03-28-2021, 10:19 PM
Yeah, like I said on my Honda, I had the resistor values from the Service Manual.
Basically, I'd get to the steering wheel controls, and measure the DC voltage to ground from both the analog pins. Then I would press the mode button, and record the voltage that changed. The I would go to the other analog wire, press all the buttons, then record the voltage for each button press.
I would then disconnect the plug to the buttons. At that point you'll have to put the ground lead of your voltmeter on the pin that is ground for the steering wheel controls, as when you unplug it, you are also unplugging ground.
With the meter set to Ohms, record the Ohms reading for both wires with no buttons pressed, for the mode button press, and then the other wire's multitude of button presses.
With those voltages and ohm readings, we can determine the resistor values in the wheel, the supply voltage, and probably even the resistors in the radio between the supply and the plug going out to the wheel controls.
I know in my Honda, after taking those measurements, I confirmed the values in the steering wheel, and found that the supply was actually 5V. I also calculated the resistor that was inside the radio. It was a little more important in that case as I used digital outputs of the Arduino to trigger opto-isolators to simulate button presses on a twin to the resistor ladder that was in the wheel. That way the Arduino could do button presses as well, and the factory stereo could read them.
Basically, I'd get to the steering wheel controls, and measure the DC voltage to ground from both the analog pins. Then I would press the mode button, and record the voltage that changed. The I would go to the other analog wire, press all the buttons, then record the voltage for each button press.
I would then disconnect the plug to the buttons. At that point you'll have to put the ground lead of your voltmeter on the pin that is ground for the steering wheel controls, as when you unplug it, you are also unplugging ground.
With the meter set to Ohms, record the Ohms reading for both wires with no buttons pressed, for the mode button press, and then the other wire's multitude of button presses.
With those voltages and ohm readings, we can determine the resistor values in the wheel, the supply voltage, and probably even the resistors in the radio between the supply and the plug going out to the wheel controls.
I know in my Honda, after taking those measurements, I confirmed the values in the steering wheel, and found that the supply was actually 5V. I also calculated the resistor that was inside the radio. It was a little more important in that case as I used digital outputs of the Arduino to trigger opto-isolators to simulate button presses on a twin to the resistor ladder that was in the wheel. That way the Arduino could do button presses as well, and the factory stereo could read them.