[mythtv-users] HOWTO: change the channel on a Scientific Atlanta
Explorer digital cable box through USB port
cedric at phreaker.net
Wed Aug 11 23:56:34 EDT 2004
Hi all -
Thought some folks might be interested to know I that I have a working
solution for controlling the channel on a Scientific Atlanta Explorer
cable box through the USB port. The model I happen to have is a 3250HD,
and I have tested it on an 8000, but I suspect it will work on any SA
cable box with a USB port
warning: this solution is relatively expensive (US$100-$180), but I
figured some people might be interested just the same...
After two months trying to get LIRC to control my SA cable box with
three different off-the-shelf IR transmitters, I was about ready to give
up hope. That's when I ran across an offhand comment about somebody
witnessing their cable installer using a USB keyboard to change the
channel on their Scientific Atlanta cable box. Turns out many of
Scientific Atlanta's Explorer series of cable boxes have a USB port that
allows you to change the channel with a USB keyboard. Simply plug the
keyboard in, type the digits for the channel you want and the cable box
changes the channel. Sounds simple enough, but the tricky part is
generating USB keyboard signals from your Myth box. You'd think this
would be trivial, but it's not. If you want all the nitty gritty
details, read up on how the USB master/slave relationship works
(http://www.linux-usb.org/USB-guide/c15.html). Essentially, the problem
is that both the Myth PC and the SA cable box have USB "host
controllers", and you can't have two host controllers talk to each other
directly (yes, there are such things as USB host-to-host cables, but
they're hard-wired to act like network adapters, not keyboards).
So, we're left with the problem: how do we get our Myth PC to look like
a USB keyboard from the cable box's perspective?
Enter the "Vetra Systems VIP-335 SmartPipe"
(http://www.vetra.com/335text.html). Essentially a protocol converter
which takes ASCII characters on its RS-232 serial input and outputs them
as PS/2 keyboard codes. Slap on a PS/2-to-USB keyboard converter, and
you've got a serial-to-USB keyboard solution. Basically any characters
you send to the serial port appear on the keyboard output as if they
were typed on a physical keyboard. This makes the channel changing
echo `printf "%03d" $1` > /dev/ttyS0
I've been using this solution on my myth box for about four days now and
except for the initial connection, it has worked flawlessly. In order
to get the thing running the first time, I had to "hard boot" the cable
box (by way of disconnecting and reconnecting the power cable), and
connecting a real keyboard to the "passthru" port on the VIP-335 (and
hitting a couple number keys). After that, I was able to disconnect the
physical keyboard from the VIP-335. Since then I have rebooted the Myth
box and turned the cable box on and off (by way of the power button)
many times and it has continued to work perfectly. I suspect that I may
have to go through the song and dance with the physical keyboard again
if the cable box ever loses power completely, but I figure that isn't
going to happen too often.
For anyone using this as a HOWTO, I should mention that the VIP-335
ships with "data translation" turned off. Before you connect everything
for the first time, you need to turn data translation mode on by
flipping DIP-switch #4 up.
_Costs and other considerations_
As I said, this solution can be relatively expensive. The VIP-335 sells
for US$100 for the bare electronics or $150 if you want it all packaged
up in a nice black box enclosure. Add $10-$20 for a good PS/2-to-USB
keyboard converter if you don't already have one.
Looking at the Vetra website I see that they are now offering what
appears to be a version of the 335 that outputs USB keyboard codes
directly (http://www.vetra.com/335Utext.html). This unit wasn't
available when I ordered my VIP-335, but I suspect it would serve just
as well. The USB version is more expensive than the PS/2 version ($109
for the bare PCB, $179 for the box-enclosed version), but you would save
a couple bucks by not having to buy a PS/2-to-USB keyboard converter.
Anyway, that's my solution.
Be warned: If you try this, you do so at your own risk! I make
absolutely no guarantees of any kind. I'm not telling anybody to go out
there and buy one of these things, I'm just explaining what I did. What
you do with the information is your own affair. I am in no way
associated with Vetra Systems, Scientific Atlanta, or Earl's Pub on the
corner of 8th and Olive. No electrons were harmed in the making of this
email. Do not fold, spindle, or mutilate. Objects in mirror are closer
than they appear.
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