multiple switches on one wire?

Discussion in 'The Projects Forum' started by MATTY B, Apr 22, 2009.

  1. MATTY B

    Thread Starter Active Member

    Jan 26, 2008
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    0
    Hey, I have a little project to figure out for my car and thought you guys could help me figure this out. What I need to do is put multiple switches on a steering wheel but the kicker is that I only have one wire to send the signals through the column. To eleborate, I can only use the horn contact because it spins with the steering column.

    Ford did this with cruise control functions on the steering wheel and each button had a resistor on it that switched to ground. So say switch one would have 5k ressitance and switch 2 would have 20k resisntance so on and so on. then on the other side of the wheel the module could tell which switch was pressed based on the resistance to ground.

    What I need is something just like this that can ground a series of normal automotive type SPST relays and have normal off the shelf miniature NO mom switches on the wheel.

    Im sure I could make a fairly simple circuit to do this but I dont have a clue what principle this is based on. Hopefully someone can point me in the right direction. BTW Im hoping to make this with just regular components and no programming or anything like that, just simple robust components that can differentiate the different buttons. Thanks.
     
  2. MATTY B

    Thread Starter Active Member

    Jan 26, 2008
    45
    0
    heres a general description of how it works on a Cobalt for steering wheel mounted controls, its the same basic function

    "The steering wheel controls are actually a resistor network which consists of multiple momentary contact switches and a series of resistors. The switches and resistor network is arranged so that each switch has a different resistance value. When a switch is pressed, a voltage drop occurs in the resistor network which produces a specific voltage value unique to the switch selected. These specific voltage values allow the radio to identify which switch has been pressed. The radio responds just as if the corresponding radio front panel button had been pressed.When the radio is ON, the radio supplies approximately 10 volts to the switches on the 10-volt reference circuit. The specific voltage signal from the switch is returned to the radio on the steering wheel controls signal circuit.This may inhibit the use of the redundant control with an aftermarket head unit."

    What type of circuit can differentiate the different voltages?
     
  3. wollybyte

    Member

    Apr 5, 2009
    15
    0
    one side you have resistors
    you can use a LM3914 to do the job on the other side
     
  4. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Like others have stated, this is a good application for an ADC. I would highly recommend looking into PICAXE chips, particularly the 08M. Learning to write code for it is a snap and the PICAXE Interpreter is free!
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,645
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  6. MATTY B

    Thread Starter Active Member

    Jan 26, 2008
    45
    0
    Yeah Im going to look into this!! I have always been deterred from PICs because I dont understand the programming part. Ive had a lot of ideas for parts that would definitely be easy to build if I used a PIC, now that I saw the editor and the ability to program it with a F'n flow chart Im sold.. I think this may be the stepping stone to me getting into programmable circuits. Thanks for the recommendation this will probably be the way I go with alot of my projects now,
     
  7. MATTY B

    Thread Starter Active Member

    Jan 26, 2008
    45
    0
    Just wanted to stop in and update this post. Thanks so very much for introducing me to the PICAXE!!! Before this micros were totally out of my realm of expertise (as was alot of electronic projects) but this chip has allowed me to do a ton of things that I would be able to otherwise.

    I highly recommend these to anyone as they are very easy to use and also damn cheap to boot. I not only got this circuit working, I also finally made a relaible and functional push button ignition switch that requires less than 15 components total.

    Once again thanks so very much I trully appreciate it!!
     
  8. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    I'm very happy to know that I introduced you to the PICAXE. Have a ball!;)
     
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