SOLVED: Magnetic sensors failing on my side-by-side freezer

Hi All

I’ve gotten these very simple 433 MHz sensors with two states, one for open, one for closed.
They work all over the place, except for my side-by-side fridge.
I suspect the two sensors / magnets are too close to each other (they are placed on each door, ~20 cm apart), as seen here:

So I am considering an alternative. Maybe something like a mechanical switch

connected to a Wemos D1 mini, anybody else that has a good idea?
I guess I should place a resistor like 10 kOhm’s on it or could I just use GPIO0 and GPIO2?
My idea was that when the arm was open, it will be ‘on’, so that it will be off most of the time, when the fridge doors are closed, and thus put pressure on the arm.


Are they far from your gateway?

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That was my first thought as well, so moved the sonoff bridge almost next to it (1,5m), so that’s at least not the issue any longer.
I have other 433 MHz sensors, which were close to the gateway previously, and a now equally long from the gateway now, as the fridge sensors were before, and they don’t have a problem in transmitting to it.

Just for my curiosity, what’s the final use case of putting door sensor of your bridge?

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To warn the family if it’s not closed, the kids sometimes just slams it, and if they have moved items around especially in the freezer, they might move so the door doesn’t close, and they don’t notice that.

I was asking myself also if a bluetooth sensor with an esp32 as a gateway could be a solution.
With that you are also covering the potential fridge failures.
If you are interested I can do some tests by putting a mijia inside a fridge and see if we get the signal.

Regarding your issue, if you put only one sensor (remove fixed and mobile part) do you get the same problem?

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presumably the doors are metal? And the door seals are magnetic?

Neither of these will help the working of a reed switch and magnet pair.

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Tests are OK with an esp32 located at 2 meters from the fridge:

hmm, my fridge seems a bit hot

That is true, the doors are metal, and I’m guessing the seals are magnetic, they will of course affect it, didn’t think of that, thankyou!

as @1technophile suggests, if you can, try with just one pair. And try swapping the reed and magnet. And try something like putting them at the top of the fridge…

I’ve got a xiaomi door/window sensor on my metal garage roller door - the magnet is on the moving part, the sensor glued to the track (also metal) - this works for me…

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That sounds very cool, how long does it run on the battery? I’ve ordered the mechanical switches for now, and I’ll be placing a D1 mini or as you suggest an ESP32 for later expansion with the BT mijia sensor

I did try that, and thought it helped at first, but not really.
They are placed on top of it.

I don’t have did the test on a whole battery cycle but I think we can expect 1 year on normal conditions (I don’t know how it will behave into a fridge)

Thanks to your question I have now one mijia sitting definetely in my fridge :slight_smile:

:laughing: Well, for one year, that sounds like it’s a good solution.

Florian, Digoo R8H also works fine inside the fridge and signal passes through two additional walls; battery life is a little lower compared to another unit I have in the bathroom (didn’t put a DHT22/BME on ESP/Arduino due to moisture so risk of electrical shock).

But R8H doesn’t work with OMG yet. I tried with verbose debugging activated, but the gateway didn’t react to it, which I think is due to not being implemented by PiLight.

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Seems coherent as 433mhz has a better penetration compared to 2.4ghz used by BLE.

I have one R8H in the boat to my house, I will see if I can integrate it, once received.

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If you poke me in one month I will be able to give you the battery discharge rate into my fridge. It will enable some approximation on battery duration.

Thanks for giving the idea.

For the story a few days after I added the mi jia to my fridge I saw that the temperature went high.
It was due to high temperature in France and a too old fridge I think.

The sensor enabled me to take appropriate actions for the food inside it!!

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Hey, that IS cool (or maybe not, depending on the fridge :smiley: ).
Great that you had it set up!