[mythtv-users] How can I change channels on a Cisco HD271 DTA (with TWC)?

[Mike Perkins]

On 11/06/15 20:02, Hika van den Hoven wrote:
> Hoi Gary,
>
> Thursday, June 11, 2015, 8:40:50 PM, you wrote:
>
>> On Thu, Jun 11, 2015 at 4:47 PM, Ed Clark <eaclark at ameritech.net> wrote:
>> ....
>>> Being a bit of a noob, I'm looking for suggestions as to how
>>> to determine what IR signals this remote is sending.
>
>> Never seen one of the 271's, but most of these DTAs
>> use the XMP protocol.  I suspect that one of the recent
>> Cisco XMP definitions in lirc will likely work, or try the
>> MotorolaDTA100-PaceDC50X one which worked on
>> previous gen DTAs (and shares most of the same
>> codes).
>
>>> Furthermore, what I'd ideally like to do is run a audio patch cable
>>> from the line out of the backend to the backend to the IR IN of
>>> the DTA.  Then, hopefully, I'd just play the appropriate WAV file to
>>> get the equivalent button press.  Thus skip using an IR blaster.
>>> But, that may be a pipe dream...
>
>> Likely a pipe dream.  IR bitrates are above the typical
>> audio reproduction levels (30-70 kps) (and then the sampling
>> multiplier for a wav file).
>> .
>> The typical solution is an ir blaster, and for the fancy,
>> an appropriate cable between your blaster and the ir
>> input on the DTA (for the paranoid, such as myself,
>> with an optical isolation ic in the middle).  I seem to
>> recall some being sold online, typically for TiVos, and
>> for the build it yourself crowd, various examples are
>> around.
>> _______________________________________________
>
> I have no experience with this, but my logical thinking would suggest
> that you could leave out the ir part between the blaster and the DTA,
> sending the electrical signal straight from your com port to the
> IR-IN-jack. You off cause have to know the wiring and the protocol. You
> then can load lirc-serial pretending there is a blaster connected.
> Then if you give a send command to lirc the DTA wouldn't know the
> difference.
>
> Has anybody tried this?
>
You can't directly connect the output of one with the input of the other since 
the DC levels may be different and you'll end up with the black smoke coming out.

That's why the previous reply suggested an opto-isolator. Basically this is an 
LED 'blaster' and an optreceptor built into the same package for exactly this 
kind of operation where you can't be sure about electrical compatibility.

Opto-isolators are basically 4- 5- or 6- pin chips which are cheap and 
(relatively) easy to find in an electronic store - or online, of course. Wiring 
up each end shouldn't be difficult if you are familiar with a soldering iron.

-- 

Mike Perkins