Explanation Of PIR Sensor And Motion Detection

In physics, motion is a change in position of an object with respect to time and its reference point. A sensor is a convertor that measure a physical quantity and convert it into signal. now, there are two basic types of motion sensors : active sensors and passive sensors. active sensors emit signal, typically light or sound waves which is reflected back by the surrounding. and then the reflected signal is received by the sensor and being measured.

On the other hand, a passive sensor is a device that do not emit a signal, but instead detects and responds to some type of input from the physical environment. and we will see that the PIR sensor is actually a passive sensor.

Passive Infrared Sensor (PIR sensor) is an electronic device that measure infrared (IR) light radiation from objects in its field of view, usually it is around 110 degree.

Motion is detected when an infrared source with one temperature (such as human) passes in front of another infrared source, with another temperature, that means when a human or animal body will get in the range of the sensor. it will detect a movement because the human or animal body emits heat energy in a form of infrared radiation. and usually it is between 3 to 7 meters based on the module you are using right now.

Now the term passive means that the PIR device does not emit an infrared light but, passively accepts incoming infrared radiation from the environment. now for many basic projects or products we may to detect when a person has left or entered the area, and PIR sensors are great as they can detect whether a human has moved in or out of the sensors range. and also it is worth to mention that it is very low cost module.

The module has just three pins, a Ground and a VCC for powering the module, and an output pin which provides high logic level if an object is detected, also it has two potentiometers, one for adjusting the sensitivity of the sensor, meaning the distance we would like to measure, and the other for adjusting the time the output signal stays high when object is detected.

You will probably need to check the specific ranges per the module you using right now, for "Sensitivity Adjustment", clockwise (right) will decrease sensitivity and counter-clockwise (left) will increase sensitivity. The goes with "Time Delay Adjustment",

We can decide how long the output of the PIR sensor module will remain high after detecting a motion, range is usually between 3 seconds to five minutes, clockwise – increase delay, counter-clockwise – decrease delay. The last thing we need to know about it is that the PIR sensor requires a warm-up time in order to function properly.

This is due to the setting time involved in “learning” its environment. it is recommend to add a delay time in the setup function. When the module is operating, in case of motion being detected the sensor will output HIGH signal, for a period of time based on the manual, adjustment using the time delay potentiometer.

now we will see how exactly we are using this sensor in our circuit, how exactly we are creating the sketch needed to operate that sensor.