The Game Boy is connected to the Flipper Zero's GPIO pins via a GBC style Game Link Cable. The Flipper GB Link module is an easy way to connect a Game Boy via a Game Link Cable to the Flipper Zero.
Details on making your own interface adapter can be found here https://github.com/kbembedded/Flipper-Zero-Game-Boy-Pokemon-Trading
Connect a Game Boy to the Flipper through the link cable interface, open the Flipper GB Printer app on the Flipper Zero, configure save files, and the PNG palette the file will be saved with. Press OK on the Receive! command to put the Flipper Zero in receive mode. As files are printed from the Game Boy to the Flipper, the screen will display a count of number of files received, the number of files saved as a PNG (or errors in saving them).
Add Header?: If yes, saves an additional file named GCIM_XXXX-hdr.bin that can be directly imported to https://herrzatacke.github.io/gb-printer-web/#/import.
Palette: Select one of 18 palettes to render the PNGs in. The default, B&W, is grayscale; and all other palettes are all approximations of 2-bit palettes used on real Game Boy devices or emulators.
Select Pinout: Configure the pin interface on the Flipper Zero. This defaults to Original and is likely what you want to use in most cases. Most of the adapters that exist as well as instructions on making custom cables, use this pinout. The MLVK2.5 pinout is used for MALVEKE boards that are hardware revision 2.5 or lower. The 2.5.1 version of the MALVEKE uses the Original pinout.
All files are saved to the Flipper's microSD card, in the apps_dir/flipper_gb_printer/ directory. They are organized in to subfolders dated YYYY-MM-DD/ of the date the photos were printed to the Flipper Zero, and numbered in the order they were printed on each date.
TODO
There is no reason this shouldn't work with every Game Boy game that prints to the Game Boy Printer. However, this project was aimed at the Game Boy Camera and most of the testing has been done there. There are a handful of other games that have been tested and reported to have worked. If there are any games that have issues, please open up an Issue and provide some detail.
This is still in development and does not yet have a lot of features I want to implement. Near term is to support more transfer modes; Photo!'s fast clock and Transfer modes, and Transfer from the Game Boy Camera. A little further out is supporting managing/manipulating frames and Game Boy Camera photos of images printed to the Flipper. And long-term be able to print from the Flipper Zero to a Game Boy Printer. And somewhere in between those, support remote controls for Photo! via IR and link cable. There is also some fantastic animation in the works.