Re: Electronic multi-switches

On Feb 24, 1:47 am, "Aly" <,shfskf...@xxxxxxxxxxxxxxxxxx> wrote:
"SixteenThirtytwo" <sixteen_thirty...@xxxxxxxxx> wrote in message

news:1172247671.828872.157290@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

I'm trying to design a video output board for my Mega STe computer

Small world init' :-) I'm doing my ST right now so have everything fresh in
my mind from only a few minutes ago. :-)

Sure is!
I didn't expect that! Cool :-)


With modern televisions and monitors you should be ok since if the sync
signal is out of range then the monitor simply shuts down.

In the olden days when almost everything was done in an analogue fashion
this clearly was a problem. But almost every signal today is processed
digitally. As long as it's not over voltage then it's not a problem.

True. I want my circuit to be as "idiot proof" as possible, meaning
that whatever combination of monitor/TV and switch setting I choose I
can't blow anything up.
The Atari colour and mono monitors can probably be regarded as "old"
and care has to be taken with the sync signals, so this is why I'm
designing it so that I'll be on the safe side.


Possibly the only change to your circuit would be to make the 150R RGB
resistors presets. Only reason I say that is that I'm finding here right
now that 150R is a bit too much, 100R seems more appropriate.

You mean for the SCART connector?
Yes, those values aren't definite, so you may very well be right. I
might even have to experiment a little.


I'm making up a low/med/high for a Samsung 19" LCD television which has a
VGA input (LE19R71BX). Literally all I have is a DPDT switch which connects
ST-pin-4 and GND, and in the other direction supplies 12v to the SCART-pin-8
function pin. It's working fine. I just flick the switch from 31.5Khz to
15.25Khz input and the Samsung does the rest. It's just like having a
multisync monitor.

That sounds like a great solution for your setup. I used to have an
NEC Multisync II which I used with my ST. Now I have an SM-144 for
mono mode however and it's a LOT better. I really use mono mode the
most, but want to make the computer setup as flexible as possible.


Maybe the other thing I've found is that an LCD doesn't quite process the
ST's 15.25Khz low/med as well as what an old Philips CM8833 *analogie
electronics* CRT does. I get what I'd describe as digital artifacts if you
know what I mean.

Probably the same sort of compromise my Multisync II gave me. The
opposite was the fact there (although I've never had a dedicated Atari/
Atari compatible colour monitor to compare with) where colour was
great but mono was fuzzy and unclear. Not good on the eyes. It was a
great relief to exchange it for an Atari SM-125 mono monitor, then
later the SM-144.


My suspicion is that these LCD televisions with VGA inputs are nothing more
than VGA monitors with a scan doubler bolted on for the television. VGA
signals seem pure and precise. Yet the 15.25Khz SCART images seem a little
bit processed.

That may be true. I don't know what I'll be ending up with myself when
it comes to display options, but most likely it'll be a VGA monitor of
some sort, connected to the VGA (mono) output. The Mega STe will be
recased (inside a 19" rack enclosure) and modified in many ways and
will be more or less a dedicated MIDI computer for music purposes.
Still, I might play the odd game now and then which is why I don't
want to restrict it just for mono mode.


Hope you liked that 16/32 :-) You came into the wild west wilderness of
Usenet and found someone doing something equally retro.

Yeah, sure did :-)
Glad to see other Atari users out there.


Hallvard

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