[s-cars] CD changer interface questions

Paul Gailus gailus at mindspring.com
Thu Dec 23 23:28:24 EST 2004


There is a 2-wire serial data interface to communicate between the
Blaupunkt head unit and the changer interface unit. The two pins on the
head unit are labeled SCL (serial clock) and SDA (serial data).
So I strongly suspect that this is an I2C (I-squared C) data bus because the
clock and data lines are also called "SCL" and "SDA" in this 2-wire bus
standard.

I don't know anything specific about how the software in the head unit
and changer do the control. You could selectively disable this serial
interface
(with relays or transistors, etc.)  before going into CD mode when using
your
mp3 player. However, if you do this then it's possible that the head unit
won't
use its audio line inputs even though it's in CD mode, because it isn't
getting
the proper communications from the changer. You'll probably also get an
error indication on the display. But it still may be worth trying it out
anyway.

Paul

----- Original Message -----
From: Kevin Day <kday at ultrameta.org>
To: <s-car-list at audifans.com>
Sent: Wednesday, December 22, 2004 12:05 PM
Subject: [s-cars] CD changer interface questions


> Does anyone here know any details about the CD changer interface?
> Specifically,
>
> - How does the head unit know there is a CD changer present?
> - How does the CD changer know that the head unit is in CD mode?
>
> The reason I'm wondering is twofold. Firstly, I have an mp3 player
> connected to a relay (via its amp remote output) which selects between
> CD changer audio and mp3 player audio. This works fine, but when I'm
> listening to mp3s (nearly all of the time) the CD changer is playing,
> switching CDs, etc. It would be nice to avoid that wear and tear. The
> second reason is that my power antenna keeps jamming, and I'd like to
> gate the power antenna signal with an inverted 'CD mode selected'
> signal. I.e. don't raise the antenna when the head unit is in CD mode.
>
> This is for the 10 disc Gamma system.
>
> Thanks.
>
> -Kevin
> '94 S4
>
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