Design 360 HDMI with commercial Slip Ring - Page 1
Forum section: electronics / beginners

author: zeta799
author_rank: Newbie
timestamp: August 28, 2023, 07:33:07 pm
content: Hi, I am currently trying to build an HDMI cable using a MOFLON model MMC397 slip ring, I have tested continuity in each connection and I have not had problems, but the signal is not transmitted correctly since no image is seen on the screen, which suggests that it may be?, I have a Siglent oscilloscope available but it's up to 100MHz as I don't normally work at high frequencies so I can't directly analyze the signals. I attached pictures testing the female connectors on breakout boards without problem with a short cable section.Best,Sebastian

author: PlainName
author_rank: Super Contributor
timestamp: August 28, 2023, 07:55:24 pm
content: HDMI is very sensitive to matched signals and impedance. Being digital you only need a bit error or two to have whole block of data discarded, so you tend to get either a good block or nothing, unlike analog TV where the picture just degrades gracefully.

author: BrianHG
author_rank: Super Contributor
timestamp: August 28, 2023, 08:15:25 pm
content: With what I see, and I mean 'maybe', like a fluke of nature, you may get 480p@60hz working through there as it is only a 270MHz HDMI signal. 640x480x60hz is a 250MHz DVI signal. 1080p@60hz is a 1.485 GHz signal, so, dream on.Also, try shortening your soldered lead wires to the minimum and make sure the twisted pair data and clock signals are adjacent pairs on the rings with frame ground ring conductors inbetween. Otherwise signal crosstalk alone will make this impossible.

author: BrianHG
author_rank: Super Contributor
timestamp: August 28, 2023, 08:20:32 pm
content: Have you looked into a 3GHz SDI setup. It is a coax with 1 conductor for the video. The displays or video converters exist, but you need a special slip-ring designed for RF. The advantage is 1 single power, plus the 1 coax data line. Converter boxes from HDMI<->SDI and back exist, but keeping things cheap means only 1080p as 4k 12GHz SDI is still very expensive.

author: ArdWar
author_rank: Frequent Contributor
timestamp: August 29, 2023, 10:27:39 am
content: Due to the way most slip ring are constructed, and that HDMI signals can have components in GHz range. There's almost no doubt that you made an unintentionalRF transformer/filter/resonator/null/whateverdepending on the exact geometry the wipers happen to be connected.

author: wraper
author_rank: Unknown
timestamp: August 29, 2023, 10:40:29 am
content: IMHO the most viable way is fiber optic slip ring combined with fiber optic HDMI converter or modified optic HDMI cable.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 29, 2023, 11:02:29 am
content: Quote from: BrianHG on August 28, 2023, 08:20:32 pmYou may be able to use a rotary transformer with SDI - the sort of thing used on VHS head drums. or maybe even capacitively couple it across teh rotating joint

author: BrianHG
author_rank: Super Contributor
timestamp: August 29, 2023, 04:55:58 pm
content: Quote from: mikeselectricstuff on August 29, 2023, 11:02:29 amYes, with a SDI transmitter 1 foot from the slip-ring and the receiver within a foot on the other side, being a standard which transmits video for 100m cable runs and the receivers having a cable-length equalizer IC which amplifies and corrects the RF spectrum like a weak radio IC, a transformer / capacitive couple could work. Again, shielding here would be the key. Having to deal with 1 signal instead of HDMI's 4 balanced paired signals which all require equal timing length offers a greater chance of success.HDMI, ok with shielded cable, I have managed 25 feet, or 8 meters, but in no way can HDMI run down a 100 meter cable like SDI, it wasn't designed for it.

author: themadhippy
author_rank: Super Contributor
timestamp: August 29, 2023, 05:29:43 pm
content: Another way is hdmi-cat 5 convertor and cat 5 slip rings,not a cheap option,nor are you going to be getting 4k.

author: Kim Christensen
author_rank: Super Contributor
timestamp: August 29, 2023, 05:34:40 pm
content: Can I ask why you'd need continual rotational capability? Rather than just 360 or even 720 degree and then "unwrap"...

author: tooki
author_rank: Super Contributor
timestamp: August 29, 2023, 09:40:13 pm
content: Quote from: zeta799 on August 28, 2023, 07:33:07 pmThat it worked with the short jumpers is already very lucky. HDMI is a very high speed connection, so the data lines are 100 ohm differential pairs (which you didn’t do) with length matching restrictions ±5%, maximum 3mm).A slip ring that’s good for the GHz+ signaling of HDMI is probably an engineering impossibility. I can see it being done for a single coaxial cable, but not for a 19-pin connector.