LG UD4379 control via RS232 using C#

Recently I decided to upgrade my primary home computer monitor.  It had been 10 years since I bought my last monitor, a 24″ DELL, and its predecessor which is a 19″, that served as a secondary was bought a few years before that.   I went for what is one of the larger ones currently on the market, the LG 43UD79 .  This monitor has six inputs, four HDMI, one Display Port, one USB-C.

There are also eight ways you can configure the inputs.

  • Single input uses entire monitor
  • Singe input with PIP in either upper right, upper left, lower right or lower left (4 options total). PIP has a transparency setting to boot.
  • One input top half, one bottom
  • One input left half, one right half
  • Quad mode, with an input in each corner

You also get to choose which input sends sound to the built in speakers.

Taken all together, that is a lot of possibilities.  Furthermore, you can use the joystick at the bottom of the monitor to change inputs/arrangements, or use the remote control.  Now the remote control is useful, but it is still a bit of work.  Switching from a 4 input quad mode, to single input with PIP in the upper right, audio coming from the PIP source?  Lots of keypresses on the remote.

Luckily the LG UD4379 comes with an RS232 port, and I can write code.  So long story short I wrote a small C# program to handle switching from mode to mode.  I call the program from a set of shortcuts in a folder on my desktop, each named by what they do.

Main caveats so far :

  • Sound input can’t be changed via RS232 as far as I can tell, keep the remote handy.
  • Best to have another dedicated monitor to run the program as switching away will make the program inaccessible (you can’t see it).  Wasn’t an issue for me since I made my old main monitor the new secondary, dedicated to the PC that has the program installed.
  • Can’t change PIP transparency via RS232, but at least the monitor seems to remember it.

The code and hardware used can be found here on GitHub

Quad mode

Single input with PIP




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