How to troubleshoot a pir sensor?

Hello I bought a pir sensor off ebay (SKU 14_B000101941) and I plugged it into a solderless breadboard to test it out. I connected a 3v LED between the output and ground and while it does light up, it does not light up when it senses light, it just turns off every 2 seconds, then every 5 seconds. If there is a simple fix to this problem any advice would be appreciated but if not I am willing to buy a different one.

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andy707076 years ago
I have the same sensor! In order for it to work, you need an NPN transistor on the output (I used 2N3904). You also need to move the jumper across to select the output mode as high, otherwise it will work in reverse. Input should be 5v, it does have an on-board voltage regulator which accepts up to 20v, but I wouldn't recommend going much higher as it heats up which can damage it.
pir.jpg
I also noticed you said the LED does light, try it with the jumper in the other position, and then try changing the sensitivity and timeout pots, but I found it worked best as is anyway. I also noticed it can be unpredictable in a room with many IR sources (mostly lightbulbs). I tried it in a dark room and it works flawlessly, detects every hot object that passes.
iceng6 years ago
PIR responds to body heat not light
It sounds like you wired it to heat up so it would quit and cool down and
resume heat up again.
Just supposition until we see a circuit and what power supply you use.

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thorpenny (author)  iceng6 years ago
No, that's not how I wired it. I wired it so that when the passive infrared sensor senses infrared light (yes, infrared is light, it is just such a low wavelength that human eyes cannot see it) I could see if it would set its output pin to "high" (3.3v). The battery I am using is 12 volts.
pir.gif
iceng thorpenny6 years ago
So is it possibly red and aimed at the pir sensor ?
or does a room light have incandescent output or is sunlight leaking in ?
Your circuit is correct.
Are you sure the device likes to source the LED and not sink it instead ?

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thorpenny (author)  iceng6 years ago
No, it is green, and it is not aimed at the pir sensor. A room light is taken into the "background radiation" with which the pir can distinguish between by only sensing changes in voltage created by a heat emitting object passing in front. I don't know what exactly the pir likes, but there is no sink in this circuit.
iceng thorpenny6 years ago
The people who make this thing ( Parallax ) rate theirs at 3 to 6V only !
Three things left,
  1. Try using yours at 6V at the sensor when working ?
  2. Your sensor could now be bad !
  3. How far is your 6V from the sensor ?  Add a 12V 4.7uF el capacitor at the sensor, perhaps switiching the green LED momentarily wacks it.
Good Luck,
Im empty here.

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