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Steering wheel controls: resistance and rotary encoders

alex722607

New Member
Hello, all
This thread is the spawn of a couple questions asked by myself in another thread and I wanted to make this its own topic.
To start off, I am new to this forum and the reason for that is that I am going deeper into electronics than I ever thought I would with my car.

Background on the car: Car is a Pontiac G8, the American version of an Australian produced car.
Background on me: I've always tinkered with electronics but never went too deep, I've done some instrument cluster programming, with eeproms, reading code, researching code and some copying and pasting to experiment with different results. I have also messed around with an Arduino kit but didn't really go to far. Soldering I have done alot of, whether replacing parts on an instrument cluster or other things along those lines. I can put together a circuit board and I have an understanding of what some of the things on a board do. I am also very stubborn and don't give up easy til I have explored every possible solution so whatever I don't know I research. When it goes way above my head or becomes no solution only then I give in.


The project:

The steering wheel was always one of my pet peeves as the feel of it never fit the car. Retrofitted a new wheel but in short newer wheel doesnt match the factory radio in terms of controls, and aftermarket radios look weird in this car so that's out.
Well if I can't change the radio, and I like the new wheel too much to go back to the old one, then I must modify the controls. The original controls had a couple buttons that talked with the radio via two wires by using different resistance values. Then GM got cute and had the volume work off of a rotary encoder (using more wires) similar to the type used in a computer mouse. New style wheel also uses two wires for the resistance but does away with the rotary encoders and instead uses resistance values like the rest of the controls and it all talks with two wires.

Hopefully I haven't lost anyone yet....

So, I can't modify the boards on the new wheel to have the correct resistance because of the way the board is designed, i.e. I change one resistor and affect everything else. So I have to make a converter box to convert the signals from the new wheel to the old radio that is still looking for the old values.

Digging around this forum I found a couple threads and was able to get an idea what it would take to convert one resistance value into another, and that would require turning it into a voltage.

Replicating the encoder signal is the hard part.

Here are the original controls from the original wheel for the radio and their respective resistance values:

Mute - 100 ohms
Talk (pick up phone) - 250 Ohms
Source - 650 ohms
Source up and down - rotary encoder
Volume up and down - rotary encoder

New wheel has these controls:

Mute - 1500 ohms
Talk - 806 ohms
Source - 604 ohms
Source down - 499 Ohms
Source Up - 402 Ohms
Volume down - 301 ohms
Volume up - 1210 ohms

Attached are the two schematics from the two wheels:
The first: steering wheel secondary configurable is the stock wheel
The second: Steering wheel controls 2 is from the wheel I installed

I am making the second output signals to mimic the first
 

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