Pyroelectric ("Passive") InfraRed sensors:

'''What is a PIR sensor?'''

PIR sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range. They are small, inexpensive, low-power, easy to use and don't wear out. For that reason they are commonly found in appliances and gadgets used in homes or businesses. They are often referred to as PIR, "Passive Infrared", "Pyroelectric", or "IR motion" sensors.

PIRs are basically made of a pyroelectric sensor (which you can see above as the round metal can with a rectangular crystal in the center), which can detect levels of infrared radiation. Everything emits some low level radiation, and the hotter something is, the more radiation is emitted. The sensor in a motion detector is actually split in two halves. The reason for that is that we are looking to detect motion (change) not average IR levels. The two halves are wired up so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low.

Along with the pyroelectic sensor is a bunch of supporting circuitry, resistors and capacitors. It seems that most small hobbyist sensors use the BISS0001 ("Micro Power PIR Motion Detector IC"), undoubtedly a very inexpensive chip. This chip takes the output of the sensor and does some minor processing on it to emit a digital output pulse from the analog sensor.

For many basic projects or products that need to detect when a person has left or entered the area, or has approached, PIR sensors are great. They are low power and low cost, pretty rugged, have a wide lens range, and are easy to interface with. Note that PIRs won't tell you how many people are around or how close they are to the sensor, the lens is often fixed to a certain sweep and distance (although it can be hacked somewhere) and they are also sometimes set off by house pets. Experimentation is key!

Some basic stats

These stats are for the PIR sensor in the Adafruit shop which is very much like the Parallax one. Nearly all PIRs will have slightly different specifications, although they all pretty much work the same. If there's a datasheet, you'll want to refer to it

More links!

Step 1: How does it work?

PIR sensors are more complicated than many of the other sensors explained in these tutorials (like photocells, FSRs and tilt switches) because there are multiple variables that affect the sensors input and output. To begin explaining how a basic sensor works, we'll use the rather nice diagram below (if anyone knows where it originates plz let me know).

The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR. The lens used here is not really doing much and so we see that the two slots can 'see' out past some distance (basically the sensitivity of the sensor). When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor, which causes a positive differential change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected.

The PIR sensor itself

The IR sensor itself is housed in a hermetically sealed metal can to improve noise/temperature/humidity immunity. There is a window made of IR-transmissive material (typically coated silicon since that is very easy to come by) that protects the sensing element. Behind the window are the two balanced sensors.

Check out the images for more details:
<p>Hey! can the PIR sensor also detect a bird?</p>
<p>hi i am using PIR for last 2 months..Now i measured the output voltage and found it is 3.1 volt. (u said its 3.3v) Is my PIR is dead...or is working fine.? plz help </p>
<p>its not working for me. when i plug everything in and upload the sketch the led comes on and stays on. in the serial monitor it says motion detected. my pir does not have a jumper on the back but it does have three pads. there is 2 pots on it and i tried adjusting them but it didnt seem to help. i got the pir on ebay (http://tinyurl.com/led58rm) if any one can help that would be great</p>
<p>In the data sheet the pins you have marked are used to set the trigger in either single or repeat modes. I tried using the system in single trigger mode by soldering the 1st and 2nd pins but it seemed to heat up the system. I then soldered the 2nd and 3rd pins(Circled in Red) and it worked all right.</p>
<p>ok i may try soldering them together and see what happens. :) </p>
<p>Somewhat similar problem - My sensor detects even there is NO movement. So I changed the pots so that it lowers sensitivity. no help.</p>
Same problem and sensor can only get it to turn off after a minute under a box.
how to if i want used 3 PIR for the sensor?
<p>I have python code that monitors multiple sensors on my page.</p><p>http://tigermountainsprings.net/wp/index.php/6-pir-infrared-sensors-and-the-coop/</p>
<p>please how can i connect it to a loud alarm and an halogen bulb?</p>
<p>Can i adjust the range to be 0.5 feet not 20 ? or it's fixed .</p>
<p>What does it mean if the LED is flashing at a very regular interval? Almost like it's on a timer? It's not random. </p>
<p>Excellent tutorial!!</p><p>Hats-off</p>
<p>If still required, Pictures in Step 1 is from the &quot;Infrared Parts Manual&quot; by &quot;GLOLAB corporation&quot;. Hope this helps :)</p><p>http://www.bucek.name/pdf/re200b.pdf</p>
<p>If you want to make your own wireless PIR sensor, try out MySensors motion sensor example:<br><a href="http://www.mysensors.org/build/motion" rel="nofollow">http://www.mysensors.org/build/motion</a></p><p>Arduino library on Github:<br><a href="https://github.com/mysensors/" rel="nofollow">https://github.com/mysensors/</a></p>
<p>How to connect two PIR sensor in one circuit which connected with one light??? If i cross either of the sensor means the single light which is connected to the circuit should glow.</p>
<p>Very nice tutorial! Just want to share this place where you can get the HC-SR501 PIR sensor for cheap: <a href="http://voltatek.com/en/sensors/69-motion-sensor-module-hc-sr501-pyroelectric-ir-infrared-adjustable.html" rel="nofollow"> http://voltatek.com/en/sensors/69-motion-sensor-m...</a></p>
When testing, is the resistor necessary?
<p>..the resistor is needed for testing with LED (to limit the current)</p>
what if i would like to turn on a relay when trigger? <br> <br>thanks! <br>marC:)
<p>buy this </p><p><a href="http://www.ebay.ca/itm/310566336050?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649" rel="nofollow">http://www.ebay.ca/itm/310566336050?ssPageName=STR...</a><br><br>very easy to use</p>
What would i have to do so that it alerts my phone when motion is detected?
<p>gsm shield and a activated sim card and some electronic basic supply</p>
How much current can the module deliver to the output? <br> <br>Great write up. Thanks.
<p>not really, he copy and pasted it from the website he linked.</p>
Hey there guys, i would just like to know does the PIR motion works with other programming such as C programming and such. Another thing is, is it possible to do this: <br>When sensor detects, LED lights up <br>When sensor x detect, LED would dim instead of off. <br>Thanks. Your reply would be highly appreciated. <br>
<p>I actually just posted an Instructable recently that essentially does what you are asking. Only thing you would have to change in the code is the PWM value in the analogWrite() function from 0 (which is totally off) to 50 or so (which would make the LED shine dimly). </p>
WOW! Thanks for this tutorial!! I love it! Thanks for doing this!!! 11 thumbs out of 10!!! :-) <br>
Hi, <br>I would like to know if PIR sensor can tell me that the person in range is moving toward to the left or right? Is it possible or I need something else to detect? <br> <br>Thanks!
Are you still selling the sensors on your website?
hi We sell this PIR sensor my web is http://en.nysenba.com and my email is lily@sbcds.com
@mhaziq <br> <br>Yes, it is possible to dim the LED upon detection.
Great tutorial. I am looking for tutorial where i can turn on some kind of camera with motion sensor and arduino. Rurn it on,record some video or take a few pics and turn camera off. i am very new in programming and arduino. Can you give some advice where can i find something similar, please!
How would you increase the sensitivity of the PIR sensor using Arduino? (using code) <br>I'm doing a project, and coding in Arduino.
I'm going to use one of these to detect opponents in air-soft wars. Is there any material that i can cover the sensor with to protect it from BBs but will still allow IR light through?
A 1/4 piece of Lexan (polycarbonate) should do the trick. You can heat form it to fit the pir using an automotive soldering iron and a suitable metal form. It's a tricky thing to do, so practice in an open area, being wary of overheating the lexan, of any fumes, and of starting a fire.
is it possible to change the LED into a servo, and if it is what other changes do i have to do? thank you...
can we use this PIR sensor at night, for example, a remote area with no road street lights. please reply...thank you..
This detector can detect a car? For example, a car on the road. I make a mini project on road safety. I want to put this sensor to detect the car. Will it be applied? I just want to find out.
gr8 tutorial.. got one of these for 2 $<br>
i did this step and it doesn't work :( ideas???
Some more info here on using these with Arduino:<br>http://arduino-info.wikispaces.com/Brick-Pushbuttons%26OtherSwitches#Motion
I have just the sensor (TO9 can package) itself. A PIR D203S. The datasheet tells me how to hook it up: 5V, Gnd and Signal (it is an analog device). But it tells me very little about the signal I will be getting. Short of dragging out my O-scope and doing the testing; do you know what type of signal I should expect? This module from LA you use is nice, but I'm using my own uController so I wouldn't get the clean digital signal you show. BTW Wonderful writeup! you would make my old college profs proud.
opps, it a TO-5 package not a TO-9
huh, got 10 of these super cheep from my school used, now i actually know what they do!
PIRs are great - it is quite easy to connect a PIR and LED (strip, bar, rope, single LED, etc) to a battery and provide light, when needed, to a closet, cupboard, drawer, stairway, hallway, room, etc.<br><br>Or instead of the LED connect to an activator of some kind - its great they price has dropped and the they are available as a 'component'.<br><br>We have an excellent factory making them here.
10USD seems a bit high, as I can source locally for under 5USD. <br><br>Two models in 3 versions;<br><br> w or w/o photocell - 3 to 5V or 5 to 12V - fixed sensitivity<br><br> w or w/o photocell - 3 to 5V or 5 to 12V - adjustable sensitivity<br><br>The output can be 3+V (for most digital logic) or Open-collector (solid state switch).
Great info. I always wondered if you could take the lens/globe off. (looks like not a good idea)

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