[mythtv-users] Possible to change channels via USB?

Rod Smith mythtv at rodsbooks.com
Fri Dec 18 05:05:04 UTC 2009

On Thursday 17 December 2009 01:28:31 pm Jeff Bryner wrote:
> I'm struggling with firewire off a dch3200. I can get it to change
> channels and stream, but sometimes it dies (one channel is fine, one
> is bad, back to first and it's fine, later it all fails).

I've run into some of that, too, but it tends to stabilize significantly in 
normal use, vs. testing use. It's also unreliable in live TV mode for some 

> How do you do just the channel change via firewire? I'm thinking it's
> time to revert to that and record via my pchdtv tuner card.

Here's my basic FireWire tuning script. You'll almost certainly have to change 
the video device file and/or its input, and the GUID for your cable box 
(0023eefffea7cda7 in the below). I've also had problems in the past with 
razzy audio from the tuner card, which can be gotten around by tuning to a 
regular (coax) channel, copying some data to /dev/null, and tuning back to 
the S-video input. I've commented out those lines below, but if you 
experience bad audio, you should uncomment them or try something similar. 
Note that the 3200ch script is my modified 6200ch program. The original 
6200ch comes with the MythTV source code, in contrib/channel_changers (or it 
did come with 0.21; I haven't checked the 0.22 source tree). I needed to 
modify it to recognize my Motorola DCX3200-M, but I think the DCH3200 was 
supported in the version I used as a starting point.

------------- FireWire channel-change script ---------------

# Script to change the channel on the cable box using FireWire

# Set the tuner to the coax input and copy some data from it....
#v4l2-ctl -d /dev/video-PVR500-1 --set-input=0
#sleep 1
#dd if=/dev/video-PVR500-1 of=/dev/null bs=1024 count=512

# Set the input back to S-video....
v4l2-ctl -d /dev/video-PVR500-1 --set-input=1

# Change the channel for the specified cable box....
/usr/local/bin/3200ch -g 0023eefffea7cda7 $1

Rod Smith

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