best way to connect PIR sensors

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,
I am using 10 PIR sensors with an Arduino Mega. Now I am doing some test with 2 sensors.
I followed the standard schematic:

  • "5V" pin on arduino to Vin for sensor
  • "Gnd" to "Gnd"
  • Resistor between "5V" of arduino and alarm pin of sensor
  • Wire from alarm pin to input pin on arduino

but I get unstable values when there is a movement: a lot of "1->0" transitions instead of one per movement.
Then I saw this post
http://www.sparkfun.com/commerce/account.php?id=74877
where there is the same problem using the "5 V" pin, so I tried
the VIN pin of the Arduino mega (the Arduino mega is powered by USB) instead of the "5V" pin. Now I obtain stable values (one 1->0 transition per movement).
Summarizing now I use:

  • "Vin" on arduino to Vin for sensor
  • "Gnd" to "Gnd"
  • Resistor between "Vin" of arduino and alarm pin of sensor
  • Wire from alarm pin to input pin on arduino
    Someone could give me some suggestions/explanations of this behavior?

Thanks a lot

2

Someone could give me some suggestions/explanations of this behavior?

Simple the data sheet says it needs 12V so it is no surprise if it doesn't work correctly when you only give it 5V. That's what data sheets are for.