 feet. It is a great sensor module for experimentation and for people detecting. Maybe not sophisticated enough to use as a burglar alarm.

More elaborate motion detectors use both of the signals from the two sensors in the PIR detector independently, running them through a differential amplifier, which cancels out the room's ambient infrared, and causes it to detect only the changes in the infrared background (motion). They also reduce the possibility of electromagnetic interference causing false triggers.

The sensor hooks to an Arduino Uno with one signal wire, +5V, and ground. You can run this sensor on a digital output, rather than the +5V if you choose, since the power draw is so very low. To do that, just run the VCC pin on the PIR sensor module to a digital output, and add two lines of code to setup:


  pinMode(4, OUTPUT);
  digitalWrite(4, HIGH);
            

void setup() {

  pinMode(2, INPUT);
  pinMode(3, OUTPUT);
}

void loop() {

  digitalWrite(3, !digitalRead(2));
}
    

The program simply writes the opposite of anything it reads from the sensor to the LED. The sensor's output is normally low, the LED output is high, and the LED is off. When the sensor detects an object the output goes high, so the LED output goes low, and the LED goes on.

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