💬 Ikea Molgan Hack


  • Hardware Contributor

    So yesterday my molgan started to constantly trigger, which I think might indicate that the voltage is too low. It has dropped down to 1950mV. I will try it with new batteries later today, but the power consumption still seems to be way too high compared to yours @Yveaux.
    I have removed R17 to disable all leds and I have changed the fuses and used your sketch. Any idea what might have gone wrong?


  • Mod

    @LastSamurai can you measure the consumption of individual parts? E.g. The Molgan hardware, the arduino and the radio?


  • Hardware Contributor

    @Yveaux Ok I will try to do that. I did try other (new) batteries though and got the same values (about 2V strangely). Then it started to continuously trigger. I described the problem here.
    It's so frustrating, but something seems to be wrong with my whole network I guess....


  • Mod

    @LastSamurai how did you measure 2V? Measured with a DMM 2XAAA fresh alkaline batteries should be more in the 3V range. This makes a big difference, as at around 2V the Pir starts to behave weird, as you already experienced.


  • Hardware Contributor

    @Yveaux I used the vcc library to let the atmega328 measure the voltage and send it as a sensor value to my controller. I guess I will have to investigate that too. Measuring the batteries outside the case with a multimeter I got 1.5V for each one (without any load though).


  • Hardware Contributor

    PS I just measured with the multimeter and the measurements are strange. The board voltage is at about 2.9V (so more like expected) and reaches the atmega as well as the NRF. Overall voltage is at about 4.8V.
    The trigger pad seems to be constantly high though (~2.7V) and the node doesn't seem to show up at the gateway anymore. I guess some serial debugging is needed now. Perhaps some component has died... falsy NRF modules would perhaps explain the errors with my nodes :(

    PPS now the sensor is sending again (strange). The trigger pad is still constantly high though. I guess I will have to desolder the pcb again to have a look at the PIR pcb. Perhaps somethings wrong there...


  • Hardware Contributor

    So I took some measurements and and the molgan pcb on its own works just fine. The mysensors pcb with a stable 3.3V power source worked too. When I wanted to measure the power consumption I realized that a fuse in my multimeter was defect... so I am still waiting for a replacement. Will post an update once its here.


  • Hardware Contributor

    Sorry for the spam here but I have the fuse now and have just been measuring the pcbs.

    • Molgan PIR pcb: 17mA triggered, 7mA otherwise
    • mysensors PCB: 18mA sending, 6uA sleeping

    The second one looks fine to me but the molgan pcb draws way to much power for battery usage, right?! @Yveaux did you measure the power consumption of yours? I just realized that I did not change the resistor that controls the trigger time. I thought 30s are fine but that makes it draw more power too...

    I will also start to test with the second molgan I bought. Really want this to work ;)


  • Mod

    @LastSamurai said in 💬 Ikea Molgan Hack:

    Sorry for the spam here but I have the fuse now and have just been measuring the pcbs.

    No worries, that's what this thread is for, right? ;-)

    The second one looks fine to me but the molgan pcb draws way to much power for battery usage, right?! @Yveaux did you measure the power consumption of yours?

    I did measure it (when I found out the power usage was less with the regulator, than without) but I can't seem to find the results anymore...
    @dynamite mentioned in this thread "The powerconsumption of the PIR when not triggered is approx. 60 uA and when triggered 160 uA.".

    I just realized that I did not change the resistor that controls the trigger time. I thought 30s are fine but that makes it draw more power too...

    Only marginally I guess, unless it triggers all the time.

    I will also start to test with the second molgan I bought. Really want this to work ;)

    Please do so, at least for comparison.


  • Hardware Contributor

    I measured with the new molgan and got nearly the same results. Perhaps my cheap multimeter isn't accurate enough though.
    I moved the mysensor pcb to the new molgan pcb and tried this out. Strange result: at first it only send the initial messages but no triggers. After some minutes the opposite happened: it started to randomly trigger (or at least send them). Then after some more time the random triggers stopped and now its working as intended.
    Perhaps it just the setup time of the PIR or the warmer air coming from a heater nearby... I will keep an eye on it the next days.


  • Hardware Contributor

    Ok I did some more testing and the error seems to be pretty random. Sometimes the PIR works as intended for some time, sometimes it just keeps triggering constantly. I am pretty sure sleeping/waking up or sending the message is somehow influencing the PIR (don't know what else it could be).
    Does anyone have an idea how to fix this (some wait() code or some cap somewhere perhaps)?


  • Hardware Contributor

    i've not looked at the molgan..but for fixing this:

    • if capa to place, that would be directly to the PIR sensor VCC pin (100uf), ideally close to it.
    • or by software : ignoring false triggers, or disable the irq when it's not needed, or slow down a little bit clock during these false trigger.


  • Agreed on the capacitor on the vcc, I had some random triggers on a pir sensor and they were gone when I added a cap to the 5v pin



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