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A New Chapter for MagicMirror: The Community Takes the Lead
Read the statement by Michael Teeuw here.

PIR Sensor: false positive detections

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  • F Offline
    Fozi Project Sponsor @MZ-BER
    last edited by Nov 22, 2021, 12:31 PM

    @mz-ber said in PIR Sensor: false positive detections:

    HC-SR501 PIR

    I’m with @Stefan723. I had used MMM-NewPIR in the past but switched back to MMM-PIR-Sensor again for reasons. MMM-PIR-Sensor is simple, robust and does the job reliably. May be you have some intereferences, too, which trigger false positives.
    Due to the proximity of the Vout and GND wires to the WLAN module, unwanted interferences may occur which might prevent the PIR sensor to switch from high (motion detected) to low state (no motion detected). The wires work like an antenna in that case. As a result, the display will stay on. A ferrite bead attached to those wires, e.g. taken from an old VGA cable, reduces the interferences and allows for correct state change.

    Hope that helps.

    HowTo: Replace PIR Sensor with a RCWL-0516 Microwave Sensor

    Z 1 Reply Last reply Nov 22, 2021, 1:01 PM Reply Quote 0
    • Z Offline
      Zoltan @Fozi
      last edited by Nov 22, 2021, 1:01 PM

      @fozi I also had false triggers. It turned out that my PIR was too close to my Pi and the WiFi chip induced EMF into the PIR. By moving the PIR further away and introducing a low pass filter i solved my issue. Have a look at my circuit and comments

      https://forum.magicmirror.builders/topic/15458/smartmirror-dashboard

      F M 2 Replies Last reply Nov 22, 2021, 3:12 PM Reply Quote 0
      • F Offline
        Fozi Project Sponsor @Zoltan
        last edited by Nov 22, 2021, 3:12 PM

        @zoltan Really nice build!Congrats!
        Yeah, a low-pass filter can solve the interferences from the WiFi module, too, of course. But due to my lazyness and impatience I sacrificed an old VGA cable and re-used the ferrite bead:beaming_face_with_smiling_eyes:

        HowTo: Replace PIR Sensor with a RCWL-0516 Microwave Sensor

        1 Reply Last reply Reply Quote 0
        • M Offline
          MZ-BER
          last edited by Nov 22, 2021, 3:17 PM

          Hey folks - thanks for your answers. I decided to goahed with a RCWL-0516. But have the same issues. I’m testing the sensitivity with a python script. I also covered it in alu foil - no change. Now I ordered a ferrite beat and will add to the cables (around all of the them or only GND, 5v or Output?)

          I’m also thinking about adding a low pass filter, but I have no experience with that. Where do I have to add that? GND & Output?

          F 1 Reply Last reply Nov 22, 2021, 3:25 PM Reply Quote 0
          • F Offline
            Fozi Project Sponsor @MZ-BER
            last edited by Nov 22, 2021, 3:25 PM

            @mz-ber Just put all wires through the bead.
            With the RCWL-0516 you should note that they can be very sensitive (up to 7m on free sight) and detect motion even through walls. First I went the alu foil route, too, but then modded my RCWL-0516 with a trimmer. Now the mirror is triggered when I approach the mirror less than 1m. Check the link in my signature for details, if you like.

            HowTo: Replace PIR Sensor with a RCWL-0516 Microwave Sensor

            M 1 Reply Last reply Nov 22, 2021, 4:39 PM Reply Quote 0
            • M Offline
              MZ-BER @Fozi
              last edited by Nov 22, 2021, 4:39 PM

              @fozi Yes! I followed your instructions in detail - that was very helpful. And yes, I noticed how sensitive it is. In your tutorial you removed the the tiny SMD resistor soldered and replaced that. What if I just remove it and not replace it. Is the range than completely gone and doesent work anymore?

              F 1 Reply Last reply Nov 22, 2021, 6:00 PM Reply Quote 0
              • M Offline
                MZ-BER @Zoltan
                last edited by MZ-BER Nov 22, 2021, 6:52 PM Nov 22, 2021, 4:49 PM

                Hi @zoltan - I was reviewing your tutorial. Really good documented. I have a question about the wiring drawing you shared. I’m new to it and dont understand everything. But I’m a fast learner :-)

                In your drawing you added a couple of symbols. I guess these are resistors and filters, right?

                Numbers 1, 2 and 3 look similar, only with a diffrent capacity. Is that a Capacitor?
                What are 4 and 5? Is that a conductor? What capacity is here needed?
                And number 6, not sure. Is that a RND or a resistor?

                592b9840-5b90-4d92-9bd3-b79a1f1176ad-image.png

                Z 2 Replies Last reply Dec 3, 2021, 4:00 PM Reply Quote 0
                • F Offline
                  Fozi Project Sponsor @MZ-BER
                  last edited by Nov 22, 2021, 6:00 PM

                  @mz-ber If you remove the resistor completely without any replacement the sensor won’t work any more.

                  HowTo: Replace PIR Sensor with a RCWL-0516 Microwave Sensor

                  1 Reply Last reply Reply Quote 0
                  • T Offline
                    thgmirror
                    last edited by thgmirror Nov 22, 2021, 6:02 PM Nov 22, 2021, 6:01 PM

                    Didn’t I said, I’m not an electrician?
                    It is not a step-down/up … it is called Pull-Up, resp Pull-Down.
                    Please see here for detailed (german) explanation: https://www.elektronik-kompendium.de/sites/raspberry-pi/2006051.htm

                    M F 2 Replies Last reply Nov 22, 2021, 6:50 PM Reply Quote 1
                    • M Offline
                      MZ-BER @thgmirror
                      last edited by Nov 22, 2021, 6:50 PM

                      @thgmirror Yep, that is what I’ll do next. Already ordered a starter kit with resistors, inductors and capacitors.

                      I also noticed, even if I added the ferrite beat, that the sensor recevied every minute excact on the second a signal

                      c06e06b8-0380-4a64-a040-2ef29f7c68ee-image.png

                      1 Reply Last reply Reply Quote 0
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