While going to the cinema to see our saturday night movie, Scruffy and I walked by the waiting line where employees were giving spectators their 3D glasses for Avatar (which we didn't went to see). The sight of the obviously battery-operated glasses immediately made us wonder how they could work and how we could annoy the audience by partialy controling them ourselves.

From an old visit to the Futuroscope, I remembered that they used very heavy and ugly glasses that had an infrared sensor in between the two LCD panels which made them go out of sync if it was obstructed.

Their X101 glasses are synched by infrared and go for $110 a pair.
The other model, X102 are synched by infrared or the picture itself (white flashes used by DLP projectors) and are sold for $50 more.

The major problem is that they can't be differenciated by their appearence. X6D Ltd., the legal name behind the technology, patented the same design for the two types (US #D603445).
They all have a serial number on a sticker, but I doubt it can be used to guess the model type.

To minimize the risks of getting caught, and to be able to see the possible infrared projectors, I took my old modified Canon Powershot to take pictures at the end of the movie. This explains the black and white pictures and the bad focus.

Here are the activated glasses, right before the end of the credits roll.

The XpanD infrared projectors official documentation, says this:
"It contains 280 high-power, narrow-angle (10°) IR diodes and consumes 5 watts of power.", so if they are here, we should see them easily.

First reflex after sitting my ass on an appropriate seat: look behind to see if there aren't any purple-ish light spots with my camera. There was two, right under the projector's window !

The narrow angle of the projector's LED can be confusing at first, but that's because the projectors are made to be aimed at the screen so the light can be reflected towards the audience.

No need to explain much, here we can clearly see the 7 by 40 IR LED array.

The ridiculous 5W of power consumption comes from the fact that the transmitted signal's duty cycle is very low. That means the LEDs are all blinking on and off very fast, but are on for only a very short period of time.

The dead column shows that the LEDs are certainly 40 strips of 7 wired in series.

IR Investigator is one of the only software I use on my GameBoy which isn't a useless gadget. It can take up to 20 recordings of IR signals with various selectable sample rates ranging from a few µs to hundreds of ms and save them in RAM. I used my 256Kb flash cart this time and it didn't even fail.

Thank you Ken Kaarvik, thank you Nintendo. We have all we wanted now.

It was quite fun trying to look serious while holding the thing aimed at the projector, in front of like 30 people...

The recordings reveals that the sync signal is rather simple (they say "secured"... nice marketing move...).

Avatar is known to be screened at 144 fps (3 frames for each eye * 24fps).

This gives a 6.94ms period for the 100µs pulses sent to tell the glasses to swich eyes.
Every 20 pulses, there is a 750µs pulse 150µs after the small one to tell the glasses that the left eye has to be hidden.

This allows to only use one pulse to sync 19 frames, and make sure the 20th frame is for the right eye. So if they lose sync, you'll see at most 131ms of film with the bad pictures.