IR air conditioner timer

installed (Custom)

[Tom] has an office job in China. His office is cooled by a small single room air conditioner. In an effort to make his office a little more comfortable, he built this IR timer unit. It cools his office down before he gets there so he doesn’t have to wait for it in the morning. He started by decoding the IR signal from the remote for the unit. He then built this ATiny13 based remote. He notes that the internal clock of this thing isn’t that accurate. power cycling it every day seems to help. It is also pretty cool that he built the unit to not only send the cooling code, but he can switch it to the heating code for the winter.

[thanks Mario]


  1. monkeyslayer56 says:

    very interesting now i wonder what else i can apply that too….

  2. gomer pyle says:

    Wouldn’t it have been easier to just hack the AC unit controller or just wire in a simple timer? Interesting approach but could be accomplished much easier IMHO.
    I can see many applications that could benefit from Tom’s work on this hack. Very in-depth, nice work!

  3. jeremy says:

    @gomer pyle,

    I very much doubt his workplace would allow him to dismantle his AC because he couldn’t wait the 5 minutes for his room to cool down (no disrespect, this is an awesome hack)

  4. Josh says:

    Great idea. If he could find a way to keep the clock accurate it would be even better, maybe a real time clock chip or something?

  5. Sean says:

    The attiny MCUs I’ve used can use an external crystal for higher precision timing. I seem to remember them being orders of magnitude more accurate than the internal timer. The extra components could probably be rigged to fit on the existing board too (just a crystal and two 7-12 pF loading capacitors).

    Alternatively, there is usually an option in AVR Studio to calibrate the internal timer of the MCU to improve accuracy somewhat. I’ve never used it though.

  6. @Sean:

    Unfortunately, the ATtiny13 does not support using an external crystal. An externally generated clock source is supported, but this would require more than just an external crystal. I suppose using a cheap RTC might be the easiest way to get an accurate time source.

  7. deoryp says:

    this is a repost.

  8. hulaghu says:

    Take a hint from old school analog clocks and convert it to use an AC wall wart and pull a pulse from the AC to keep time.

    No more batteries and less drift.

  9. rasz says:

    ya, RTC ripped out of old 286-486 motherboard, or even digital wrist watch from trift store would help with keeping correct time.

  10. Hackius says:

    Why use such a limited uC if he needed more precission? Price?

  11. vonskippy says:
  12. jproach says:

    dealextreme sells “universal” AC remotes for ~$7 which include a clock/timer feature. Still a good project though.

    @vonskippy: even if he had access to the AC power plug of the air conditioner, that may not work. Some units are remote control only, they don’t have front dials and knobs.

  13. strider_mt2k says:

    Yes please, let’s all join the chorus of “you can buy these” on the HACKING WEB SITE.


  14. saimhe says:

    An additional point is that this AC unit is “small”, therefore most likely cheap and dumb. As much as I’ve seen larger ones, they had own timers for this kind of job.

  15. Greg says:

    Great work and a thorough how-to. For those interested in a similar hack involving an air conditioner using NEC protocol, check out:

  16. thammuz says:

    Wow, I was thinking of doing the same thing with my room’s window AC. I only lacked the probes for my newly acquired o-scope.

  17. Nintendo Guy says:

    Pretty cool, seems cheap enough.

  18. Great info. I sent some of my friends to this blog and they thought it was great as well!

  19. kevin tyler says:

    Hi guys

    i want to teach a device the on off code for my air con, so i can mount a light switch sized box on the wall near the air con unit, press on and then an hour later the unit sends the off message, to save electricity when i rent my house out.

    also i do not want to leave the original remote in the house for kids and such to mess with/ break/ or lose.

    any ideas please


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