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What do you need to know about PIR Sensor?

PIR sensors play vital roles in modern daily life. No one can imagine starting without them, as they are present in almost all modern devices because of their amazing features, which include consistency, easy usage, and cost-efficient.

These sensors are mainly used in security alarms. Door openings, lift lobbies, vending machines, auto light switches, and much more. Moreover, as these sensors give a variety of benefits, it also takes part in projects like Arduino and Raspberry. This article, however, tells you about PIR sensors, their usage, applications, and working principles. 

What Is PIR Sensor?

Passive Infrared or PIR sensor refers to a type of sensor that helps in measuring the light of infrared radiation coming from objects such as animals or the human body. PIR sensor has the ability to detect or identify human or animal movement in a specified range. Typically, every object that has a body temperature above zero produces heat in the form of IR radiation. Therefore, the higher the temperature of the object, the greater the radiation. Moreover, the human eye cannot see or observe these radiations because of theIR wavelength it emits. Thus, PIR sensors are basically made to detect and sense these types of infrared radiation. It usually uses in motion sensor devices, auto light switches, and security alarms.

Working Principle of PIR Sensor

PIR Sensor
PIR Sensor

The PIR sensor contains two basic components. This includes a fresnel lens and pyroelectric sensor. The sensor comes in a circular metal form which contains a crystal in a rectangular form right in the middle of it.

However, the fresnel sense refers to a type of lens that identifies the infrared signals through a pyroelectric sensor. Moreover, a pyroelectric sensor can detect various levels of infrared radiation.

The Pyroelectric Sensor

A pyroelectric sensor contains a window with two slots in a rectangular form. Moreover, it comprises silicon coating, which allows the infrared radiation to flow simply. Then, it has two separate electrodes of the Infrared sensor. In both of these electrodes, one produces positive output while the other produces negative output. 

However, when the movement in the sensor region stops, then both rectangular slots identify similar Infrared radiation, which gives zero positive output signal. Even when the body of an animal or human moves in a sensor region, it just interrupts half of the sensor first. Thus causing a positive change between the two parts. However, when the body moves through the other half, it generates the opposite result, a negative output signal. The changes between the voltages detect the motion.

Fresnel Lens

A Fresnel lens basically enhances the field and capacity of view of sensors. It contains the capacity to gather light as well as being compact and lightweight. Hence making the size of the sensor small yet powerful.

When the body of an animal or human enters the sensor detecting range, the sensor automatically starts getting the IR wavelength of the light from the object. When it detects the infrared waves, it automatically turns on the light. However, when a body does not pass through the range, the sensor cannot sense any wave and automatically turns off the light. So a type of sensor that senses waves and switches lights is called a Passive IR sensor light. Moreover, if an object or body remains in the detecting place, the light also stays on constantly. But as the body or object leaves the detecting place, the delay automatically turns off the light.

Specification & Characteristics of PIR Sensor

PIR sensors offer various types of specifications and features. Some of them include voltage supply input and output. The input must range from +5 Volts, while the output voltage must range to 3.3 volts. It does not detect the human or object but also differentiates between them properly. Moreover, it contains both non-repeatable and repeatable operation modes. The drain of the current must stay above 60uA while the angle of detection must stay above 140 degrees. At the same time, it offers a distance of detection ranging from 7 to 3m. It contains a 2.5s blockade time default. Lower utilization of power must range 65mA while working temperature between+80 -20°C. 

Different Types of PIR Sensors

Passive Infrared sensors have two types. These types include;

· Thermal Infrared Sensor

Pyroelectric IR sensor or Thermal IR sensor uses thermal sources such as infrared, which helps in detecting objects. These sensors process slowly and give slow detection and response time.

· Quantum Infrared Sensor

Quantum IR refers to a type of sensor that detects or identifies photos present over the wavelength. However, these photons respond more quickly than detecting heat. This type of sensor operates efficiently and has fast detection and response time. Though, it requires a proper and constant cooling mechanism to measure the exact location.

Circuit Diagram Explanation of PIR Sensor

PIR sensor proves ideal for installing in security systems. It offers features like robustness and low cost, which makes it perfect to use in the design of security circuits. The PIR sensor supports the circuit to make a motion detector device along with a relay.

This relay turns on the light as the motion detector senses any human movement. Motion detector PIR circuit requires a few basic components to make. This includes a PIR sensor, A relay of 5 V, a BC547 transistor, a 1N4007 diode, a 1k Ohm resistor, an electric bulb, and a 9 V battery.

Major Applications Of PIR Sensor


Passive Infrared sensors are used in a variety of applications and devices in distinct fields. These fields include a lift lobby, outdoor light automatic switching, and covered parking lots. Moreover, it also uses automatic switches for garden lights which work on the human presence. Also it is used in automatic doors of shopping malls which also works on sensing a human presence. Here are two basic yet innovative design projects of PIr sensors. 

· Automatic Door Opening System

The latest, innovative automatic door system uses a PIR sensor to operate. When a human goes through an automatic door, the sensor produces output pulses.

However, these pulses go to a microcontroller. This microcontroller controls and manages the motor driver. It accepts the input pulses and enables the motor driver to work appropriately.

· Security Alarm System

Banks and big companies that need utter safety of their assets use security systems. These systems use PIR sensors to work. The circuit contains IC UM3561. It refers to a type of integrated circuit.

This special IC takes input in digital signals and produces multi tones for the alarm like police, ambulance, and fire brigade sirens. Like other sensors, it detects the presence of humans as one passes through it, and it gives output in digital form. This output goes to the IC UM3561, which produces the desired siren.

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