How to integrate PIR with Arduino.Human Body Sensor Vendor

　　Step 1: What is a PIR sensor?

　　Passive infrared sensor is a kind of object detection sensor. There are two types of object detection sensors

　　Objects have sensors and proximity sensors that require magnetic fields, ultrasonic or infrared radiation from active sources. Passive infrared sensors do not require any such source and respond passively to heat radiated from the detected object.

　　Step 2: What does PIR do?

　　Passive infrared motion sensors commonly referred to as PIR detect blackbody radiation, which all objects emit according to their temperature relative to absolute zero temperature. The sensor responds to infrared radiation centered at 10μm (10 microns or 10,000 nm). This is the approximate body temperature of humans and animals.

　　The "passive" in the term "passive infrared" refers to the behavior of the human body. A detector, which passively receives infrared radiation. Proximity sensors must actively generate their own infrared radiation, which can be disturbed or reflected by nearby objects.

　　Step 3: Schematic notation

　　Step 4: Typical application of PIR

　　1) Motion-sensitive outdoor lighting is almost always PIR based. Similarly, when a PIR indicates human activity, the security system may sound an alarm or activate a camera.

　　2) The wildlife surveillance system uses PIR to start the camera, which can then run for preset time intervals.

　　3) A car warning system has been developed that uses backward PIR to detect pedestrians.

　　4) Industrial indoor lighting may use PIR, which automatically turns the lights on when people enter the room, and then turns the lights off (after a certain delay) when people are no longer detected in the room. The goal is to prevent wasted energy when employees forget to turn off lights.

　　Step 5: How PIR works

　　A PIR module contains multiple components. The most visible is an array of at least 15 small lenses that focus infrared light from the environmental region onto a thermoelectric detector, also known as a thermoelectric sensor. The response of the detector is processed by an amplifier so that the signal can trigger either an electromechanical relay or a solid-state relay. This relay operates external equipment, such as lights or alarms.

　　Additional circuitry may be required to allow the user to control the sensitivity of the PIR module and how long the relay remains closed. The user can also set the time when the PIR is active, or another phototransistor can turn the PIR off during the day. If a phototransistor is included, the sensitivity is adjustable.

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