Volume Control on HUs, their operation.

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Currently I'm using an OEM head unit as my source. It has a connection to an Dashboard mounted volume control which I treasure for its convenience. I am contemplating changing the OEM to an aftermarket MP3 unit, but would dearly loveto retain the volume control.

I have looked at the OEM unit and the Vol UP and Down is controlled by two momentary lines that short to chassis ground for volume increments.

Has anyone ever looked at the schematics of HU, the volume control circuits and know whether or not I can adapt them to my ondash control? For starters, I would have to look at the units that have a separate vol up and down buttons.
 
It'll vary greatly by the aftermarket unit. Some use a direct pot, and that won't be easy to convert, unless it's motorised, and the deck has a remote control.

2 lines shorting to ground sounds like a motorised pot to me, although it could also be for a pushbutton volume control.

Don't buy a deck with adetatchable face. That's going to limit your choices drastically, practiucally all of hte units that I've seen have detatchable faces. The same goes for the "flip face" idea. You need something with the volume control as part of the deck chassis to have any hope at all of wiring in your volume control.

You'll also have to void the warranty and LOOK inside the deck. If it turns out to be impossible, you're stuck with it.

Anything with a pushbutton volume control could be wired in. It might take a couple of relays to make the signal what you want, but at that point it could be done. Similarly a motorized pot could be made to work. (If the deck has a remote control, you ought to be able to do it.)

Note: Depending on the way that the volume circuit is wired, it may be possible to severely damage your head unit. You could have a short circuit in some cases if (for example) you press "volume down" on your control, and "volume up" on the remote or the deck face. Such damage will NOT be covered under warranty (Which you've voided anyway)

Really, the remote control for aftermarket deck is a much easier idea to implement, although it can be done.

UrSv: I fond your comment ironic, considering yoru signature. :)
 
Here in the uk most branded hu's have a facility to link into OEM steering wheel controls and displays. I asssumed you'd have them over there. Or am I missing the point when you say mp3 and you're actually trying to link an i-pod or similar to steering wheel controls?
 
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