[mythtv-users] IR Blaster - pin 7 instead of pin 4?

[Robin Gilks]

[snip]
> I found that instead of using pin 4
> (DTR) as the transmit pin, it is actually pin 7 (RTS) that is toggling.
> When measured against pin 5 (SG), it displays a negative voltage.
> (Approaximately -11V).  I put Andy's  change_chan.sh script in a loop to
> keep the channels changing and measured the pin voltages.  Pin 7's
> voltage starts fluctuating.  On my digital meter, it looks like it jumps
> between about -9.5V and -11V.   As soon as I stop, it returns to a
> steady -11V.  I'm quite sure this is the pin that is being controlled.
> I am attempting to drive the pin using the DirecTV codes from
> http://lirc.sourceforge.net/remotes/directv/G051204 in my LIRC file in
> place of Andy's Motorola box codes.  I'm fairly certain the
> configuration is correct.  It almost appears as if the lirc_serial
> control is driving the incorrect pin, but I have no idea why that would
> be.

If the IR blaster were being driven by pin 7 then that pin would be going
from -11 to +11 - RS232 voltage swings are symmetric (within the bounds of
circuit loading) about zero.

I think what you are seeing is the voltage changing slightly because
another port or pin is taking current and making the RTS pin you have been
monitoring bob up & down a bit.

Things to check:
1. Is pin 4 doing anything
2. Is pin 4 of another port doing something
3. Are there any indications in the log of a failure to load the serial
driver for lirc (perhaps due to the internal driver not being turned off
by setserial).

Its not a mother board that has the 1st serial port reserved for some
internal port, modem, mouse or something like that?

Hopefully this will give you some clues...

-- 
Robin Gilks