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Hello, I bought a PIR Motion Sensor (this one http://www.robot-italy.com/product_info.php?products_id=1558).
I followed the schema reported in the posted url, but it does not work, it gives me values not consistent with the movements.
I am not so good in electronics, so I don't know how to proceed.

The signal produced by the PIR is 0V when there is no motion, and 12V when some motion is sensed.
I also tried to connect the signal produced with a series of two resistors: 14Kohm and 10Kohm. And then to the ground. In this way, the potential difference between the 10Kohm resistor and the ground should be 5 volts when some motion is sensed. Anyway it does not work!

Can anyone help me?

Thanks a lot!


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Hi what kind of signal do you expect?
And what signals do you get?

google translate tells me this:
"If movement is detected inside the room, the pin labeled "alarm" goes to logic low."

why do you think it would output 12V?

In the schematic its attached to 5V not 12V on the signal line, so it should either output 5V or 0V.
IMHO the sensor doesnt output anything, it just switches to gnd

Open collector:
An open collector is a common type of output found on many integrated circuits (IC). Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized (open) on a pin of the IC. The emitter of the transistor is connected internally to the ground pin

Do u actually source the sensor with 7V-12V?
« Last Edit: July 06, 2012, 05:04:14 am by lax123 » Logged

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it seems to work also with 5V

check this out:

http://bildr.org/2011/06/pir_arduino/
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Yes, I tried also the example in the link, but it gives me "Motion Detected" also when there is no motion.

The PIR is connected to a 12V power supply.

You're right, connecting a multimeter to the signal wire with the ground on the same ground of the 12V power supply, it is shown 12V when no motion is sensed, and it goes to 0V when a motion is sensed.

Yes, in the circuit in the figure they connect 5V to the resistor and then to the signal, but it simply doesn't work.

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i didnt have one yet, but from my understanding that motion detector is rather a heatsensor then an actual motionsensor. If the 2 heatsensors inside measure a different value u get a signal.
Did you consider that?
Do you get a Motion detected while letting it face a cold wall and wait for like a minute?

found this:
"I had the same issue with this Sparkfun PIR. I resolved it by wiring past the voltage regulator and running it off of the Arduino 3.3v"
and why do you use 12v when u can use arduino power?
« Last Edit: July 06, 2012, 05:39:48 am by lax123 » Logged

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mmm...Ok, maybe it's a problem like that one, but I only have it on my desk....
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