Checking if the air conditioning is on

  • Hero Member


    I am new to this, and all my hardware is still on transit so this is a theoretical question.

    I want to be able to know what air con units are on, as the children tend to leave them on when they go out of the room. I could think of two ways of doing this:

    1. monitor the LED on the front panel
    2. using hall effect sensor.

    option 1 will probably work but could be a bit ugly. option 2 would probably be the best if I had even the remotest idea about hall effect sensors and how they are used.
    I see that the hall effect sensor from the mysensor store has a hole in it. does the wire has to go through the hole? I can see that the sensor is actually the 3 legged thingie but i am not sure how everything works together.
    Can anyone that knows more about these sensors give some advice if the sensor will actually detect a change in the magnetic flux when the aircon is working?


  • Do you have an air conditioning duct? What about using a temperature sensor?

  • Hero Member

    @Moshe-Livne Are you referring to this sensor: The hole is a mounting hole. You may be able to use a current sensor (see, but as the compressor cycles on and off, the current will vary, so you'll need to do some measurements to determine what the difference is with the air-con on and the compressor off, versus the air-con completely off. Measuring from the LED is not a bad idea, but rather than measuring the light, you can potentially measure the voltage on the LED's wires.


  • Hero Member

    @kunall this is a wall mounted unit, not a ducted aircon. using temperature sensor present some obvious problems, like what should I compare the temperature to.
    @Sparkman , yes this is the one i was referring to. OK, so its a mounting hole.... good!
    I was aiming to detect the current in the internal unit, not the compressor (this is a multi unit system). the idea to hook onto the LED crossed my mind but these are new units, under warranty so I want something that is not invasive, if possible.
    do you think the blower motor will produce enough magnetic field to be detected from the outside of the unit? I am not worried about the on/off cycle for two reasons. one is that these are inverter aircon so they practically run all the time and the other is that eventually the unit will kick in and I will get the alert.

    Thanks for the prompt answers!

  • Hero Member

    @Moshe-Livne , just to give another possibilities: I have a scene in my Vera controller that run on every 30min, and check the status of a motion sensor. If there was no motion over on the last 30min, it turns lights and AC off, doesn't matter which state they currently are.
    Just another way of doing it.

  • Hero Member

    thank @rvendrame , I have considered that as well but I can think of ways it could go wrong, and it requires me to have ir emitter in every room. but it is a possibility. I would prefer to be notified and turn off the AC myself (if i have IR emitter) (or send the kids upstairs to turn it off :-))

  • Hero Member

    @rvendrame , out of curiousity, how do you turn off the AC? is it a mysensor device?

  • Hero Member

    @Moshe-Livne , I use infrared, I have a USB-UIRT connected to Vera (so no my sensor on that). I wasn't able (yet) to reproduce the long IR stream from AC using Arduino, so I can control the AC only at the living room where Vera controller is.
    The motion sensor is a Arduino/mysensor device.

  • You could use a capacitor and an optocoupler. See . Should be much cheaper.

  • Hero Member

    @Moshe-Livne said:

    @Sparkman do you think the blower motor will produce enough magnetic field to be detected from the outside of the unit? I am not worried about the on/off cycle for two reasons. one is that these are inverter aircon so they practically run all the time and the other is that eventually the unit will kick in and I will get the alert.

    Hi Moshe,

    Hard to know for sure as it depends on how far the blower motor is from where you mount it. I would get one to try and see. Are these units hard wired, or do they plug in to a standard wall outlet? If the latter, you could put something in between the plug and the outlet to measure the current draw.


  • Hero Member

    Hardwired, and they did their very best to prevent you from accessing the wires. I guess I'll have to wait patiently for the components to arrive.... Patience comes to those who wait, right?
    How sensitive are those modules?

  • Hero Member

    @Jan-Gatzke, this require to route the current through the optocoupler, right? I can't easily do that...

  • No, it does not. You can connect it parallely to the fan.

  • Hero Member

    @maltimus , this looks just right. I don't know enough to understand what is the difference between this and the modules on aliexpress. this one looks more refined, for sure but other than that I have no idea.... it does seems to be very sensitive if it can detect the difference in the magnetic field being closer to one conductor , so its promising!

  • @Moshe-Livne It should be know what I have not worked with hall-effect sensors so anything I include to this post is purely my understanding from school/research. As current travels through a wire it creates a magnetic field around it. I believe these are so sensitive because both the current in and current out of the AC are so close together and there magnetic fields are cancelling each other out. If you are able to isolate one of the power cables it should be a lot more accurate.

    Can you provide a link to the system?

  • Hero Member

    @maltimus if by "the system" you mean the air conditioning unit, it is a relatively standard split unit with compressor outside and fan on the inside. getting to the wires is not trivial and will probably void the warranty, so non-intrusive is the way to go.
    what i will do is wait for my stuff to arrive, and build a sensor and just see what it reads. as there is a large motor rotating on the inside i hope it will leak magnetic field. if not, there is always the LED....

  • Just a thought, those internal portions of the split system airconditioners have diffuser vents that open when the unit turns on and close when its turned off. You could fit a magnet to one of the vent blades, and use a magnetic reed switch to tell the system whether the vents are open or closed. That could be translated by MySensors as the unit running or turned off.

    The plus side of that is that a reed switch costs pennies, and can be bought in a number of colours, so you should be able to colour match the aircon unit pretty closely. You can attach them with strong double sided tape if you cant screw into the unit as well (Use Automotive grade double sided tape, that they use for fixing badges on cars, works a treat), so it shouldn't void any warranties.

  • Hero Member

    @Chester That is actually a great idea.... From what I read elsewhere it seems that the cheap hall sensors are not that sensitive so your idea should be the bestest... Thanks!!!

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