http://atariage.com/...nsoles-cheaply/ it has been done for a few years now. I have SNES mod done but I skipped the 90° rotate feature. Few games are designed for this and it's hard to make my 32" TV stand on sideway while using separate controller.
Early controllers like Atari 2600 and SMS won't need anything special but they don't have enough buttons unless you go with the expensive Neo Geo controller (15 pins connector is big though and would be hard to add that without making Lynx ugly).
SNES and PSOne controllers are common and easily obtained but they use chip to encode multiple buttons over few wires so you would need decoder to handle the conversion. ATMega 328 is cheap (about $2 from legit sources) if you can program it yourself. I have looked into and PS2 controllers don't work well because it doesn't like 5v from Lynx and I am too lazy to add in bunch of level shifter and 3.3v power converter just to make PS2 controller work. XBox (original) uses propriety USB and both original and S model don't fit well in my hand so I never looked further in this. Gamecube is a possibility though, I have Wavebird. I could connect wirelessly and leave my Lynx next to my TV.
Mine has all the functions, except for the three buttons on the left of the Lynx screen, so: ON, OFF, BACLIGHT which are unnecessary on an external controller.
While it has all the other functions, so if you press together OPTION1 and II on the controller, you will have RESTART. Also if you press II and OPTION2 together you will have the FLIP function, so the 90° rotate feature you were talking about. Even if this feature is unnecessary playing on a monitor....
The aesthetic result is good, in my opinion. Also for the connector on the Lynx...
Edited by ATLynxer, Fri Apr 7, 2017 12:53 AM.