Hacking steering wheel controls to radio

Discussion in 'The Projects Forum' started by therossinator, Mar 17, 2014.

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  1. therossinator

    Thread Starter New Member

    Mar 17, 2014
    I never did well in my EE classes, I got Ds in them both semesters. Now I am doing projects of my own and love working on circuits outside of the classroom. I have designed and assembled my own solar system atop an Airstream trailer complete with MPPT, battery bank and sine wave inverter. I hard wired all of my electronic components to the 12v battery bank and use 12v to 5v cigarette lighter USB adapters for the smaller stuff and a 12v to 19v for my laptop charger and my mini projector.
    I've really enjoyed it all and am always eager to learn more, but enough with introductions.

    On to my current project:
    I have a car radio that I want to add steering wheel controls to. The steering wheel already has the buttons on it but due to the limitations of the wiring harness and steering column limitations I can only use 2 wires to get to the 4 steering wheel buttons. The buttons on the wheel itself I want to be used for volume up, volume down, track up, and track down. I know some aftermarket car stereo wired remotes use resistor networks and I wanted to use the same theory: have one wire going in and each button has a different resistor on it and the voltage drop on the other end of the wire will determine which button I pressed.
    Based upon which button I pressed I want to send voltage to the gate of one of four transistors. Each of these transistors will close a circuit in the faceplate of the radio, acting just like I pressed a button on the faceplate itself.
    Can this be done?

    The buttons in the faceplate are all connected to an IC (PCF8574T) and the detachable faceplate connects to the radio via 6 contacts. Is there a way I could use these contacts to utilize the functions I mentioned earlier(vol up, etc.)? From looking at the IC data sheet it looks to be digital, it seems to utilize a clock which I guess if for detecting long button presses.

    Any guidance here would be very much appreciated.
    -Jeffrey Rossman
  2. MrChips


    Oct 2, 2009
    The owners of All About Circuits have elected not to allow discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Here is a site that may provide you with some assistance: Electro Tech Online

    Good luck.
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