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>it is HC sR-501</p>
<p>my pir sensor is giving so random output. E.g. i have connected one LED with load of 220ohms and it is giving me output so anonymous like LED glows for some time then after shuts off and again after some times it glows with out any motion in front of the PIR sensor. I dont understand what ids the problem? can you help.</p>
<p>how to combination 4 pir sensor sir? please help</p>
<p>Would a PIR sensor still work if it was attached to a moving object?</p>
<p>Hey! can the PIR sensor also detect a bird?</p>
<p>Not sure it originated here but take a look at this URL: </p><p>http://www.glolab.com/pirparts/infrared.html</p>
<p>I used the PIR sensor to light on led lights at night if I need to go to my kitchen for some water or the toilet without switching on the normal lights. I connected the PIR sensor to an arduino mini (5v) with a light sensor and 2 leds. The light sensor stops the leds being turned on in daylight. I powered it all with an old nokia mobile charger. Really usefull project.</p>
would u like to send me the complete instruction of your project my email address is kirbyimalagayo@yahoo.com
would u like to send me the complete instruction of your project my email address is nnn9452@gmail.com
<p>would u like to send me the complete instruction of your project my email address is nnn9452@gmail.com</p>
<p>Hey Keep27,</p><p>I want to do something similar with two PIR sensors and a daylight sensor. My project will be modifying a 12v camper porch light with this idea. I will be using a 12v LED bulb in place of the incandescent. Do you have any links you could share with me so I can learn how to do this? My concern is the 12v supply and these sensors are saying 5v. So I need a regulator to step this down I suspect. I continue my search for a good source for a diagram on how a circuit like this could be wired up, any help is appreciated.</p>
<p>Ah looks like my best bet is to use a transistor to switch the 12v on and off to the light. Next thing I need to figure out is how to add a light sensor in the mix.</p>
<p>Hi crazytimmy. Normally you would use some sort of voltage regulator as I understand it. I salvaged an LM 1117adj from an old router in a different project which I'm also going to connect to a 12V lamp output. Normally people suggest using the LM7805 like in this link: <a href="http://electronics.stackexchange.com/questions/109039/reducing-12v-to-5v" rel="nofollow">http://electronics.stackexchange.com/questions/109...</a> but if you are going to use an arduino mini pro or the equivalent to control the PIR sensors and lightsensor, you can just connect the 12v to raw on the arduino (12V is the max.), gnd to gnd and it will supply an 5v output (unless you have the 3.3 version). As long as you don't exceed the max current of the arduino I don't think you will have a problem.</p>
<p>can I use a 9V battery instead of 5V for PIR?</p>
<p>you bought this for 10$ <a href="http://www.adafruit.com/index.php?main_page=product_info&cPath=35&products_id=189" rel="nofollow">at the Adafruit shop</a> i bought it for about 1.5$ in my country</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>Somewhat similar problem - My sensor detects even there is NO movement. So I changed the pots so that it lowers sensitivity. no help.</p>
<p>Hey, did you find a solution? I have the exact same problem. No matter what tutorial I follow, it always ends up staying at GPIO = HIGH. As in, it is always detecting movement, even though nothing is moving near it.</p>
<p>what worked for me is to make sure my ground was also connected to the arduino. the arduino and pir have to have a common ground.</p>
<p>I have a small trick - If I wave the tip of the screwdriver in between the potentiometers slightly -then I see some motion detected activity. That's not acceptable -but it works for my demo purposes.</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>
Same problem and sensor can only get it to turn off after a minute under a box.
<p>how can i detect the written text or data using motion sensor? Or is there any sensor to serve the purpose of recording the text written</p>
<p>The 'resolution' of the sensor/ lens combo here is WAY too low for what you need. It's pyroelectric so detects thermal energy NOT. Your needs won't be served by a simple electronics project, you'll need a good lens, a great sensor, loads of light and a processor to handle all the data and recognise text. A modern smartphone can do it in real time and even translate it to another language but that costs a lot more than a &pound;1 PIR sensor, an LED and a few wires :)</p>
<p>Sorry *NOT light* that should read.</p>
<p>The 'resolution' of the sensor/ lens combo here is WAY too low for what you need. It's pyroelectric so detects thermal energy NOT. Your needs won't be served by a simple electronics project, you'll need a good lens, a great sensor, loads of light and a processor to handle all the data and recognise text. A modern smartphone can do it in real time and even translate it to another language but that costs a lot more than a &pound;1 PIR sensor, an LED and a few wires :)</p>
<p>would u like to send me the complete instruction of your project my email niazmarshed@gmail.com</p>
<p>Can PIR sensors make the distinction between sizes of objects? Ie Could it tell if it was water or a solid going past it. Thanks.</p>
Do you have an instructable of how to drive a 3v relay module with a PIR with no controller? I have tried but it appears the PIR does not supply enough voltage.
<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 fine. May be it is due to movement sense it may very</p>
<p>MY PIR sensor is being detecting continuously even with movement. What to do?</p>
<p>Hello, can anybody please help me with this? I was wondering if there was some sort of filter that I could place in front of the pir module, that would filter out any low temperature objects and only allow high temperatures to trigger the sensor (body heat). I plan to mount the sensor on a rotating turret, and when it spins I don't want the sensors to be triggered by the moving background (walls, bookshelves, etc.) thanks.</p>
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:)

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