Hacker News Reader

Comment by amluto | Hacker News Reader

Huh, I guess they are sweeping their IR transmitter around just like a visible light. I suppose one could map all the effects one intends to use onto DMX channels. I imagine that actual selection of those effects is done out of band.

View on HN

The intention is likely that the transmitter takes DMX and sends out 38kHz IR, and the whole system of searchlight and individual armbands collectively becomes a DMX lighting. The optical wireless link part is an internal implementation detail.

I think the key thing is that IR allows the bands to work regardless of where the wristbands are located in the stadium. Additionally, they're probably using the IR to multiplex since the DMX 512 standard technically only supports 512 channels (which if each device uses a channel for color and channel for intensity, is only 256 supported devices).

With the IR technology, they are not addressing the individual lights. The bands just respond when IR splashes on them. The IR "spotlight" is just transmitting a command on repeat, and the bands display that one off command. DMX is just commanding the spot to move a certain way, and transmit a certain code.

They have a RF variant where they put the bands on each seat before the show. THOSE bands are individually addressed with RF, and their position known in advance to the setup. (If you move a band to another seat you'll mess it up). They have a special device that transmits RF across the whole venue. That device probably has a DMX hookup to take commands to transition to certain pre-programmed scenes and/or animations, and commands from a USB-connected PC.

There is a video showing the RF box with DMX input (and USB), and they talk about how they can control it from a standard lighting board.

https://i.imgur.com/Di09aD2.jpeg

It sounds like each band can be a part of (at least) 2 "groups", with the example showing groups 1-18 assigned to each stadium section, and 1-9 going all the way around from the first row to the highest/back row.

It's not hard to imagine that they've mapped each of those groups to a DMX channel, with the value indicating the color, and/or flash pattern, etc. Even if you're limited to 512 distinct groups (a single DMX universe), that's a lot of granularity. With that, any lighting designer/operator can use their console of choice to do scene and sequence programming -- no special training needed.

Yea, that sounds sane. The RF transmitter gets the DMX commands to groups, which then get translated to batches of RF bands, and then they just act on that.

I wonder if the RF system has enough bandwidth to show a movie or an animation at a decent frame rate, because that would be a neat effect.

IR has arbitrarily good spatial bandwidth — instead of a conventional moving light setup, it could be done like a projector — stick a DLP chip or an LED array at the focal plane. Then you could project a movie by literally projecting the movie as IR commands :)

I doubt the DMX part is coupled that closely to the IR. No one is bit-banging their IR protocol (or even its baseband) over DMX — even if it could work, the lighting console would need extremely special support to speak the protocol.

The DMX part would be like any other light: a pair of channels controls the coordinates to which the transmitter’s gimbal aims, one channel selects a color, one channel selects a command, a channel or two set some other parameters, etc. And the electronics in the transmitter unit convert all this to actual servo commands and to the encoded IR signal. There wouldn’t be a channel to select the active vs inactive state of the IR modulator, as entertaining as that would be. (DMX has a maximum frame rate of 44Hz. Following some links, the PixMob bits are 694.44 microseconds long. RS485 is plenty fast to carry the baseband signal, but DMX isn’t.)

(It’s been awhile, but I have operated DMX-controlled moving lights. And yes, of course I’m speculating.)

Isn't that exactly what numpad0 said? You're just agreeing with them.

> I imagine that actual selection of those effects is done out of band.

This is a bit tiresome. :) Our conversation so far (paraphrasing)

You: “it is not DMX” Me: “it is DMX, here is the source” you: “i still imagine it is not”

Why is it so hard to believe that the effects are selected “in band” using DMX? You can imagine all you want all evidence points at that it is indeed just DMX.

Here is a video where they describe the system: https://youtu.be/CPqup9_I_dU?si=voLX4gAidOcOVJJ0

> guess they are sweeping their IR transmitter around just like a visible light

For very clever reasons: (from the article) Since they are projecting infrared with moveable projector they can sweep effects around the stadium, and cover the projector with cut outs to make things like hearts.

That sounds like the wrist bands will auto-off their light when they stop receiving the IR signal. That's certainly possible and very simple which translates to high reliability.

Why do you say it's "possible"? It's what they're actually doing. I think practically nobody in this thread actually watched the linked video that explains the technology.

Why educate if it so much fun to guess around?! (:

1x channel for lamp brightness (likely pinned to "on" to provide constant power). 2x channels for pan (double fine). 2x channels for tilt. 1x channel for gobo rotation. 1x channel for gobo selection. 3x channels for standard color mix (RGB) are then sent to the modulator controlling the emitter. = 10x DMX channels per fixture. +1 maybe for focus depending on the style of fixture.

I'd bet good money that these things respond to standard DMX color codes. https://astera-led.com/wp-content/uploads/DMX-Values-for-com...

Want to hack the system? Look into whether they are using wireless DMX. Probably not, but if they are you might be able to take over the individual instruments. And I mean own them because such signals are never encrypted and the lamps won't be in a position to be rewired during the show.

Reply on news.ycombinator.com