Digital to OI Analog

[marcan]

Has anyone tried interfacing digitally generated signals to the OI? Everyone seems to be using potentiometers like the original joysticks, but using a DAC is obviously possible (see the USB-Chicklet). Does anyone know what the requirements are for the analog inputs of the OI? Given a schematic of the OI input section it should be very easy to design a circuit that works as intended, but I need to know what the inputs rely on to tell what the joystick value is.

My guess is they have a fixed resistor to GND and use the pots (wired to +5 on the joystick) to form a voltage divider, which is then measured using a PIC's A/D converters. In this case, driving a constant-voltage output (buffered using an op-amp if needed) would essentially make the resistor meaningless and allow you to directly control the input proportional to the applied voltage (from an A/D converter, for example). However, many other input systems are possible, including using capacitors to form an R/C circuit and measuring the time it takes to charge/discharge, or using a more complicated arrangement with resistors.

Has anyone taken apart their OI? I'm going to assume it's been the same over the past few years. A schematic or picture from the input section of a 2005 OI would be awesome