Friday, July 07, 2017

EDID will get you every time...

I was helping to configure a new board room. This one is a tiny bit different by having two nice big TVs mounted on the walls and the cable run to each is at least 30m. So - HDMI does not reliably go that far over copper cable (I know - somebody always has an example where they've made it work, but this has to be reliable!). It's probably why so many training/presentation rooms still have SVGA on the desk plate; it's reliable.
The other requirement was that with no operational changes you should be able to plug an HDMI laptop into the desk plate and " just works"!
So - Barnfind are my favourite fibre parts and so a couple of BarnMini03 & 04s with single-mode fibre between (spliced, of course!) takes the HDMI up to 80km. I used these nice wall-termination panels from ADC Krone.

I also bought one of those cheap no-name HDMI splitter/DAs from Amazon as I've had no trouble with them in the past - they even work well as HDCP removers. However in this case as soon as I plugged in the second TV the system would fall over with the "signal present" light on the DA going out - TV A or B could be fed individually but not together. Sticking the EDID analyser on the feed to the DA i/p showed the DA was generating and EDID exchange ever second or so and alternating between the two different EDIDs - first Mr. Sony then Mr. LG (different models of screens).

So, after a bit of head-scratching I put one of these on the input of the DA - it essentially answers EDID enquiries without forwarding them upwards. Works like a charm;

My next test will be to see if the DA pulling the hotplug detect pin low and triggering the erroneous EDID exchanges. For this I need to dig out one of my famous Root6 Spoof'o'matics which we had manufactured in quantity after a similar problem with Avid and how it reacts to different monitors.

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