Hacking Sensor Interfaces - MSc Sound Design

Hacking a Game ControllerA typical game controller features two joysticks and lots of buttons (often 16 or more). The “HumanInterface Device” or USB-HID specification defines how software should read it, and so any software thatcan talk HID can read a game controller (and mouse, keyboard, trackpad and so on).To read a game controller in Max/MSP you use the hi object, while in Pd there’s an equivalent hid object.Analogue joysticks are built from two potentiometers mounted at right angles. If you take off the case youwill be able to see where the three pins of each pot are soldered into the circuit board. The simple trickinvolves removing the joystick (the hard bit) and replacing the pots with sensors in voltage divider circuits(or replacement 3-pin pots) as mentioned above.Depending on the design of the circuit board you might find it easier to cut the legs of the pots in thejoystick and then de-solder the remaining stumps with a de-solder pump. Watch that you don’t damagethe rest of the circuitry on the board while de-soldering.The photo below shows a Logitech Cordless Wingman controller with one joystick removed and twopotentiometers added in its place. The one on the right is a multi-turn pot, which has to turn 12 completecycles to change from minimum to maximum resistance.For detailed tutorials on game controller hacking, see Andrew Benson’s tutorial on the Cycling’74 website,or the chapter in Nicolas Collins’ book. (Details on both are below.)Chris Hand 28/1/10 6/10