[kgsws] just finished his Game Boy upgrade that allows him to load games from an SD card. Loading a game off an SD card has been done before, but [kgsws] decided to not to use a cartridge-based device. In the end, he threw out all the stops and finished his project by having the Game Boy access an SD card directly.
[kgsws] his project trying to figure out how to put some GPIO pins on a game cartridge, but figured that this would take too much hardware. After looking at the specs of the link port, he realized that it was the wrong polarity. Not to be deterred, [kgsws] realized that there was something like a general-purpose I/O on the Game Boy – the joypad input.
After figuring out the logic of accessing the SD card through the joypad, [kgsws] set to work building a FAT32 parser and a simple BIOS on an EEPROM. The entire system runs off an ATmega32, and he was kind enough to include the schematics and all the code. The end result is really neat – it can load and save 512kB Game Boy ROMs and save data, read .txt files. As an added bonus [kgsws] put in a custom boot logo to replace the top-scrolling Nintendo logo.
While the joypad buttons don’t work when the SD card is being accessed, and the battery draw is larger than the already power-hungry DMG-001, we’re amazed by [kgsws]’s hardware hackery. Check out the video of [kgsws]’s hack below.