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Insight - Learn the Working of a Motion Sensor or PIR Sensor

Table of Contents:

Written By: 

Abhimanyu Mathur

The modern world is filled with gadgets that get excited when they sense human motion. Automatic doors in elevators and shopping malls, burglar alarms at houses and shops, automatic lighting systems, electronic amenities in washrooms are just a few examples where human presence or absence puts the device into active or passive state.  Smart, right? Now, what if we tell you that behind this smart response to motion is a gizmo that does not even reach the 2cm mark in size. Known as Pyroelectric or Passive Infrared Sensor (PIR, in both cases), this small electronic device is the curious case for this Insight.



Every object that has a temperature above perfect zero emits thermal energy (heat) in form of radiation. We, Homo sapiens, radiate at wavelength of 9-10micrometers all time of the day. The PIR sensors are tuned to detect this IR wavelength which only emanates when a human being arrives in their proximity. The term “pyroelectricity” means: heat that generates electricity (here, an electric signal of small amplitude).  Since these sensors do not have an infrared source of their own, they are also termed as passive.


How does PIR sensor selectively responds to human radiated IRs? Upto what range can this sensor work? What lies inside this sensor that makes it work? This and answers to more questions in this Insight on PIR sensors. What adds more charm to this Insight is that the Panasonic 10m sensor taken is also one of the smallest PIR sensors commercially available till date.

Motion Sensors




I think this is best website for embedded system. 




Arun Yadav

How PIR sensor input is connected to 8051 microcontroller to run the stepper motor...?

Please suggest me some programs in embedded c or assembly language to run stepper clockwise and anti clockwise with variable time delay......plz help me

thanx alot ....this post is very helpful.....can u tell the prize of dis sensor...

Pir sensor is about Rs.100 per piece

very useful site.i was learn so much information form this website. thanks u very much

is this PIR sensor can be used for human following trolly??


is PIR sensor can be used for  motors shaft movement detection?????