Sim-Racing-Shields VS 32-FUNCTION-BUTTON-BOX

Both the library and the shields are open source (LGPL and GPLv3, respectively). You can download the library here, and download the shield files here.

There's more info about the project on my website, and you can find all of the files to make your own on GitHub.

I'm using an Arduino Micro myself to control my G25 shifter and pedals, a DIY loadcell handbrake and DIY button box. My code is originally based on the one amstudio shared for their 32 function button box, as that was initially its only task. I then built my handbrake and added some code to handle the HX711 loadcell amplifier.

I've not used a port expander personally but they seem pretty simple wiring wise, so they should be fine. You don't have to go through SimHub with a button box, the classic AMStudio sketch https://github.com/AM-STUDIO/32-FUNCTION-BUTTON-BOX works fine too (on a leonardo or pro micro).

You can find examples all over the Internet. AM-Studio for example: https://github.com/AM-STUDIO/32-FUNCTION-BUTTON-BOX If you want to build your own Design you will need to learn a bit about electronics and arduino programming.

ProMicro Leonardo using the AMSTUDIO 20.8.17 code https://github.com/AM-STUDIO/32-FUNCTION-BUTTON-BOX/blob/master/ARDUINO_BUTTON_BOXV2.ino

I'm using an Arduino Leonardo with a heavily modified version of this sketch. I guess I could switch over to MMJoy, but it seems like there's a lot going on there. It seems to replace the bootloader for some reason? I'll keep it in mind, but honestly it seems more confusing than just writing my own calibration routines, haha.