Aside from a colour screen and an option to boost the processor’s speed, the Game Boy Colour included an infrared port that was mostly used for sharing data, like high scores or unlockable characters. One tinkerer found a better use for it, turning a gifted GBC into a remote control for his air conditioner.
Curious what else the IR transmitter could be used for, JinGen Lim (their chosen username) discovered a long-forgotten GBC Mission Impossible game that included PDA functionality, including a software-based learning remote that could control TVs and other devices wirelessly, long before wifi or Bluetooth was readily accessible to consumers. Instead of digging up a copy of the game, however, they decided to start from scratch.
But creating custom software for the Game Boy Colour wasn’t as easy or accessible as creating apps for Android or iOS mobile devices is today. The only way to get the GBC to run custom code is by putting it on a cartridge. Special carts that can be loaded up with multiple ROMs are available for the GBC, but are expensive, and official GBC game cartridges can only be programmed once at the factory. Bootleg cartridges aren’t similarly limited, however, and with a $US30 ($46) programming card, they can be easily written over with custom code.
Excited to be able to control my air-conditioner with a GameBoy Color, using my own ROM!
— JinGen Lim (@jg_lim) April 27, 2020
Infrared remotes work by simply flashing a series of light pulses (invisible to human eyes) at another device to send instructions or data, and to determine the patterns used by his air conditioner remote to talk to the appliance, they opened it up, soldered a wire to the IR emitter, and captured the electrical signals through his computer. This allowed him to decode the signals for various functions, like power, and temperature adjustments.
This groundwork meant that they didn’t have to develop a GBC app that could capture and learn instructions, it basically just had to turn the console’s IR emitter on and off. There were a few additional challenges along the way, which they solved by borrowing some unorthodox tricks from Nintendo itself, but eventually, he was left with what might be the most boring Game Boy Colour cartridge ever developed. Hopefully, he’ll continue to develop the app, and maybe even gamify the process of adjusting the temperature in a room. Imagine having to clear a line in Tetris for every degree cooler you wanted it to be.