Steering wheel controls as input to Arduino?

I am a complete novice when it comes to the Arduino but I do have an electronics background. On to my project... I have a Pontiac Grand Prix with steering wheel mounted radio controls and this past Christmas I was given an iPod touch. Now I want to mate the two together. The steering wheel controls are a resistance based input circuit that feeds into the back of the radio. Apologies for the bad image, I can upload a better one this evening.

I'm not exactly sure what would be sent to the radio but I'm assuming it detects a voltage level based on which circuit is completed by the series resistors.

Does the Arduino have a built in method to detect something like this or would I need a go between to interpret the voltage level and then feed that as serial data to the Arduino? I found some similar requests around but not the complete info I was looking for.

I basically want to pull out just the next and previous track button pushes which I know I'll need to then send out of the Arduino as serial communication to the iPod. For now I just want to see if I can get the input to work before wasting my time on the output.

Thank you for any help!

Here is the image:


You can use this: And use the T1 of the car wiring to the arduino analog pin, but you will need to change the voltage to the buttons, from 12v to 5 volt, or maybe add a resistor to between T1 and the arduino analog pin, so you dont get a voltage thats to high for the arduino to handle.

Best Regards

or maybe add a resistor to between T1 and the arduino analog pin, so you dont get a voltage thats to high for the arduino to handle.

Shouldn't that be "a resistor between T1 and ground, to act as a voltage divider to bring the voltage down to a 5V level for the Arduino"?

You could also supply the voltage from that battery (if it is the 12V car battery, for instance) to the AREF pin on the Arduino, I think - see here for an explanation:

It might be easier to supply the 5V to the circuit (what is B1, btw - is it the car's battery, or is it a separate battery in the controller on the steering wheel?), as you noted...

Not sure that AREF can exceed VCC without damaging the chip

Here is the actual circuit:

I guess my next steps should be figuring out what the radio supply voltage is (I assume ~12 volts) and then using a meter at the other end of the radio input to see what the max voltage going into the unit is when each button is pressed. Actually, I guess I just need to know the voltage when the volume up button is pressed since every other button will be a lesser voltage? It looks like the input is tied to chassis ground through a resistor? I guess depending on what the resistor is that's tied to ground internal to the radio I may see smaller voltages on the dark blue (D-BU) wire feeding the radio?

This is going to be a fun project...

Integrate steering wheel controls with Arduino Get Arduino to talk serial to iPod when steering wheel controls are pressed Power arduino and ipod charging from 12 volt source