PIR and circuit load, i.e. voltage drop, -> false positive

Hi,

I’ve some of these PIR and encountered strange false positive motion detection. In most of my projects, I feed 3.3V directly through the “repeat trigger high” pin.

I tested two setups to find the cause:

  1. 5V through the Vcc pin
  2. 3.3V through “repeat trigger high” pin. Power supply through AMS1117-33 and HT7333, respectively.

Both circuits work 100% stable when nothing else happens (left schematic).
When I add an LED to the circuit (see right schematic), each time the button is pushed the PIR data pin goes HIGH for setup 2. Setup 1 is still stable/reliable.

PIR.png

I have no oscilloscope but I measured the voltage. My DMM showed a voltage drop from 3.31V to 3.30V. I added a capacitors (470 µF). No measurable voltage drop but PIR is still triggered.

Any idea how to stabilize it?

Thanks & Best

Do you have documentation on that board? a picture is ok, but it doesn't tell you what you need to know.

I think you need to supply power to VCC and move a jumper to select re-trigger or not.

terraduino: In most of my projects, I feed 3.3V directly through the "repeat trigger high" pin.

BISS0001 datasheet can be found online. I assume you leave the jumper in the re-triggerable (VCC) position (so pin1 is not "floating), and feed 3.3volt supply to that same point. PIR sensors are very sensitive devices, and the onboard 3.3volt regulator is there for isolation. If you must power it from 3.3volt, try an RC filter. e.g. 100ohm between 3.3volt supply and PIR supply, with a 470uF (or more) cap from PIR supply to PIR ground. Leo..

Thank you both for your feedback.
The jumper is set like on the picture and my 3.3V regulated power is connected to “H”.

@Wawa I’m not quite sure how you meant the RC filter. I’ve added the RC low pass(?) filter to the schematics. Maybe you can confirm that it’s like you meant it.
PIRn.png
I’ve already tested it. Seems to be better now.

I read about low pass filter and I’m now wondering how I could adjust it to get a “stronger” effect? But as far as I understand it depends on the oscillation of the voltage drop, which I don’t know and cannot measure.

Thanks & best

RC filter is connected right.

Increase cap value if you want a stronger effect. Leo..

Thanks a lot!