I am trying to make a macro controller for the right joystick of my xbox controller but all the other macro controllers i've seen had the joysticks removed and digipots put in their place, but i want to keep the joystick in there but still be able to control it. The joystick works by using 2 potentiometers in the x and y axis to figure out where the joystick has moved to. Im not that good at electronics but i thought a transistor will cause a voltage drop and mess up the signal. Could i just wire the digipot parallel to the potentiometer? Is there any other ways of working around this?
No, you cannot blithely force the output, for if the pot and the digipot were at opposite
ends the power supply would be shorted out.
Fortunately joystick pots are normally physically restrained from travelling full range,
which if is the case lessens this difficulty, but you still have the issue of the output depending
on both the physical pot and digipot "positions", whereas you want to strictly override it.
The circuit that springs to mind is add a 10k or similar in series with the wiper on the
physical pot, then use a DAC and an analog switch to override the voltage further "downstream". Digital pots are rarely needed outside of hifi systems, here a DAC is
a simpler and more capable choice. The analog switch would be turned on to connect
the DAC output, and then the physical pot would be isolated via the 10k resistor (assuming
the DAC and analog switch have low impedance) and no longer have meaningful effect
on the output voltage.
However the details rely on knowing more details of the circuitry currently in the
joystick.