Let's Make Robots!

PIR (Passive Infrared Sensor)

Vendor's Description: 

PIR's are cheap little things that combined with a little chip (PIR Sensor Control IC) and possible a Fresnel Lens will tell you if there is motion in font of it. Especially that of a human body, as it is reacting on Infra Red.

You can not use a PIR for anything but on something that stands still, to detect something else that moves.

No, you cannot use a PIR to make a robot follow you. The PIR only detects changes. A moving robot (even turning it's head) would be one constant "alarm" of "changes" - not possible to tell what is what.

If you want to make a robot follow you, you either have to use a camera and some serious calculations, or something like the devantech Thermopile array sensors or hack an Infrared thermometer (often refered to as a Laser thermometer asthey often come with a guiding laser-beam).. or something else :D

PIR's can only detect changes! A moving robot will detect changes all the time! 


Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Sounds like these would be great for doing a robot guard dog that just sits and waits for someone to break in and then activates itself, powers on the chainsaw and starts to chase to burglar (using some other form of tracking)!
that sounds like a great idea only if i could tell between a robber and you... sounds like fun tho

haha, yes it would be nice not having the robot going berserk on one self :-D.

I took a PIR sensor from an old alarm system. If you leave it in the device I agree you could only use it while still. However I took the actural sensor and I think you could get some kind of tracking with it. I used 4 NPN transistors and a lot of resistors to get an amplifided signal but that signal is around 2.5V when it sees nothing. If there is something to the right of it, it drops the voltage a varing amound depending on how much it sees. If there is something to the left the voltage increases. It seems like you could put something together to track someone.

It sounds like there are some active components in Frit's sensor that you've removed. I understood that there was only and output it whatever was in front of the sensor "changed".

I hope you're right. A scanning (YDM-style) PIR head would be something else. I'm hoping that the voltage you're seeing is proportional to the heat of the subject.

Please persue this aggressively, and keep us posted at every turn!


I have two of the alarm systems. One I tore apart for the sensor (it looks like the one pictured above but without any text). And the other one still works as it should, apply 12V if it sees something is opens a relay. The boards have an amplifier and 4 comparitors. Part NO. LM358M and LM339M. I am going to play with the still working one as I can easily get to the amplifided signal.

 The funny part is the sensor runs off 5V not 12V. It is regulated on the board. That makes it easier to use with a microcontroller. 

 I need to find a better amplifier as the signal from the sensor it self is extreamly small, 0.55v-0.62V about. With the transistors I got it to go from 0-5V but it is not that great. I will post more when I know more.


 EDIT: See http://www.youtube.com/watch?v=8ahlIXnmqbQ for a sample of it's output.


I don't know about plastics, but IR doesn't pass through glass.  So if the fresnel lens is glass based (which I guess is rare nowadays), your suggestion wouldn't work.  Anybody know about plastics?
You can buy fresnel lens that are made of plastic that are transparent to IR. I have two. The plastic on a TV remote looks black but it is transpartent to IR.

As I am trying to tell everybody, the PIR's are only good for detecting changes.

Every motion detector out there has fresnel lenses over them for that very reason; To get as much attention to changes as possible, because the PIR is actually a quite dumb little thing, and needs lots of amplification, and dual-runs etc.

These fresnels are made specially to have lots of focus areas, and not as what is else wise known as a fresnel: a "flat magnifying glass". The ones used for PIR's are made to amplify changes:


But our friend seems to have stripped teh IR sensor out of the PIR sensor. I'm hoping that he signal he's seeing is proportional to the heat in front of the sensor. What he has is no longer a PIR. Perhaps it will only see "heat" or "no heat" but either way, a scanning head would be able to say "Oh, there's heat. Now it's gone. Oh, there it is again. It's moved a bit."

Even if the PIR was used and it only detected changes, I don't see why the scanning head couldn't say "Oh, there's a change. Oh, there's another one in a different place."

Surely that's what the ultrasonic scanning head does? Sure, it measures distance, but it would work just as well by detecting the "edge" change between a near object and a far object.

I'm keeping my mind open and my fingers crossed.