Connecting (cheap) stereo glasses

and SGI workstations

M.C.D. Roos 1-2000

Roosmcd@dds.nl






Contents

This document gives descriptions and instructions on how to connect a pair of (cheap) stereo glasses to a (SGI) workstation.
 
 

Introduction

This project began when I bought an INDY. I was impressed with itís capabilities and began looking what it could do.



I saw that it could do real 3D with special glasses. The only thing was that the CrystalEyes glasses from Stereographics were a bit above my budget (See Qualixdirect for prices).

When I a visited a local PC-shop, I noticed they were selling ASUS VR 3D glasses for $30.

Now I thought it wouldnít be too hard to connect these glasses to an Indy since all these glasses work on the same principle, or at least the glasses which use a standard monitor. So I bought a pair , made a circuit and found out it is indeed very easy.
 
 

What do you need?
 
 

Stereo-sync signal

From the "Hardware Developer Handbook", online at SGI's Toolbox.

"The stereo- sync signal indicated when the system is changing between buffers used to portray images for the right eye and left eye. The signal is a TTL signal where the "high" state indicates the left eye being shown.

There are five different connectors used for the stereo-sync signal Ėa DB-15 genlock connector, the Powered Peripheral Port, a 3-pin mini-DIN, a DB-9 connector, and as part of the 13W3 connector."

Also see "man stereo". This states that "high" indicates the right eye. On my Indy high indicates right eye, so probably the man page is right. It doesnít hurt to switch the left- and right-eye. Youíll notice this immediately as the stereo wonít work properly.

There are also some pin-outs in the stereo manual page.

If you really canít find them, I can sketch them for you since I found them in PDF files.
 
 

Short 3D shutter desciption

When we see 3D, itís because our two eyes each see a slightly different view. From the differences the distance is calculated. Now on a computer screen everything is the same distance from each eye and both eyes see the same. What we need is some way to get both eyes to see a different view on the same screen.

First we need a good resolution, 1280x1024x120Hz sounds nice. Thatís 120 images per second. In the first image we display something for the right eye to look at. The second image is for the left eye and slightly different. The third is again for the right eye, the fourth for the left eye and so on. Now you could blink your eyes alternately 60 times per second, butís itís easier to use a shutter that blanks 60 times per second alternately each eye. The shutters used in these glasse are LCD (liquid crystall display).

So your computer would have to put out a signal that signals when to blank for one eye, the other eye will be just the opposite. Most SGI machines have this, some SUNís, (some) Intergraphs and also some PCís. Because the principle is the same with all LCD-shutter glasses, you can use this circuit and the ASUS 3D glasses on all systems. Youíll only have to adjust for different voltages used for power and stereo-sync. The stereo-sync can also be deduced from the monitor-SYNC signal, but thatís for later....

For more information look on Stereographics or Stereo3D
 
 
 
 

ASUS 3D glasses VR-100g

These glasses are sold for the ASUS AGP-V3800/TVR and AGP3400TNT with VR-100 upgrade kit.

The specifications on the box reads:
 
Size
50mmx30mm
Weight
75g w/o wire
Working Voltage of LC shutter
10Volts
Consumption current
10uA
Wide Viewing Angle
50 degrees
Operating Temperature
0-50 degrees C
Storage Temperature
-20~60 degrees C

 
 
WARNING
Not everyone is used to the stereo images especially when they have not had such an experience before. 
Users should avoid watching the screen for a prolonged period of time, recommended for you no longer than 30 minutes. 
Remove glasses if you feel a slight headache or if your eyes become tired.
 

 

The first time I used the glasses, I indeed had a headache. But then I just got it all working and tried it for 45 minutes. The second time I didn't notice anything.
 
 

I bought these glasses for $30 (f65,-) at Mycom, but these will probably be cheaper in America (I've seen for $15 at an online store).

You can use other sorts of 3D-glasses, just make sure that they are LCD-shutter (not polarized ones) and you need to know the maximum shutter-voltage.

I also read that SGI pushed VESA to make the 3-pin mini-DIN the new VESA standard for connecting 3D-glasses to PC's so maybe in time there will be many (cheap) glasses which can be used with SGI workstations.
 
 

My comments on the ASUS glasses:


 
 

How does the circuit work??
 
 

What we get out of the Indy is:

What we need for the glasses is two signals:

Luckily the signal for the right eye is the same as the stereo-sync signal, only then with a "high" of 10V, and the signal for the left eye is the inverse of the signal for the right eye. What needs to be done is to amplify the signal to 10V and mirror one signal for the other eye.

For adjusting the voltage to 10V an operational amplifier is used in a comparator configuration. The reference voltage is set at 1V so the output will be the supply voltage Ė 1V if the input is greater than 1V and 0V if the input is lower than 1V. Now we already have the output for one eye.

For the other eye we use the same circuit but just use the same comparator, but with the opamp input pins switched. This is called an inverting comparator and will give the same output as the other comparator, only inverted.

These two signals can be used to drive the glasses. A divider circuit is used to get the reference voltage for the comparators. When all combined we get the following circuit:

Lines connected are shown as dots! No dots = no connection. And the pin-outs on the second amplifier are different. Use 1 -> 14, 2 -> 13 and 3 - > 12. If the picture shows as a big mess, click on it. Or save to disk and open with another program.

This circuit is verified to work on an INDY (and will therefore work on all other systems with mini-din3).

You can build this circuit on a bit of experimenterís board. Just make sure nothing shorts out. As extra precaution I used shrink tube on the connectors.

The LM324 is used because that was the first one I found lying around.... You could just about use any op-amp, that doesnít matter much. Weíre only talking about 120Hz.

But if you only have a +10V power supply (Crimson) you might want to use a low-drop op-amp. The LM324 can amplify a signal to the supply voltage Ė 1V, though the glasses will work at 9V.

So with a 12V supply you will get 11V max. With 10V supply voltage this will be 9V max. This voltage drop is lower with a special low-drop op-amp, but the glasses wil work with either 9V or 11V.

The left and right eye were found experimentally.
 
 

Safety & Testing
 
 

Building this circuit should be relatively safe. But of course accidents can happen and you can blow your SGI system up. This might be a bit of a overstatement, because there probably will be fuse somewhere, but it wonít hurt to be cautious. Thatís why I used 3 100mA pico-fuses to protect my Indy. These fuses are fast and will burn through if a current of more than 100mA flows to/from the Indy. Unless you do some real weird thing, your workstation will be all-right.
 
 

Itís also advisable to check the connectors you are going to connect the circuit to, to see if you really have the right connector and the right pin on the connector. With a voltmeter you can check the 12V/10V power signal and with an oscilloscope you can check the stereo-sync (you first need to set the display for stereo-sync or else the ouput will be 0V).
 
 

If you have built the circuit, connect it to a power supply an measure how much power it draws. If itís more than 500mA youíve probably done something wrong. Even more than 100mA is much (in that case the fuses will blow).
 
 

Please mail me with any questions, mistakes, information or working circuits at roosmcd@dds.nl
 
 

Summary of SGI systems with stereo output

This list I got from the Hardware Developerís Handbook, online at SGI website, http://toolbox.sgi.com.

Chassis
Connector
DieHard VGX, VGXT
Powered Peripheral Port (PPP)
Predator Rack
Unknown
Personal Iris
DB15 (GR1.2 or GR1.5), MiniDIN (Elan)
DieHard2
PPP, 13W3
Terminator Rack/Eveready Deskside
PPP, 13W3
Indigo (except starter graphics)
Mini-DIN
Indigo2 (except Impact)
Mini-DIN
Indigo2 Impact
DB-9F
Indy
Mini-DIN
O2 (with flat panel adapter option)
Mini-DIN
Onyx
13W3 (unsure)
Octane
DB-9M
Onyx2
DB-9M

 

Both the Crimson and the Onyx have a stereo signal in the 13W3 connector. On pin 4 (HDRIVE) the stereo sync signal is present. Pin 5 (VDRIVE) is a +10V power signal for the emitter. These signal might be easy to obtain with a 13W3-5BNC cable, RGB connect to the monitor and the HSYNC and VSYNC cables will hold the stereo-sync and stereo-power signal.
 
 

On the DB-15 (this is not like the PC-monitor connector, thatís HD-15) connector the stereo-sync is on pin 10. However there doesnít seem to be a stereo-power signal so you would have to use something else to power the circuit.
 
 

With the Mini-DIN 3 connector the stereo-signal is on pin 3. Ground is pin 2 and pin 1 connects to the +12V power (0.5A). This is also the new VESA stereo.

On the DB-9F and DB-9M connectors the stereo-sync signal is on pin 1. The stereo-power signal (+12VDC, 0.5A) is on pin 8. Pin 6 and 7 are marked digital ground return.
 
 

The Powered Peripheral Port (PPP) has a stereo-sync output on pin 3. Pin 8 is a 10V, 0.5A power supply. The ground is connected to pin 7.
 
Please note that I havenít tested the circuit on all these machines, 
Only on my Indy. In theory it should work on every SGI machine 
With an stereo output, but youíll have to check things for yourself. 
Use a voltmeter to verify that the ground and power supply signals 
are actually there, on the pins mentioned here. 
Then check with a scope if you get a stereo-sync signal 
(of course, first turn stereo on). 
If you notice any faults in this document, 
please mail them to roosmcd@dds.nl.
 

Links

This is the section where I dumped (part of) my SGI bookmarks.

   Click Here
 

To do

Some projects I would like to do in the future:

This FAQ (??) was created in a short time. If you have any questions about how things work, please mail me. I just started building the circuit on breadboard with only a plan in my head and made all the documentation at a later moment when the circuit was finished. Iím sure there are still things missing, but I wonít know until YOU tell me :)

(C) Michiel Roos

roosmcd@dds.nl