Nintendo’s eReader, an optical card reader developed by Olympus using their “Dot Code” technology, is a small add-on for GBA users. Players can scan (hideously overpriced) trading cards into their GBA to play games and unlock extras. Each card has a dot code printed on it that stores a couple of kilobytes of code – that code can be an emulation of an early Game and Watch title, or it can even be a smart new umbrella for your Animal Crossing character.
Cards are the same shape and size as standard playing cards (though without the naked ladies on the back) and are available in packs of five or so based on popular Nintendo franchises: Animal Crossing and Pokémon unlock or upload new aspects to the games, or you can even upload the classic Donkey Kong 3 to your GameBoy Advance.
The dot codes use Reed Solomon error correction and now that the scheme has been worked out, homebrew coders can finally write their own games for easy distribution to GBA owners. Tim Schuerewegen cracked the code and is hosting an original game – BombSweeper. Coders interested in writing for the GBA can even use GNU GCC to compile code – plus the API for the GameBoy Advance is very well documented.
The eReader has been modestly successful, but never set the world alight. In fact, support for it seems to have been quietly dropped. Try plugging one into your GBA SP and you’ll see what I mean – it no longer fits. The link port on a SP is now on the opposite side of the console, so the eReader can’t slide fully into the cartridge slot.