Rockbox mail archive
Subject: Re: BMW IBUS <-> Archos Jukebox (as CD Changer)
From: Fernando Birra (fpb_at_di.fct.unl.pt)
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
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...
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...
Thank's for all your help Jörg,
"Fernando Birra" <fpb_at_di.fct.unl.pt> escreveu na mensagem
> "[IDC]Dragon" <idc-dragon_at_gmx.de> escreveu na mensagem
> > 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
Page was last modified "Jan 10 2012" The Rockbox Crew