[mythtv-users] help with channel changing

Michael T. Dean mtdean at thirdcontact.com
Sat Dec 17 12:42:20 EST 2005

sarvinc at fastmail.fm wrote:

>Is there another card I can buy to skip the IR blaster step?
>I know this sounds crazy but the TiVo does not use an IR Blaster. In fact it will change the channel even if it's only connected to the TV via coaxial cable. I don't see how and I'm still in awe. Maybe it's magic? Maybe my TV has something to do with it.
Some digital cable boxes provide a serial port connection you can use to 
change channels.  Others have a firewire port.  Others require you to 
change channel using buttons on the cable box or using an IR signal (i.e 
the remote provided by the cable box).  It is impossible for an external 
device to change the channel on its own (i.e. it must ask the cable box 
to change the channel) because the cable company is transmitting the 
signal in a proprietary encrypted format that only their cable boxes can 
tune.  Therefore, getting another card won't help.

If the cable box supports serial or firewire, you could hook those up.  
Note, however, that it's very unlikely that TiVo is using either of 
these to change the channel.  When you say that the TiVo can change 
channels when it's "only connected to the TV via coaxial cable," I'm 
assuming you mean when the TiVo is not connected to the digital cable 
box.  If so, in that configuration, the TiVo is tuning using the analog 
channels which are also transmitted on the same cable connection (and 
you won't be able to get any digital-only channels).

Your TV should be completely independent of any channel changing 
functionality.  If using a TiVo or a digital cable box, the TV simply 
displays whatever you feed it via the S-Video/Composite connection.


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