[Al Skierkiewicz]

Japper,
There is an equivalent input schematic on the IFI website. The OI is specifically designed for the joysticks to have one side tied to the +5 volt supply and a series resistance. In conjunction with the internal resistance, the joystick forms a voltage divider. When the port is pulled to near ground, the OI assumes that the joystick has been disconnected and disables the PWM being addressed by that port. Connecting a 50K resistor is perfectly acceptable to simulate a joystick at the rest position. Likewise a 100K resistor should simulate one extreme on the joystick. We use an SP11T switch with 9.1K resistors across each position, connected to one of the ports to give us 11 operator selected auto modes.