PIR motion sensor

 Types of Human Body Detection Sensors 

1. Image Sensors
2. Active Sensors
3. Passive Sensors

Image Sensors- 

•  Detects human body from image data .
•  Advanced processing is a possible
• Issue for privacy

Active Sensors

• Detects presence or absence of people from reflected wave. such as sound , radio and light.
• Detection angle is narrow.
• Limited distance.
• Large current consumption.

Passive Sensors

• Receive infrared energy radiating from the object's surface , detects human body.
• Detection angle is wide.
• Low current consumption. 

What is PIR Motion Sensor ?

Passive infrared sensor.

How PIR motion sensor works?

All objects with temperature above absolute Zero ( 0 kelvin \-273.15 °C ) emit head energy in the form of infrared radiation, including human bodies.The hotter an object is, the more radiation it emits.

When the sensor is idle, i.e. there is no movement around the sensor both slots detect the same amount of infrared radiation, resulting in a zero output signal.

Operating voltage range: DC4.5 5-20V

Quiescent Current: <60uA

Trigger: reusable trigger (default)

Delay Time: The default 8S + -30%

Board Dimensions: 10 * 23mm

Induction angle: <100 degrees cone angle

Sensing distance 3 meters

Working temperature: -20 to +80 degrees

Sensor Lens Dimensions: Diameter 10mm

PIR Sensor Specification

Current drain:<60uA

Voltage Output: High/Low level signal: 3.3V TTL output

Detection distance: 3-7M (can be adjusted)

Detection range: < 120°

Delay time: 5-200S (can be adjusted, default 5s +-3%)

Trigger: Non-repeatable trigger H: Repeat Trigger (default)

Trigger Method: L unrepeatable trigger / H repeatable trigger

PIR Sensor application

• Sleep Detection 
• Motion Detection
• Smart Door Opener
• Theft Seqrity Alarm

Operating Principal

All Object with a temperature above absolute zero emit heat energy in the from of electromagnetic radiation. Usually this radiation is not visible to the human eye because it radiates at infrared wavelengths, but it can be detected by electronic devices designed for such a purpose.

 

    Operation of Motion detection

A PIR sensor can detect change in the amount of infrared radiation impinging upon it, which varies depending on the temperature and surface characteristics of the object in the sensor.

When an object, such as a person , passes in front of the background, such as a wall, the temperature at that point in the sensor's field of view will rise from room temperature to body temperature , and then again. The sensor converts the resulting change in the incoming infrared  radiation into a change in the output voltage, and this triggers the detection. 

Objects of similar temperature but different surface characteristic may also have a different infrared emission pattern, and thus moving them with respect to the background may trigger the detector as well.