Re: USB to serial confirmation

[Eric J. <al...@xm...>]

On Tue, 26 Oct 2004 19:07:07 -0700
Alan Dayley <al...@co...> wrote:


> I assume it won't work for one of two reasons:
> 
> 1. The Serial to USB adapter does not provide sufficient voltage for it
> to work.  If this is the case, would it be solved by using the low
> voltage version of the receiver?  (I hope.)
> 
> OR
> 
> 2. The LIRC driver directly manipulates the serial port hardware instead
> of connecting to the /dev/ttyS? device that would be provided by the
> Serial to USB adapter.  In this case, I am back to "this won't work." 


   All of the above. 

   If you had an irman type device - which decodes the ir signal before
sending it through the serial port - you could maybe find some way of
supplying enough power to it, and it would theoretically talk through the
usb serial port. I almost tried this once, with a Keyspan USB-28X, which is
probably one of the better usb serial devices. Instead i realized i had
another tv card laying about with an ir receiver integrated. 

   I don't know if anyone has ever actually tried this. If the irman (or
ira, or similar device) has a low-dropout regulator, you could tap
regulated +5v from a keyboard (or usb) port and it would maybe get enough
juice to function. You would be better off removing the regulator entirely
in this case, but the irman casing appears to be glued or fused shut. the
ira-3 looks like it can be easily worked on, but I've never actually held
one in my hands. 

   The majority of serial port ir receivers - including the home built, and
packard bell type, and I believe the zapway receiver as well - yes, the
lirc driver talks to the serial hardware directly. lirc_serial.o actually
requires that you either not load the serial.o driver or that you disable
much of it's functionality by executing 'setserial /dev/ttySn uart none'

   In any case, that style of receiver - which sends raw pulses over the
serial port - requires very tight timing, which isn't available on usb. 

   One caveat regarding usb serial - even if you have resolved the above
issues, I have observed that usb serial ports often do not behave like a
normal serial port, with regard to setting of control lines, and things
like that. I'm told that my Keyspan adapter is one of the better ones made
(integrated microcontroller and all), and it's a touch hinky with some apps
under linux. I don't recall the details, or what precisely i was trying to
do, but i did find one situation where the only way i could get an app to
work with it was by opening the serial port with minicom and then exit it
without closing the port.