Air Conditioner Regulation Using A Hobby Servo


For anyone that works in a large office building, odds are you know the pains of dealing with a poorly regulated HVAC system. [Robovergne] and his co-workers recently moved to a new location, and found that the air conditioning control was less than effective, leaving the office as hot as a sauna or as cold as a meat locker.

While they manually triggered the A/C on and off every half hour for a while, that grew tiring, so [Robovergne] decided to take things into his own hands. He had never used an Arduino before, and figured that regulating the air would be a great first project. He mounted a small hobby servo onto the front of the A/C remote, and wired a DS18B21 temperature probe to the Arduino. A small pot is used to adjust the temperature setpoints, which are displayed on the attached LCD screen. Now, when the temperature starts to rise, the Arduino triggers the servo to turn the air conditioning on without human interaction.

[Robovergne] says that while his solution is ugly, it works quite well. It definitely gets the job done, we can’t argue with that!

Continue reading to see a video of his automatic A/C controller in action.


28 thoughts on “Air Conditioner Regulation Using A Hobby Servo

    1. I like that idea, but could he maybe just get a $10 learning remote from target and do that?

      Nice job on the first hack :) I don’t mind the ugly one bit :) Enjoy the AC!

      1. But who would push the button on the replacement learning remote? It wouldn’t automagically act as a thermostat either.

        Or do you mean train the cheap remote, then tear it apart and solder the wires from the Arduino directly to the replacement’s button? Sure, it would probably be cheaper, quieter, and more reliable than a hobby servo and scotch tape, but where’s the fun in that? :-)

  1. >>cool idea.
    next step would be to reverse engineer the IR protocol and use the arduino as the remote(?)

    Actually… that should have been the first step… or even without really decoding the full protocol, just recording the proper command would have sufficed…

    I’m not saying what he does is the wrong way to do it, it works so it’s good for him. Meanwhile, the redneckness level of this hack make its value for publication a little doubtfull…

    1. I think the point of this is a simple solution to a problem. I have done things like this before, then created a more polished based around what knowledge I learn from the first project. Not everyone has the knowledge and skills required to build finished-project or factory looking projects. I do give them credit for trying and helping to inspire others.

      1. I agree. I think simplicity is the main goal, but another goal of sharing is so that an idea can then go through several permutations as others see it and begin to make changes so that it fits their liking. To me, that’s the whole point of hacking. HaD provides a forum where these ideas can be exchanged.

    1. I agree, rube goldburg everything to extremes! Also both the taped on servo and IR decoding serve to protect the control case that the company might not own (rented office perhaps?) bypassing the remote would be the most efficient way to do it but where’s the fun in that?

    1. Window units generally don’t have thermostat contacts. What I did for mine was set it at max-cool, and use a relay in a box to turn the power on and off at the plug. Only really works for a full manual one though.

  2. Awesome hack! Personally, I would have just grabbed a PID controller out of my junque box and wired in a cooling relay. However, I realize that most people don’t have stuff like that on hand.

  3. Another vote in support of redneck engineering. Trust me, when your A/C isn’t working right, coming up with an elegant solution is usually the furthest thing from your mind!

  4. It’s a hack. It’s quick ‘n dirty, and it gets the job done. Is it the most elegant solution? Maybe not, but it’s in place, and it’s working. Two thumbs up! It’s exactly the sort of thing that should be posted to Hackaday.

  5. So, it has a remote, and they are too lazy to even use the remote? I thought this was for a thermostat on the wall that they didn’t want to walk over to every half hour.
    At least it does trigger it when the temperature starts to rise rather than having to keep watch over the temp on your own.

    1. The whole point of this is to avoid the need for user intervention, WITHOUT having to crack open the casing, splice something into wiring, or do anything else that would have the building maintenance people coming up to visit with pitch forks and torches. Remember, this is a workplace. If you suggest anything that involves modifying existing hardware or wiring you’re proving you didn’t read before you posted.

  6. Good starter project.
    As suggested next step , reverse engineer the IR protocol. It is really easy to do since you already have an arduino. Get a IR receiver module, cost about $1 and connect that to an arduino digital in.
    Once you know what the correct bits are then you just need an IR diode and transistor to send the signal and can get rid of a lot of extra stuff you currently have to use.

    The sensor is :

    the diode is:

  7. thermostats R cheep . Nice application of tech, I might have done something similar, if the parts were just on-hand, but then I would have simply replaced the thermostat. I’ll assume for now you are planning to do either that or complaining bitterly to your landlord. Gotta free up that kit for other hacks!

  8. Great hack!! Sounds like you’ve got an air conditioner which is over-sized for the room.

    I would have bought a cheap programmable thermostat at the local home center. Wiring for thermostats are usually easy.

  9. The comment about the AC being oversized is probably the most observant comment out of the bunch so far.

    Sounds like the HVAC contractor was incompetent (which isn’t an uncommon situation). Someone probably did not do a proper heat loss (“Manual J”) calculation and now you have a system that fails to properly remove humidity from the air.

    Turning off a compressor based on temperature is pretty simple. Sizing the compressor to the building envelope and taking into account the volume of air that needs to be “conditioned” is something a lot of contractors are incapable of figuring out. Some states require an engineer to do the numbers for precisely that reason.

    The building owners should bring in QUALIFIED contractors to properly fine tune/optimize the entire system. Just running compressors till it blasts cold air out isn’t going to do $hit !

    1. It just might be oversized, but it all depends on the building – truth be told, I have no idea how the A/C was installed at Robovergne’s office

      Where I’m at, there’s a chiller in the penthouse and everyone feeds off of that. Cold water runs and (overzealous) fans do the rest of the job, keeping the office way too cold. I just wish we had the ability to toggle the fans on and off – any regulation requires calling in a maintenance tech to play with the baffles in the ceiling.

  10. neat! I have been looking for months on how to make an arduino control my a/c.. i think it would be cool to try and figure out the most perfect efficient way to run my a/c.. i come home from work around 7pm .. and i would like it to be 74 degrees when i get home.. how long, depending on the current temperature of the house, would it take to get the house to 74 degrees at 7pm?!
    .. then depending on the electricity usage.. take a constant running toll of how much electrity it is using, plug in my cost of kw/hr.. and i know how much my a/c is costing me at any moment.. and what to expect on my next electric bill!!
    project anyone.. kickstart???

  11. Hi all. I’m the author of this hack.

    I discovering the word “redneckness” today, I like it :o)

    As many stated, there would have be plenty of smarter solution to solve this problem, but :

    – I would probably get fired if I did intrusive hacking of my workplace or do anything that ruin the remote.
    – I didn’t want to spent too much time to get a neat solution, since I was expecting the problem to be solved the right way by the AC tech.
    – the button pushing robot make my colleague smile when they get into my office, which is far more important to me than making something smart ;)


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