https://www.google.com/patents/US8241126
Video game controller having user swappable control components
Original Assignee: Valve Corporation
Abstract:
A game controller is provided. One or more main control input interfaces on the game controller consist of generalized sockets. A variety of modular input interfaces can be plugged into these sockets. Hardware specific to the input type of the modular input is contained within the modular input itself, and plugged in via an interface. This allows for dual analog sticks, a combination of analog and trackball, or further any combination of touchpad, directional pad, or additional components.