I've been looking for a equivalent of Famicom Hori Game Repater but for Gameboy. I couldn't find such device so I am thinking about making it myself. Is it possible to send input to GB by EXT port? Or i should send signals directly on a board? And what kind of processor should I use to make it easy and cheap?
maybe you could make something arduino or pi based.
I guess so but I am quite new in the topic and would like to know some more, how to connect it to Gameboy and make it work.
You need to look over the GamBoy technical information. Luckily, the schematics are available online, and far easier to read than say, the Famicom's schematics.
http://fms.komkon.org/GameBoy/Tech/GameBoy.gif
and here's the EXT port pinout.
http://www.retroisle.com/others/nintendogameboy/Technical/Hardware/GBpinouts.php
Examine the EXT port pathways and go from there.
But don't expect help here. We aren't engineers. Find an electrical engineering forum and ask.
I fought that maybe someone on this forum tweaked in GB and/or microcontrollers so can share an idea how to realise this. Anyway thanks for the schematics.
If anyone did, it's probably 80sFREAK. That dude is an electrical genius.