Prepare Some Surplus PIR Sensors for Robotics




I found a bunch of PIR sensors on eBay. They are mounted on a pcb that was produced for a hands free set for mobile phones. I like to describe here how to prepare the sensor for the usage in robotics projects.

If you don't know what a PIR sensor is, just have a look at Wikipedia . The product where the boards comes from can be bought here . I bought the boards from a seller named "kalleb" on eBay. A search of the seller or for the subject "PIR INFRARED SENSOR" leads to the offer. He still offers some boards.

On the boards you can also find some switching voltage converters. I used them in an other project where I needed to get +-15V out of a +5V supply. There are other useful components as well, but here we only need the pir sensor and the op amp that prepare the pir signal for direct usage with a microprocessor.

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Step 1: What You Need

First of all you need the pir board.

for preparation:
- a soldering iron
- tin-solder
- a jigsaw

for testing:
- a tabletop power supply with a +5V output (0.2A current is enough for testing)
- a voltage meter
- some wires

Step 2: Cut the Pir Sensor From the Board

We need only the pir sensor and the electronic that prepares the sensors signal for the usage with a microprocessor. The sensor and the electronic is working fine, it only requires single +5V supply and it delivers a signal that can be feed into a microprocessor. Therefore it makes sense not to desolder the sensor and create all the stuff by yourself.

Just cut the piece of pcb out that you need.

There is a "save" cut that you can find on the picture, drawn as a red line. If you cut there everything will work fine after cutting. You also get some nice mounting holes. If you need to save space, or weight, you can cut along the yellow line. If you do so you will also cut a wire that carries +5V between the pir sensor and the op amp. The wire runs inside the pcb. It seems to be four layer pcb. This is no problem if you just replace it with a small wire that you solder on the pin of the pir sensor and pin 8 of the op amp.

Step 3: Testing

For testing you need to add wires for the power and a wire that carries the output signal.
Put +5V on on the board and connect a voltage meter to the output pin.
Moving you hand near the sensor leads to a +5V pulse on the voltage meter. If you keep your hand still the voltage drops. If you move you hand the voltage raises. The module gives signal for the moving.

This works with every object that emits infrared radiation. The module gives a pulse when it detects a difference in the infrared radiation of the objects it points to. I tested with my human body, with heated objects, like soldering irons and even with a plastic ruler. All these things where detected. Some where detected far away from the detector and some if the object war near by the detector.

I did some testing with the device.
I found out that it works from about 25cm down to nearly 0cm. At 25 cm it detects big sources, like people. A single hand of a person is detected at about 10cm distance. If I take a soldering iron witch is heated at about 350 degrees Celsius, it is detected at 25cm.
A plastic rules is detected at 5cm. A screwdriver at about the same distance.

The detector gives pulses on the difference of the infrared radiation it "sees" ... that makes me think that also ice cubes could be detected. But they don't. Do I follow the wrong theory? ;-)

I think the sensitivity could be enhanced using optical lenses. Household movement detectors use Fresnel lenses to define an area for detection.

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    8 Discussions


    6 years ago on Step 3

    This is very interesting information. I've been building my robot for some time now and this has certainly opened some new paths. Thank you for posting it.


    I got one of these FREE, yes FREE from my school caretaker and the old controller board because we had the alarm replaced.


    11 years ago on Introduction

    Great info! I've been looking for an inexpensive way to do just this.

    If you try optical lenses, make sure that they're transparent in the mid-IR that these sensors see. Glass isn't. Plastic lenses from a disposable camera might be, but I haven't checked. The polyethylene used to make the Fresnel lenses is, of course.

    I'm considering buying a bunch of bare PIR sensors from Goldmine Electronics ( Assuming the part is what they say it is, it comes with a transistor preamp. Building an array of these, with some tiny op amps might make a nice lo-res camera!

    1 reply

    Reply 11 years ago on Introduction

    Hi, I had a look at the sensors you are going to buy. As far as I understand it, this sensor need electronics to get a signal that can be used with microcontrollers. Every sensor I saw so far has a FET transistor build in. But that does not mean that you get a usable signal out of it.
    You can use the schematic I send here to build a working sensor, but you have to build it on your own.
    Before I bought this small boards I experimented with sensors. The signal that comes straight out of them is very small, only some mV.
    Have a look here to find out how the electronics work.


    11 years ago on Introduction

    AWESOME! I like all stuff like this, and I mean all. Cool Instructable!