How to keep a room comfortable before you enter without running a cooling or heating system all the time? That is the problem that was faced here. The solution was to use IR to turn the system on automatically by making a Hacked Air Conditioner Infrared Remote Control.

Via: Elektronika

Thanks Mario.

"Here in China, there is no central air, so my office is heated/cooled by a room air conditioner. Because of this, it’s cold when I arrive at work in the winter, and hot in the summer. So an idea was born to create a small, battery powered, IR emitter that would issue the same "ON" command the AC’s remote control does, but does it an hour or so before I get to work in the morning. Timing will be handled by using the watchdog interrupt. The watchdog will fire every 8 seconds (450 ticks per hour). If we set up a 24 hour counter, then the counter should roll over every 10,800 ticks. If we start our IR emitter at 5:00pm we should initialize the timer counter to 7,650. We want the IR emitter to send the "ON" command to the AC unit at 7:30am (3,375 ticks), then again every 10 minutes (75 ticks) until 8:30am (3,825 ticks)."