Replace an inductive joystick with a micro controller?

I recently bought a Pride Mobility Jet 1 power wheelchair on ebay, thinking what a great base it would make for a robot project. It's
controlled by a Dynamic DL50UBR9 controller. As I investigated what it would take to control it with a micro controller, it seemed that mimicking the joystick would be the only real option. I found that the joystick is inductive and that the black and red wires are ground and 5v, and the other four--yellow, brown, blue, and white--control forward, reverse, right, and left motion respectively. 2.5v seems to be neutral, and the voltage is varied from 1v to 4v by the joystick. I thought I could mimic the joystick by applying the correct voltage to these wires, but when I put a variable resistor between 5v (red) and forward (yellow), the controller reset. I couldn't find a manufacturer or part number for the joystick. I'd appreciate any suggestions on what it might take to make the controller think it's listening to a joystick when it's really a micro controller doing the driving.
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mbendio wrote:

What you probably need is a potentiometer, not variable resistor.
Connect one end to +5, the other to ground and then the moving wiper will go to your input.
To restrict the range to 1 to 4v, put fixed resistors in the two end connections - something like GND -- 1k2 fixed --- 5k pot --- 1k2 fixed -- +5v
Note that micros do not usually have a simple variable output voltage - you will probably need to use PWM (Google for that). You will probably need some sort of filtering on that PWM output to avoid confusing the drive controller
HTH Dave
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Here is what I've found out: Note that the yellow and brown wires both control speed--the voltage on the yellow wire ranges from 1v-4v when the joystick is moved from all the way back to all the way forward, and the brown wire also varies from 4v-1v for the same movement of the joystick. Similarly, the voltages are mirrored on the blue and white wires for right and left movement of the joystick. In order to mimic the joystick, mirrored voltages must be applied to the pairs that control speed and direction. For example, keeping in mind that 2.5v is neutral, if 2.5v + 1v is applied to the yellow wire, 2.5v - 1v must be applied to the brown wire. This is a sanity check for the joystick. If mirrored voltages aren't present, the controller thinks the joystick is broken and goes into a fault state.
In addition, the neutral voltage--2.5v--must be present on all wires for three seconds when the controller is turned on as an additional check on the state of the joystick. Permissible control voltages actually vary from a little over 1v to about 4.7v.
It should be possible to create the control voltages using PWM through a low-pass filter.
Hope this helps someone else. Power wheelchairs seem very promising as robot bases. I found one on eBay for $75.
Dave wrote:

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