Here a straight-forward guide for tapping into the buttons on most gaming controllers. Why do something like this? Well thereís always the goal of conquering Mario through machine learning. But we hope this will further motivate hackers to donate their time and expertise developing specialized controllers for the disabled.
In this example a generic NES knock-off controller gets a breakout header for all of the controls. Upon close inspection of the PCB inside itís clear that the buttons simply short out a trace to ground. By soldering a jumper between the active trace for each button and a female header the controller can still be used as normal, or can have button presses injected by a microcontroller.
The Arduino seen above simulates button presses by driving a pin low. From here you can develop larger buttons, foot pedals, or maybe even some software commands based on head movement or another adaptive technology.

http://hackaday.com/2013/07/13/no-no...ng-controller/