VGA to 3-pin VESA Stereo Adapter

Interfacing LCD shutter glasses to a standard VGA connector

This is a very simple design for an adapter that can drive professional 3D shutter glasses, and other stereo devices, from a standard VGA connector. It is able to drive most equipment that uses the 3-pin VESA DIN stereo connector, and brings stereo support to video cards that do not have the appropriate connectors already built in. However, it is not designed to directly drive the 'dumb' type LCD glasses that do not have a 3-pin VESA connector.

Although this device provides the hardware support you will still need video drivers that support page-flipped (quad-buffer) stereo. For example, most nVidia GeForce graphics cards can be patched to support OpenGL stereo, using the very nifty SoftQuadro or RivaTuner. If you want the latest version, you might find this Russian Site useful. I should warn you that patching your drivers involves some risk, so you would be well advised to back up your files first, and to do a bit of background research.

Fig.1. shows the general size and appearance of the box, although it could probably be made smaller than this. The switch on the front face of the box is used to switch the left/right eye views to give the correct stereo effect. There is a USB port that supplies the unit with power (saves using a separate power supply), and of course the 3-pin miniature DIN connector for the shutter glasses. Also visible is the VGA pass-through connector (on the flying lead).

Fig.1. Interface box

The device uses the VGA pass-through (Fig.2) to pick up the vertical sync. signal from the video card. This connector sits between the video card and your monitor. I found a ready wired connector, and added a two-core cable for the GND(10) and VSYNC(14) signals.

Fig.2. VGA pass-through connector

Finally, here is the complete circuit diagram (Fig.3) for the device. As you can see, it's a very simple device with only a single IC (74LS73). This is a J-K flip-flop that is set up to toggle the state of its output line with every clock pulse from the vertical sync. signal. The switch is used to select either the inverting /Q1 or non-inverting Q1 outputs, which has the effect of switching the left/right views. Most good stereo software will allow you to switch eyes from the keyboard also.


Fig.3. Circuit Diagram (click for a larger view)

Power for the device is derived from the USB port, through a fast blow 200mA fuse. This is an abuse of USB, but very convenient since it does not require an external battery or power supply. You could equally well use an external PSU, or power the unit from the keyboard or game port.

Some stereo devices might expect a 12V supply on the 3-pin connector, in which case you will certainly need an external supply. All the devices I have access either use 5V, or do not use the power supply rail at all.

The Small Print

It doesn't know the correct left/right order, so you have to manually select it. Make sure you set the vertical refresh as high as possible. I typically work with at 100/120Hz, with resolutions of 1024x768 or 1280x1024. Some cards may put out incompatible sync. signals in certain modes (this is speculation; I've never had any problems), but it works well at the suggested refresh/resolution on the GeForce cards.

I accept no responsibility for any loss or damage that might result from your use of the information provided here. There, I've said it :)

Testing

I've successfully used this interface box to drive the following stereo glasses/emitters. This does not guarantee that you will be able to do the same if you build this box, but it worked for me!

I've only driven the box from the nVidia GeForce family of video cards so far, but I would certainly expect it to work with others, providing that the drivers can support the page-flipping.


James Ward, 13th August 2002, www.crema.co.uk