VGA over Cat5

Friday 30 May 2014 at 12:49 pm

Regular listeners will know I like using Cat5 cable (of which I have an inexhaustible supply of scrap lengths), so having successfully used it for audio, I thought I'd look at video too.

It's for a work project - we have a number of digital signage screens running on the excellent Xibo open-source system.  4 of our screens run off one client PC using a splitter/transmitter system from Mauve, left behind from the original installation, but these rely on a single Cat5 run between transmitter and receiver.  Other client displays use an old re-purposed laptop running Windows 7 ThinPC (a cut-down version of W7), which can be hidden in a suspended ceiling above the displays.

For the new installation we have no suspended ceiling, and no way of running Cat5 back to the transmitter, so it needs another old laptop, but there's nowhere to hide it.  There's a network point near the screen, connected back to a switch cabinet.  So, I thought, if I can put the laptop in the cabinet, and run VGA over the ethernet cable, then job's a good'un.

So I did a bit of Googling and found this on Instructables.  Could it possibly work?  Well, the answer is YES!

Got an old VGA male-male cable and cut it in half, then had to use a multimeter to work out which pins are connected to which wires.  (Caution - cheap thin VGA cables are somehow different, and combine some of the connections, so make sure it's a nice thick one).  The diagram on Instructables is viewed from the rear so is back to front, so watch that, too.  On mine the wires were as follows and connected to the Cat5 thus:

VGA Pin	VGA cable	Cat5 cable
Pin1	Red+	Solid Green
Pin2	Green+	Solid Orange
Pin3	Blue+	Solid Blue
Pin4	NC	-
Pin5	Black	Blue/White (with Pin8)
Pin6	Red Screen	Green/White
Pin7	Green Screen	Orange/White
Pin8	Blue Screen	Blue/White (with Pin5)
Pin9	NC	-
Pin10	NC	-
Pin11	Brown (not used)	-
Pin12	NC	-
Pin13	Orange	Brown/White
Pin14	White	Solid Brown
Pin15	NC	-

Spliced together (sorry, I sealed before photographing) with plenty of heatshrink it looks like this:

Make 2 of these!

Then I tested using another bodge job - a 20m extension cable with a pair of cat5 cables and boxes we use for emergency networking.

And bugger me, it only works!  1024x768 is what we'll be using, but it did 1280x1024 fine too.  There's a little bit of ghosting, but for text on a screen, it's perfect.

I'll update when it's actually in situ and working across what will be Cat6, in fact.