[mythtv-users] LIRC initialization of serial port in MythDora 12.23

[Bob Shanteau]

Bob Shanteau wrote:
> Many years ago on another list, Thomas Breuer wrote:
>> The lirc_serial driver obviously sets RTS positive and DTR and TXD 
>> negative. So we can get a positive (as used in the standard circuit) 
>> and a negative supply.
> That's not what I am seeing on the serial port of my desktop computer 
> running MythDora 12.23.

I found my mistake. I found that I had reversed the wires to pins 1 
(DCD) and 5 (GND) on the DB9 connector. When I connected those wires 
correctly, the homebrew circuit works as advertised, at least for 2 of 
the 3 IR receiver modules I tested: Vishay TSOP39338 and the module in 
the irblaster.info receiver. But when I used a Sharp GP1U27, I found 
that I had to keep a button pressed to get a response.

Once I had corrected my wiring error, I remeasured the voltages to the 
other pins on the DB9 connector after MythDora boots up. This is what I 
found:

Pin 3 (TXD) +10.7V
Pin 4 (DTR) -10.6V
Pin 7 (RTS) + 8.8V

(The voltages on the other pins were negligible.)

Thomas Breuer said that TXD should be -10V, and I do get that initially, 
but early in the boot process the polarity switches to positive.

Bob Shanteau