Rockbox mail archive
Subject: Re: Still Problems with AJB Remote
From: [IDC]Dragon (idc-dragon_at_gmx.de)
> Due to the fact this output is configured as serial UART TX line, it is
> possible to have a open collector configuration of that uC port.
> My uC is powered with 5V and as I know the JB's have 3.3V.
Can't you power the Atmel with 3.3V as well?
> Ok so far - now the problem:
> If I connect a open collector transistor stage (just to not power the JB's
> input with 5V) between uC TX line and JB remote pin, the serial remote
> commands are accepted by my Studio Player, but not with Recorder's (none
> of them).
Such a transistor stage would invert the signal. I guess the average
erceiver is not happy with that... ;-)
> Sophana told me once to simply use a 10k resistor and connect it directly
> from my uC's UART pin to the JB's remote pin.
I can't recommend that, because it weakens your ability to pull the pin low.
The Archos has an internal pull-up on the remote input, which I have seen
being either 1 kOhm or 10 kOhm.
If you use the pin just as an input (not bi-directional), I'd recommend to
use a schottky diode to "emulate" an open collector. The diode will allow
your Atmel to pull the pin low, current flowing out of the remote pin. But
it will prevent your Atmel from driving it high up to the 5V level. Instead,
the internal pullup will take care of the signal going up again.
> Does anybody know, what are the differences of the remote input circuit
> inside the Studio Player's, old Recorder's and newer Recorder's (like V2)
Thare should be none, except for the strenght of the pullup.
> Maybe anybody has a schematic ?
See the ducumentation pages.
> Does anybody know a universal circuit to drive the remote pin, that works
> with ALL models ?
The universal bidirectional solution is that circuit with a MOSFET
inbetween, preventing the voltage to rise above 3.3V. I once posted that, am
too lazy to dig it out right now.
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Page was last modified "Jan 10 2012" The Rockbox Crew