There are several pretty cool games on the Sega Master System which support the 3D glasses: Outrun 3D and Space Harrier 3D just to name a few. What’s even cooler is that these versions of the game usually also add FM sound – go Sega! Sadly for us though, you can only enjoy the wonderful 3D experience on an original Master System with the original Sega 3D Adapter Card and with wired 3.5mm active shutter glasses. What gives?!
I think it’s possible to add circuitry to a new version of FM Power Base (and/or Power Base Mini) to support 3D glasses. But not only that, while we’re at it, I think it’s better to support modern wireless active shutter glasses instead of wired glasses. Here’s the plan!
How the Master System 3D Glasses Work
The Master System 3D Glasses work in a deceptively simple manner. The 3D Adapter Card generates a high voltage (~13V) using a charge pump triggered by the XOR’ing or the #RD and #WR signals. This is actually pretty efficient engineering since in normal operating conditions the #RD and #WR toggle constantly and thus the designers were able to avoid adding an extra oscillator circuit on the 3D Adapter Board (74HC86 parts C & D already form an oscillator). Why the high voltage? Well it’s a simple matter of the LCD used in the shutter needing a high enough voltage to operate.
The 74HC249 is mapped into high RAM (0xFFF8, mirrored through to 0xFFFB), write-only on Bit 0. At each vertical interrupt (i.e. at each frame), the game software writes a toggled value into the HC259 which causes the connected 3D Glasses to switch shutters. Effectively, the frame rate is reduced from 60Hz to 30Hz. Each frame now successively toggles between the left and right fields. More on active shutter at wikipedia.
How it all works is simple phase inversion; the comparator, which ultimately drives the LCD shutter, outputs (marked C324) on pins 1 and 14 oscillate 180 degrees out of phase with each other (simple square wave). When D0 is ‘1’ it oscillates in phase with one of the outputs and when it is ‘0’ it oscillates in phase with the other output. The active shutter in the 3D glasses use this phase relationship to enable / disable the shutter in each eye.
How Modern 3D Wireless Active Shutter Glasses Work
Well, essentially they work exactly the same except that they use an Infrared signal transmitted by your projector / TV / bluray player to activate the shutter. Some more expensive glasses even use Bluetooth – what a waste of electronics for such a simple task!
How to Make it Work?
Essentially, it’s a simple matter of decoding the D0 write at 0xFFF8 and having that bit read by a small microcontroller (AVR, PIC, insert your favourite uC here!). The microcontrollers job afterwards is rather simple, just toggle a connected infrared LED accordingly. As this paper shows there are unfortunately MANY different IR protocols for active shutter glasses depending on the manufacturer. However, I think it’s quite feasible to write firmware to support at least the 5 or 6 major brands and offer some sort of selection mechanism so that the user can switch between modes to find the proper protocol which supports his/her 3D glasses.
Where to Install it?
I would love to make an FM Power Base design which includes this functionality. The board would house an infrared LED, similar to what you find on a typical TV remote control. An additional hole would need to be drilled in the FM Power Base’s cartridge shell for the LED – no problem!
Additionally, I could potentially remake a Sega Card type 3D Adapter, similar to the original, but that would support wireless 3D glasses instead of the wired kind – now that’s cool!