GS RGB to VGA Adapter

[Tony Cianfaglione <ab616@chebucto.ns.ca>]

Hi all,

   Here is an adapter I've been working on to get vga output without a
Second Sight card.  Any techies out there want to look this over and see
if it works for you.  Build and use it at your own risk as I haven't
tested it yet.

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                       GS RGB to VGA Video Adapter

   Here is a GS RGB to VGA converter adapter based on the VGA Hack for
the Amiga which also uses analog RGB and works great.  It will allow
the use of a vga monitor on a GS.  The original VGA Hack diagram can be
found on Aminet (the big Amiga FTP site) under hardware hacks.

   The Amiga uses separate horizontal and vertical sync so I used 330 ohm 
resistors (as suggested by someone in the Atari ST newsgroup) and tied
them together to split the composite sync.  This allowed me to get a
separate H and V sync to send to the various pins on the 74LS08N chip.

GS Male to VGA Female converter                              74LS08N chip
                                                                -------
GS Male # 2 Red -----------> VGA Female # 1    |-->--->H Sync > |1  14|
GS Male # 5 Green ---------> VGA Female # 2    |-->--->H Sync > |2    |
GS Male # 9 Blue ----------> VGA Female # 3    |       V Sync < |3    |
                                               |  |--->V Sync > |4    |
GS Male # 3 Comp. Sync ----> 330 ohm res -> H->|  |--->V Sync > |5    |
 "  "   " "   "     "  ----> 330 ohm res -> V---->|    H Sync < |6    |
                                                                -------

GS Male # 1+6+13+Shell GND ----------> VGA Female # 4+5+7+8+9+11
                     _|_
                     100
                      æF
                     ---
                      |
+5v from MB -------------------------> 74LS08N pin # 14

Horizontal and vertical sync outputs from chip go to the following:

H Sync > VGA Female # 13
V Sync > VGA Female # 14

You will need to build this on a small PCB (printed circuit board) which
is obtainable, as well as the 74LS08N chip, from Radio Shack.

Note the directional arrows on the diagram above as pertaining to the
74LS08N chip.  Horizontal sync goes IN via pin #1 and 2 and are joined
together on the PCB and then exits to Vertical sync via pin #3.  Vertical
sync goes IN via pin #4 and 5 and joined together on the PCB and exits to
Horizontal sync via pin #6.

+5 volt goes from GS motherboard to pin #14 on 74LS08N chip.

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Disclaimer:

   Be warned that using this adapter is 'AT YOUR OWN RISK' as is any
after-market hack.  No guarantees or warranties implied or given with this
diagram and instructions.  Hopefully it won't blow up your GS.  The final
result will require plugging into a vga (male) cable.  The converter will
plug right into the GS.  Let us know your results.

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