How eight buttons work with four wires?

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  1. How eight buttons work with four wires? 
    #1
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    Hi to all,

    I have been trying to understand how my E39 knows which button is pressed on the steering wheel?

    There are 8 buttons in total on my wheel yet only 4 wires coming from the wheel to the harness. Does the system recognise which button is pressed by a differing resistance or some kind of digital method, multiplexing?

    What I am trying to find out is if it is possible to change the function of a certain switch, in particular the recirculating air button which I would really like to be the button that turned ON the cruise control instead of the awkwardly positioned one on the trim that is hard to find and distracting to be hunting for at 70mph!

    The switch itself seems to have only been used on early E39s (mine is 1997) and replaced by a switch on the wheel in newer models.

    If it is something in the wheel switches themselves would changing the wheel to mabe an M wheel be possible and solve the problem.

    If I can't find a solution to this problem I intend to put a foot switch b the foot rest somewhere, just to make it easier and safer to switch the cruise on.

    Any ideas or info will be appreciated.

    Thanks........Al
     
     

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    #2
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    It is multiplexing, if I have time tomorrow I will post up some really tech stuff to baffle you with.
     
     

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    #3
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    Quote Originally Posted by Ronnie View Post
    It is multiplexing, if I have time tomorrow I will post up some really tech stuff to baffle you with.
    Hi Ronnie,

    That would be great mate, well I "think" it would anway. hehehe

    Seriously it sounds cool, I have some electronics knowledge, not a genious by any standards, but I have made the odd circuit and used PICs etc.

    Thanks.....Al
     
     

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    ...and don't forget to include the transmitter module in you explanation Ronnie
     
     

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    Dawn (18-04-2009)

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    Here you go then, quench your thirst with this http://www.jaroslavklima.com/blog/20...ing-wheel.html
     
     

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    Dawn (18-04-2009)

  10. Getting somewhere 
    #6
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    Hi Ronnie and all,

    Thanks mate, that makes sense to me, seriously!

    Next problem is finding the whereabouts of the receiver, i was hoping perhaps stupidly that the reciever would be somewhere near the steering wheel so I traced the wires as far as I could without a major stripdown and haven't found it yet.

    I will be having a more serious look on sunday or monday weather permitting, unless someone can tell me the location.

    Thanks again Ronnie.......Al
     
     

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    Have a look here, http://www.bmw-planet.com/diagrams/r...9old/index.htm

    You will need Adobe SVG and Java downloaded/enabled.
     
     

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    Dawn (18-04-2009)

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    #8
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    Hows this, from a US car



    ScreenHunter_35.jpg
     
     

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    Dawn (18-04-2009)

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    #9
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    Cheers Ronnie,

    I will be doing some digging in the dash this weekend then! heheh

    Al
     
     

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