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Subject: RE: introducing the car CD changer project (your opinion, please)

RE: introducing the car CD changer project (your opinion, please)

From: Andreas Stemmer <>
Date: Wed, 19 Mar 2003 18:43:59 +0100


I was thinking about such a project a few month ago (there was a heavy
discussion about possible bidirectional communication with the jukebox
on this list). It's funny, but only about two weeks ago, I decided to
start this project again. In my case, it's a Sony car radio that has to
be cheated. The Sony Unilink protocol is quite known and there's a text
display. Shouldn't be too much work, because there are already PIC/Atmel
projects on the web which can do the cd/md changer emulation. The
biggest problem was the bidirectional communication with rockbox so I
decided to start with a one way interface.

> We can say the technical issues are cleared, are now facing the MMI
> implementation. That's where we'd like your opinion.

I already spent some thoughts on this topic. Best solution for me would
be to predefine 6/10 playlists (my Sony has got 10 direct cd keys)
simulation the different cds/mds (your number 2). The 99 song limit only
exists for the displaying of the track number. You can go the the
next/previous song or choose another playlist.
I don't think full directory access is really needed. While driving,
it's very dangerous (if not impossible) to navigate through a complex
directory structure with such a display (the Sony can display 8 chars).

> Some more thoughts about car usage:
> - We'd like a seperate (fixed?) volume/sound set for car mode, so it's
> independent of how you used it last time when walking around.

The interface could send some "Hello, you're in the car" command at
startup which makes rockbox save the current settings and load a special
car.cfg. If there's enough time, rockbox could load the saved settings
at shutdown.

> - The adapter should allow a real changer to be connected
> behind and go to
> passive mode if no Archos is connected, so you can use your
> regular changer
> then.

No issue for my case, I simply use a sony source selector which allows
me to connect two changers to one radio.

> - Archos powerup is problematic. The adapter cannot switch it
> on, so you need to do that manually.

No, I tried the following: the interface will need power from the car
and of course you'll want to have some power adaptor for the jukebox,
too (a simple 7809 should be enough). Make the power supply for the
jukebox switchable by some port pin of the atmel. To start up your
jukebox, activate the power for the jukebox for one or two seconds. This
prevents the archos from going into charging mode. Instead, it will boot
rockbox just as if the on button was pressed. After fifteen seconds, you
can switch on power again to charge your batteries.

> - In case you can mount the Archos in a nicely visible
> position (e.g. with a
> mobile phone bracket) it would be useful to have a simplified
> display on it
> with a large font.

No problem with a car.cfg

I'm looking forward to your implementations. I'm sorry, I can't show you
anything yet.

Andreas Stemmer
Received on 2003-03-19

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