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Subject: Re: BMW IBUS <-> Archos Jukebox (as CD Changer)
From: jobarjo (jobarjo78_at_yahoo.fr)
Date: 2004-03-17


----- Original Message -----
From: "Fernando Birra" <fpb_at_di.fct.unl.pt>
To: <rockbox_at_cool.haxx.se>
Sent: Wednesday, March 17, 2004 1:27 AM
Subject: Re: BMW IBUS <-> Archos Jukebox (as CD Changer)

> Hi,
>
> I remade the circuit with just one transistor and it is working well as
long
> as the pullup resistor on the (simulated) bus is at least 10K. For 5K the
> archos fails to put the bus low but it still can receive. It is definetely
a
> limitation on the current that the archos can sink per pin. At 1.2V (which
> is what I measure) the current is 8mA (by the SH spec). Now, with a pullup
> in the car bus clearly around 1K (or even lower, since the specification
> says that each node in the bus is required to sink at least 40mA and a
> maximum of 100mA should be possible in the worst case) what can I do to?
Can

1k at 12v make 12mA, which may be too much for the archos.
Are you sure the archos fails to put the bus low with 5k at 12v? it makes
about 2mA, which should be largely possible.
This should be caused by your mosfet that cause a voltage drop...

> something (transistor?) be placed at the archos pin that turns on when the
> pin gets low and whose primary function is to divert the current that is
> coming from the IBUS and sink it to the ground? I guess what I needed
would
> be something that would sink 80% of the current that is coming from the
> drain to the source of the MOSFET avoiding it to enter the archos pin...

it is possible but you will loose the bidirectionnal feature.
You need to use 2 wires: one for output driving a transistor pulling the
bus, and another one listening to the bus (behind your mosfet)

>
> If this is stupid or unrealizable then I guess I will have to make the
> serial mod and use some real IBUS transceiver like the Melexis 3122
chip...

no need for a transceiver a simple npn, a resistor and your mosfet should be
ok
but need 2 wire...

>
> Thank's for all your help Jörg,
> Fernando Birra
>
> "Fernando Birra" <fpb_at_di.fct.unl.pt> escreveu na mensagem
> news:c349m5$5e5$1_at_sea.gmane.org...
> > Hi,
> > "[IDC]Dragon" <idc-dragon_at_gmx.de> escreveu na mensagem
> > news:30726.1079351717_at_www29.gmx.net...
> >
> > > Do you have access to a different meter?
> >
> > I can try to get another one.
> >
> >
> > >Why do you have 2 transistors? Can this work? My suggestion was to do
it
> > >like the left part.
> >
> > Curiously, just using the left part doesn't work in my setup at home...
> >
> > I'm gonna do some more testing with different resistor values but this
is
> > getting really frustrating as it is all that stops me from putting the
> > archos in my car :(
> >
> > Fernando Birra
> >
> >
> > _______________________________________________
> > http://cool.haxx.se/mailman/listinfo/rockbox
> >
>
>
> _______________________________________________
> http://cool.haxx.se/mailman/listinfo/rockbox

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