[mythtv-users] HOWTO: change the channel on a Scientific Atlanta Explorer digital cable box through USB port

[Cedric Tefft]

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 
(http://www.scientificatlanta.com/products/consumers/index.htm).  Fair 
warning: this solution is relatively expensive (US$100-$180), but I 
figured some people might be interested just the same...

_Background
_
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?

_Solution_

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 
script trivial:

#!/bin/sh
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.

_Standard Disclaimers_

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.

__
- Cedric


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