Introduction: 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.

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.