Interfacing resistor ladder multi-inputs to resistor ladder multi-output

Hi all,

Starting a project which involves reading buttons in from a car's radio button stalk which uses a resistor ladder to get multiple inputs on a couple of wires. What I need to do is read and convert those same inputs into the equivalent but different value resistor outputs. At first I thought of using multiple transistors with the appropriate resistor for each button but I felt that would be a dirty solution and perhaps problematic with multiple transistors which cannot connect to system ground. Then I thought recently maybe I could use a digital potentiometer however I wouldn't know how to get the value I need or whether or not the value would be close to tolerance of the audio device.

To add more details, both systems are from the same manufacturer of vehicle and model but one is a much newer system. Both have all the wires going to the unit and none of these are ground or power, I dont know what system they use to sense the resistor connections and grounding them does not work. The eventual board needs to be at a resonably small size, ideally using the Arduino Pro Mini/Nano and not too much larger size but this isn't a strict requirement.

If anybody has a good idea on what method would work for this, I'd be all ears

The digital potentiometer is the way to go for the output. However most digipots are limited - the output voltage cannot exceed the control voltage. So you can't use a 5V Arduino to control a 12V digipot.

I'm sure they must exist, even if you have to pass the control signal through a level converter. But I don't have any part numbers close to hand to tell you which one to buy.

Failing that, amplify a "proper" analog output up to 12V. Opamps are good at producing small (current) signals at reasonable voltages like 12V. The proper analog can be made from an Arduino PWM output with some filtering components.

Sounds like a good plan. I don't know if the voltage will creep to 12v as they are interfacing with lower voltage systems but I guess nothing beats a good probing when dealing with the unknown. It's a voltage I'm expecting to see and all I need to do is calibrate the pot to give that output?