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Introduction to PIR Sensor

PIR sensors detect motion and are always used to determine whether a human has entered or exited the sensor’s range. They’re small, cheap, low-power, simple to use, and they don’t wear out. As a result, they’re often found in home and business equipment and gadgets.In this blog, we discuss about the PIR sensor, its operating principle,features etc

WHAT IS A PIR SENSOR?

A Passive Infrared sensor defined as an electrical sensor that detects the infrared light radiated by a warm object or used to sense motion. It is widely used to detect the motion of a human body within the sensor’s range. Hence often referred to as “PIR”, “Pyroelectric”, “Passive Infrared” and “IR Motion” sensor.

PIR sensor senses infrared energy emits the human body within a detection area of approximately 3-7 meters. When the human body moves within the detection range at a certain field of view in sequence and then walks out of the field of view. As a result, the pyroelectric sensor senses the moving human body for a while and then does not see it, so the infrared radiation of the human body constantly changes the temperature of the pyroelectric material. Thus outputs a corresponding signal, which is the alarm signal. This sensor offers a wide range of applications in burglar alarms and automatically-activated lighting systems etc.

The module consists of an on-board pyroelectric sensor, conditioning circuitry, and a dome-shaped Fresnel lens. In addition to it, it consists of a delay time adjustment Potentiometer and sensitivity adjustment Potentiometer. These pyroelectric sensors introduce changes in their temperature due to incident infrared radiation into an electric signal. But there will be no change in the detection distance. In order to lengthen the detection distance of the detector, an optical system added to collect the infrared radiation. Usually, a plastic optical reflection system or plastic Fresnel lens used as a focusing system for infrared radiation. These small, inexpensive, low-power sensors can be easily interfaced with ARDUINO, RASPBERRY PI, AVR, PIC, 8051, etc.

Features:

  • Complete with PIR, Motion Detection.
  • Dual Element Sensor with Low Noise and High Sensitivity.
  • Supply Voltage – 5V.
  • Delay Time Adjustable.
  • Standard TTL Output.
  • Sensitivity Adjustable: Turn On Lights during Day or nights
  • Automatic On & Off Lights
  • Wide operating range
  • Good solution for energy saving & easy in installation
  • Delay adjustment: 10 Seconds – 7 Minutes 
  • Adjustable Lux: turn on the lights during the day or night

Illustration of PIR sensitive crystal:

The IR sensitive crystal, which is contained in the black area of the metal, can detect the level of infrared in the environment. It contains two pyroelectic sensors that detect moving things. The output is activated if one of the sensitive crystals detects a greater change in infrared (increment or decrement) than the other sensitive crystal. A dome shaped plastic structure is normally placed over this sensitive crystal which acts as lens to focus the infrared light on the sensors.

 PIR Sensor IC PINOUT

The PIR sensor IC consists of 3 pins-  Vcc, Ground and Output.

  • Pin1: Corresponds to the drain terminal of the device, which is connected to the positive supply 5V DC.
  • Pin 2: Corresponds to the source terminal of the device, which connects to the ground terminal via a 100K or 47K resistor.  The measured IR signal is sent to an amplifier through pin 2 of the sensor, which is connected to the ground.
  • Pin 3: Connected to the ground.

The sensor detects human IR radiations and converts them directly to electrical pulses, which are then sent to the inverter circuit. The inverter circuit consists of a transistor that becomes saturated when a large base current is applied, resulting in a low collector voltage. As a result, the transistor output is quite low.The microcontroller is connected to the low inverter output. The microprocessor controls the motor driver, which controls the motor’s motion, based on the input it receives.

What is the Range of PIR Sensor?

  • Indoor passive infrared: Detection distances range from 25 cm to 20 m.
  • Indoor curtain type: The detection distance ranges from 25 cm to 20 m.
  • Outdoor passive infrared: The detection distance ranges from 10 meters to 150 meters.
  • Outdoor passive infrared curtain detector: distance from 10 meters to 150 meters

How PIR Works?

Passive infrared (PIR) sensors use a pair of pyroelectric sensors to detect heat energy in the surrounding environment. These two sensors sit beside each other, and when the signal differential between the two sensors changes (if a person enters the room, for example), the sensor will engage. That may mean it triggers an alarm, notifies authorities, or maybe turns on a floodlight. IR radiation focuses on each of the two pyroelectric sensors using a series of lenses constructed as the sensor’s housing. These lenses widen the device’s sensing area.

These sensors employing a dual or a pair of sensing elements for sensing the IR signals in two steps,ensures a foolproof detection by cancelling the unwanted temperature variations within the existing EMI stage. This two-step sensing process improves the overall stability of the sensor and helps to detect IR signals only from human presence.

When a human being or a relevant IR source moves past a PIR sensor, the radiation cuts into the pair of sensing elements in an alternate manner, triggering the output to generate a pair of ON/OFF or high and low pulses, as depicted in the following waveform:

PIR Sensor output pulse waveform

Applications of PIR Sensors   

  • All outdoor Lights
  • Lift Lobby
  • Multi Apartment Complexes
  • Common staircases
  • For Basement or Covered Parking Area
  • Shopping Malls
  • For garden lights

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