I built a FM radio cartridge for the Game Boy. Unlike existing FM tuner accessories, this cartridge is fully controlled by the Game Boy, and can output sound directly into the Game Boy’s speaker using a rarely used feature of the Game Boy’s cartridge bus. I call this cartridge “Orange FM”, and I spent nearly two years developing it. There’s much more information on the Orange FM website.

Orange FM box

Orange FM interface screenshot

This was by far the most complicated project I’ve done to date, largely due to the densely packed circuit board, and strict design requirements needed for good FM performance. It took me seven revisions of the circuit board until I had a design I was happy with! The board is packed with the venerable ATmega328 microcontroller, flash memory, multiple discreet logic chips, and of course a Silicon Labs SI4705 radio chip. This chip is packed with useful features, chiefly the ability to have dual antennas. My design has an internal trace antenna, as well as the ability to use an external antenna, which can even be a pair of attached headphones.

There are two audio circuits. First, a simple op-amp circuit to drive the signal into the Game Boy’s sound hardware through the cartridge bus, and second, a headphone amplifier that can send high quality stereo sound to a pair of headphones attached directly to the cartridge.

Orange FM circuit board

Orange FM is available for sale at insideGadgets, a small Australian company that produces their own range of Game Boy cartridges and modifications. They’ve been able to make OrangeFM globally, and I reguarly hear from people using it in Japan, France, and countries all around the world!

The Verge did a short video featuring Orange FM, which was a neat thing to have happen.