This is really amazing, thanks for sharing! How did you know which pins to look at? And do you know what the other pins do? I’m super curious now, and actually have an original gameboy which I now want to open up :-)

I wonder if these same signals can be used to make an adapter to connect an external screen.

You figure out which pins to look at by time consuming painstaking trial and error. :)

Something that I think is even more interesting is that someone made a screen capture device that would go between the cartridge and the console and work only based on what code the game was accessing by reconstructing the entire state of the Game Boy based on what paths were taken in the code

https://there.oughta.be/a/game-boy-capture-cartridge

So cool and really love that people still found even less intrusive ways to capture gameplay:

https://there.oughta.be/a/game-boy-capture-cartridge

https://news.ycombinator.com/item?id=34069305