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From: aduncan@rhea.trl.oz.au (Allan Duncan)
Newsgroups: comp.sys.amiga.tech
Subject: Re: 2nd Monitor on Ami
Message-ID: <865@trlluna.trl.oz>
Date: 11 Dec 89 04:25:46 GMT
Sender: root@trlluna.trl.oz
Lines: 38

From article <1521@geocub.greco-prog.fr>, by anthes@geocub.greco-prog.fr (Franklin Anthes):
> OK, it looks good, but can we hook up a second monitor to it?
> This monitor needs to be able to do text (with accents) in color
> (graphics not necessary).
> 
> Now the only solution I've come up with so far (okay call it a kludge:-),
> is to stick a brideboard in to a 2000, and then add in an external
> cga interface card.
> 
> Does anyone have any better ideas? Cost is important, so no 16M
> color frame buffers need apply:-)

I have a little box I built that goes between the Amiga's DB23 and the
monitor cable that buffers and splits R G B and sync, so that I can
drive a large display projector and see the local screen at the same
time.

The R,G & B buffers are just a PNP emitter follower driving two NPN emitter
followers, one for each output.  If you keep the incoming signal lines
short (mine are about 4 inches long) then you can leave off the 75 ohm
terminations to get 2V p-p, and then put 75 ohm in series with each
output to get the correct driving impedance.  Sync is a little messier -
the later version uses 4049 (or 4050) CMOS buffers parallelled up, with
a 390 ohm series in the output as per a CBM recommendation for NEC
mutlisyncs.

Power can be found on the DB23, and it all fits (tightly) in a 4x2x1
diecast box.

If this is beyond your capability, speak to an Elec Eng type, they SHOULD
be able to whip it up in a couple of hours, or has hardware design
vanished from the civilized world? :-)


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