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Multiplex circuit question...

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Rescue1

Member
WOW... :shock: ...This is a great site.I have a question regarding a multiplex circuit I am trying to figure out.The circuit is from my 2004 dodge Ram where there are steering wheel controls that control assorted functions of the stereo.There is a single wire that I have found at the back of the radio where I see (what I believe to be) the multiplex wire with my fluke meter.I haven't tried a silly scope meter yet.I havent played with multiplex circuits to much so I am not sure where to start.Will a scope give me a baseline as to what type of multiplex circuit it is?How do I "tap" into it so I can get a solid voltage with two particular buttons?Is there a website on the subject where I can get the basics down for multiplex?I am sure I can go right to the switch for a solid voltage,but I like to do things the hard way,and furthermore have always wanted to figure out multiplex circuits.The car manufacturers are going the way of multiplex to save wire,so it will be nice to know.......Thank you for the help...... :?
 

Exo

Active Member
Is it a single wire? or a cable containing multiple wires?

If there's only one or two wires chanses are they use somekind of serial connection.
 

Rescue1

Member
Thank you for the reply.It is a single wire going to the back of the radio.I am not to knowledgable in the serial circuits.If in fact that is what it is, would I need an A/D converter to get a solid output.I could be on the wrong path,but I am assuming that each button will momentaraly output a different voltage.I could be wrong,thank you ahead of time for the help... :?
 

Exo

Active Member
Yes, outputting a diffirent voltage for each button could be what they use.
If this is the case, you should be able to just measure the voltage with your multimeter when you press a button.

But, it could also be a serial connection on wich information about the button pressed is sent digitally, one bit afther another. If this is the case then it gets more complicating. First you would need to figure out the protocol (How is the data formatted, how fast, ....) and if you want to manipulate this kind of connection yourself you'll need a microcontroller.
 
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