Here is the schematic and C source (for IBM PC) for the Sega 3D glasses
that was posted on sci.virtual-worlds a while ago.  The switching circuit
seems simpler than generating a square wave with 0x55 at 4800 baud;
I'm not certain, but I think the outportb(0x3fc, 1) and outportb(0x3fc, 3)
commands in the WaitForVerticalRetrace() function alternately set and
reset the RTS line on the RS-232 port, while keeping the DTR line constant
as a power supply.  Could someone with PC techs confirm whether bit 0 is
the DTR line and bit 2 is the RTS line at port 0x3fc on a PC?

I know next to nothing about circuits, and I haven't tried to make
this one (yet), so I can't say much about it.  I just hope it works
and that it's controled by the DTR line being constantly on, and the
RTS line causing one eye's view when set and the other eye's view
when reset.  Can someone confirm this or add advice?

I'll put this on karazm.math.uh.edu for those with ftp, too.