[mythtv-users] interfacing MythTV with a DTA, lirc queries

[James Miller]

On Sat, 23 Jul 2016, James Miller wrote:

>> One of my remaining questions regarding this DTA concerns the 3.5 mm jack 
>> on the back labeled "ir in." From what I so far gather, this is included to 
>> provide a means for Tivo systems to interface with the DTA by wire rather 
>> than by sending IR signals. Is there some way a MythTV system can interface 
>> with the device by wire using that 3.5 mm port? (see 
>> https://www.amazon.com/TiVo-Cable-Direct-Connect-Control/dp/B00VQWYNB8 for 
>> an example of a cable that is meant to connect a Tivo system with the DTA)
>
> To continue in the vein of discovering answers to my own queries, I see that 
> this issue of the "ir in" port on this DTA was also addressed on this list 
> about a year ago in the thread entitled "How can I change channels on a Cisco 
> HD271 DTA (with TWC)" 
> (http://lists.mythtv.org/pipermail/mythtv-users/2015-June/379485.html).

An update on the matter of the "ir in" port on this DTA. While recently 
researching IR hardware for a possible system modification that will allow 
me to once again record NTSC cable from a DTA, I ran across hardware sold 
by Iguana Works. On their site I noted that some of their USB IR emitters 
have, in addition to IR lenses, a 3.5 mm port. As they write on their site 
about the device "This version of the USB IR Transceiver has two 3.5 mm 
sockets: Socket A: transmits IR using an IR Emitter and supports up to two 
independent transmit channels when used with a stereo->mono adapter. . . 
." Being uncertain whether this might be something that could connect to 
my DTA's "ir in" port, I opened a support request to ask about that. Below 
is the response I received:

"Short answer: maybe, but probably not. Sadly 3.5mm port for "IR In" is 
not standardized. Typically, this port takes in the same 'data' as an IR 
receiver. However, Sometimes they want a demodulated signal and sometimes 
they want a modulated signal. Our output for wired emitters is a modulated 
out. If that is what the "IR In" wants, then you can connect our IR wired 
IR output to that input and it should work. However, often it wants a 
demodulated signal and it won't work. If it doesn't work, you should be 
able to use a wired emitter and place it close to the DTA's IR receiver 
and that should work."

That's not totally comprehensible to me (I do not understand modulated 
versus demodulated), and I'm not certain how I might go about determining 
which sort of signal my DTA's "ir in" port might want. Others on this list 
will undoubtedly understand better the issues involved. The take-home for 
me is that there is no guarantee, if I buy this device, that it will 
interface with my DTA as I'm hoping it would. In which case I'd need to 
buy an additional piece of hardware to go with it, namely, and IR emitter, 
going back to the strategy of just sending IR pulses to the DTA's IR 
receiver. But this seemed like information others might be interested in, 
so I thought I should include it in this thread.