Is there any way to reduce the number of pins required for HDMI? - Page 1
Forum section: electronics / beginners

author: Marmotta
author_rank: Contributor
timestamp: July 20, 2016, 11:31:21 pm
content: I was planning on installing a Hi-Def HDMI board in a French Nintendo Entertainment System and convert the existing RGB output and cable to HDMI in order to not have to install an HDMI port on the back of the console. I remembered/hoped there being more pins on the existing output, but unfortunately there are only 10. Does anyone know if there's anything out there like a shift register or something that can reduce the required number of pins for HDMI?Alternatively, how can I reduce it to the pins that are strictly necessary? Will combining the shielding create too much interference? Are things like hot-plug and 5V required for all applications?

author: rstofer
author_rank: Super Contributor
timestamp: July 20, 2016, 11:54:59 pm
content: If you already have RCA type connections, why not just get a valid converter?http://www.showmecables.com/product/Component-Video-and-RCA-Audio-to-HDMI-Converter.aspxThere are lots of these things around.

author: Howardlong
author_rank: Super Contributor
timestamp: July 20, 2016, 11:56:41 pm
content: I don't know the system you're talking about, but RGB is analogue, bandwidth in the 10s of MHz, whereas HDMI is digital, bandwidth in the GHz.It's not a simple copper transition or even a level or balun translation. You need sync separators, high speed ADCs, one for each colour, high speed differential line drivers, clock signal, plus an I2C channel.There are small boxes that do RGB to HDMI reasonably cheaply.

author: Marmotta
author_rank: Contributor
timestamp: July 21, 2016, 12:30:51 am
content: The console will be modified and outputting HDMI, I'm not intending to convert RGB to HDMI, I just want to use the existing port on the back of the console which will be completely rewired on the inside, but as it was originally RGB SCART it only has 10 pins.

author: Signal32
author_rank: Frequent Contributor
timestamp: July 21, 2016, 12:42:45 am
content: Quote from: Marmotta on July 21, 2016, 12:30:51 amYou do know that if you do that you'll have to create your own custom HDMI cable adapter from RGB SCART to HDMI, right ?Anyway you mentioned that you'dd be willing to use a shift register. While this is not possible, this means that you're willing to have an external "decoder box"after the signal leaves the console.So why have RGB->HDMI->Shifted HDMI->HDMI->TV instead of just putting the RGB->HDMI converter outside of the console and only having RGB->HDMI->TV ?Anyway there are no real practical solutions to your issue, it would be much easier to just install an HDMI outlet.PS: If I were you I would probably just make a hole in the case and epoxy in the female part of an HDMI cablehttp://www.ebay.com/itm/-/281201435115

author: Marmotta
author_rank: Contributor
timestamp: July 21, 2016, 01:14:16 am
content: Please forget RGB. This has nothing to do with RGB. The original connection on the rear of the console is RGB (actually shoddily converted composite), but there will be no RGB signal of any sort connected to it.I appreciate that installing an HDMI output would be the simple solution and it is already thede factosolution for this mod, but the point is that I wanted to avoid making holes in the case. And maybe try something new in the process.Perhaps it's best to totally ignore the scenario which this is needed for and just boil it down to:how many pins is it possible to get away with on an HDMI connection?After the 8 TX signals and ground (including the 4 TX shielding lines), what else is there that is absolutely necessary to create a basic functioning HDMI cable?

author: hamster_nz
author_rank: Super Contributor
timestamp: July 21, 2016, 01:21:43 am
content: At a minimum you need 8 pins for the data, the clock plus a ground (nine in total). True HDMI has a separate grounds for each data pair, for a total of 12). Connectors must be able to work at 250Mb/s to support lowest HDMI standard video mode 640x480.You you want to support EDID another couple is needed, with separate ground.If you want to support hot plug detection another pin is needed.All documented onhttps://en.wikipedia.org/wiki/HDMI

author: Monkeh
author_rank: Super Contributor
timestamp: July 21, 2016, 01:26:26 am
content: Quote from: Marmotta on July 21, 2016, 01:14:16 amAssuming you have no expectations of it working reliably? 12. Maybe.Couple an inappropriate connector with hand-made wiring and the lack of proper grounds.. I wish you luck.

author: ConKbot
author_rank: Super Contributor
timestamp: July 21, 2016, 01:48:24 am
content: Could you fit a hdmi to micro hdmi or mini displayport cable inside the unit and have that socket mounted where the original socket went? Then use an appropriate cable to go back to full size hdmi. The adapters are just passive wiring adapters, but with the right kind of twisted pairs, shielding and impedance to make sure it all plays nice.

author: Marmotta
author_rank: Contributor
timestamp: July 21, 2016, 01:52:42 am
content: Quote from: hamster_nz on July 21, 2016, 01:21:43 amThanks. I was just looking at your work on HDMI and it's pretty impressive, although most of it went over my headQuote from: MonkehThe only part that will be hand wired at all will be the end of the cable connecting to the console, the other end of the cable will be properly crimped and I'll be making a PCB for the console connection, as the AV out and power input are on their own small daughter board which will be replaced. I have zero expectations of it, so I can't be disappointed. Worst that can happen is it won't work; I'd rather give something a try than assume it won't work and not bother.If it does fail, I will probably replace the current AV out with one from a Wii console, which seems to be a similar size and has 18 pins, so should be much less problematic.