Making an LG TV Controller from a Linux box.

A Stupid Linux trick...

Summary: I wrote a web page to control the LG 37LC7D TV via it's RS232 Port.

tv pic/logo

So I got a wild-hair one day to buy a new tv. So I took my wife to Best Buy and we looked at TV's. An awe inspiring selection made me briefly think that I should have researched it first to find the best, but screw it! I was there with money to burn! My wife hunted around and found the "open-box" TV's. These are TV's that have been returned for one reason or another. Usually they are much cheaper than the off-the-shelf models. So woot I found my "open-Box" 37" (about 1m diagonal) TV. It is an LG 37LC7D, with no remote. So we got it home and had dinner while I started pulling coax for Cable.

Poking around I noticed it had both an RGB in dsub15 port and a 9pin RS232 port. Ahhhh!!! In geek heaven I hunted on LG's website for a manual (Local Copy). Reading it, I found the section on the serial commands to send to the tv to control it. I instantly thought this is a job for LINUX!

I only had one spare machine, an old PII-350 that a friend had been throwing out. I snagged it, and I knew no fancy distribution should grace this box. I also knew the while I could probably do mythTV on it, I wanted the computer to control the TV not just the input to the TV. I needed functionality and stripped down power, Slackware called. Machine info. I have a Slackware subscription but the latest release got screwed in shipping(cracked case and crap on the CD's) and the previous release I have loaned out to a friend, so Slack 10.2.0 it was.

Basic install, added minicom (terminal client for testing the serial port), apache, and php. I added the apache user to the serial port group, "uucp", and gave it write perms to the serial port. I grabbed a 9pin serial cable and null-modem adaptor from a local radio shack (where the counter troll asked me if I was sure of what I was doing, HAH!). I had an old wyse-60 terminal that I was able to test things with as well. It was neat seeing the old amber characters come up, <sniff> call me sentimental.

Time for some programming. I went with php b/c I know it well, and I can program in it fast (and badly). I arranged each function to handle a specific task(duh) and only send it's specific function to the serial port.

Each LG command uses a specific format:

I could have made a giant class and functions building the eventual string to send to the serial port in one fell swoop. But that's for version 2. ;-) The tv does an echo back with a success code on the serial port, but I ignore the return codes... They can be used for error detection but since I write bug free code that's not a big deal. ;-)

So after some fiddling with the linux box in minicom & shell (turning off flow control to the serial port). There are two slight "issues", one, when you tell the TV to turn on it takes about 15 to 20 seconds. I should have some javascript or something to pause for that time before jumping back to accept user input. So a slight pause is needed. Secondly, the channel selection data string while correct, doesn't always change the channel. I'm not sure about this one, I am pretty sure I've gotten the format of the statement correct, but there seem to be breaks in the data range needed to be sent to the TV. I blame my programming (features not bugs!) for this one. I should probably read the manual again.

All in all it works well for changing the volume, turning on/off the TV, setting the channel. The TV is nice too. I like the selection of inputs. The picture is clear and nice. I've had X (The windowing system for those who don't know) up on it as well as DVD's from a real dvd player and from a PS2 and both look nice. The Transformers movie was awesome on the big screen. I think an HD Tivo is in my future now.

Future Features:
Needs channel up down for surfing
Since the channels are input to the serial port, an up/down channel control would mean keeping the old channel setting. This isn't a big deal but since my wife can also control the channels, her or my state information about which channel is on, could be different.
Needs Volume up down.
See the channel changing explanation above, this has the same problem. In practice though, this hasn't been a big deal.
Channel previews
I like this idea a lot (which means it should be implemented soon). I've got an Hauppagge TV card, I can stick in the computer. I would like to set it up then to grab a frame of video from each channel once every five mins, and then have that displayed on the page with the channel selection. This way I can preview what's on all channels b4 deciding to jump to one or the other.
Last viewed channel
Allow me to jump between two channels. Maybe even setup "channel sets", sets of channels to cycle between.

All in all, it's been a fun project, of course the "source" for what I did is here: lg_tv.tgz I release it under the GNU GPLv2. Here are some Pics of the finished "product":

Web Interface to the TV Controls
Desktop w/ web interface to TV

The Setup (TV on top, Computer on Bottom, Wyse Terminal making appearance)
the tv and computer setup

Back of the TV (with INputs EveryWhere!)
Back of the TV with cables

A Null Modem Adapter!!! (OK, not that exciting)
cables to the back of the computer

Well I hope you found this informative and even more importantly inspiring to let you do your own TV/Device/Toaster controlling linux box.

The web design on the TV interface was done by Helen at, all bad php coding was done by me.