Extending the walking range of the Rift (making cables long)

Longer cables means more latency, right?

"ftarnogol" wrote:
Longer cables means more latency, right?

No, essentially zero latency compared to software driver and sampling latency. This keeps coming up in the forums. Electricity travels at the speed of light in a vacuum, or about 66% of the speed of light in a coaxial cable.

HDMI cables need an active repeater every 50 feet. USB cables need a repeater (hub) every 15 feet. Such repeaters add almost no measurable latency. The latency of a 50 foot HDMI cable is measured in nanoseconds, and the switching time of an active digital repeater is also measured in nanoseconds.

Even wireless HDMI and wireless USB have almost no latency.

To put this "speed of light" issue into perspective, let's do a little thought experiment, using the following facts:
1) The speed of light is about 300,000 km/sec.
2) The distance from the earth to the moon is about 384,000 km.
3) Common coaxial cable has a 0.66 velocity factor.
4) The transit time (latency) for a signal to travel in a coaxial cable (such as HDMI) stretched from the earth to the moon is (384,000 km / (300,000 km/s * 0.66)) = 1.94 seconds.

So, not worrying about repeater delays (which may double the latency), to keep additional latency caused by HDMI cable length below one millisecond, we should not use an HDMI cable on our Rifts that is longer than the distance a swimmer would make for three round trips between England and France (34 km apart at the Strait of Dover).

Question: Did I get my calculations right?

Technically there's nothing stopping you from using wireless USB, wireless HDMI, and a battery pack for powering the three devices... but that's a heck of a mess to carry around. A backpack would probably be best. The Rift is 5v, so if you can find the right adapter, any USB battery pack would probably work.

There has also been some work to modding the Rift to pull power from the USB connection rather than the power jack; the Rift draws slightly more power than the USB spec normally allows, but most motherboards are willing to go a bit out of spec:

http://www.roadtovr.com/2013/04/18/oculus-rift-usb-power-hack-eliminates-need-for-a-wall-adapter-4971

EDIT: Caution, some wireless HDMI systems do add enormous amounts of latency, others don't. It depends on the standard and the implementation used.

"guspaz" wrote:
http://www.roadtovr.com/2013/04/18/oculus-rift-usb-power-hack-eliminates-need-for-a-wall-adapter-4971

EDIT: Caution, some wireless HDMI systems do add enormous amounts of latency, others don't. It depends on the standard and the implementation used.

Notice that the Rift featured in the USB power hack at that link belongs to an Oculus employee:

"At
TVs using HDMI can add a huge amount of latency. Some HDMI repeaters may add latency, but many do not add measurable latency (digital gate switching time measured in nanoseconds). Cables and connectors are also insignificant.

Assuming that the computer video card is programmed for minimal latency, and the Rift is designed for minimal latency, cable length is not an issue. However, some desktop LCD panels, and most HDTV sets, do often add (sometimes up to a second) latency (lag) between when they receive an HDMI signal and when they display it. They also delay audio to sync it to the delayed video. Here are some tips for preventing such latency:
http://www.televisioninfo.com/features/how-to-prevent-game-lag-in-3-easy-steps.htm
This would not be an issue for the person wearing a Rift, but may be valuable for audience members watching a Rift demo on an HDTV.

And yes, check out reviews of wireless HDMI devices before purchasing. Some good ones have been discussed in the forums here and at MTBS3D.

HDMI repeaters or amps mostly shouldn't add much latency, but range extenders that involve completely changing the format might if they buffer full frames. HDBaseT, for its part, claims to add zero latency, but that's not wireless (it's HDMI over a single Cat5e).

Hi all,

I am following this with the hope of extending the cable from the HMD to the control box.

I found the teardown of the rift here: http://www.ifixit.com/Teardown/Oculus+Rift+Teardown/13682 and can't figure out what the 20 pin tan colored connectors are. Does anyone happen to know what they are? (see images in link)

I think I can just build a new cable to replace the default short cable. We need to use the HMD in a larger space and can't drag around the heavy cables.

Can't you just get longer USB/HDMI cables and put the control box in a fanny-pack?

Yeah I'm pretty sure you don't want to be playing around with the cable linking the control box to the screen, its probably already at its maximum length.

HDMI 1.2 cables can go up to 10m easily without amps or repeaters, you just need to make sure the cable is up to spec and compliance tested.

Glue a belt clip onto the back of the control box, and away you go.


Edit: Just had a thought while looking at my old hacked together original xbox USB controller/cable, these things had a low strain disconnecting plug and socket mid cable near the console side. This design would make sense for trailing VR cables. Would also make it easier to consolidate the cables into one going to control box and have a breakout tail on the other side.

Has anyone tried splicing and extending the cable from the control box to the display? This would be a cleaner extension (one cord instead of 3). I don't imagine that this would break anything, but I was hoping someone would have already tried it so I don't have to be in untested waters.

How many people have actually tried extending the HDMI cable and how long a cable were you able to use? The longest example I've come across was Rift Wire Tangling Solution where a 9' cable was used.

I've tried using a 5 metre long cable, but I get a 'No Signal' on the rift. I've also tried a combination of short cables with a HDMI extender, but still no luck. The longest cable that worked (that we current have) was only 2 metres.

Has anyone gone longer than 9'?