TTL RGB ==> PC
julesrichardsonuk at yahoo.co.uk
Mon Nov 5 17:31:15 CST 2007
Pete Turnbull wrote:
> On 05/11/2007 12:49, Jules Richardson wrote:
>> No, I don't need a PC. I just need *something* in the US that can cope
>> with typical UK-style picture formats (typically 'home' micros in the
>> UK will be designed around PAL signals at 625 lines interlaced I
>> expect, whereas I expect US micros of the 80s were geared more toward
>> NTSC displays of 525 lines)
>> I'm not sure if VGA will cope either - I don't think a typical VGA
>> monitor will sync down to the frequencies involved (i.e. converting
>> TTL to the necessary 'analogue' RGB of VGA is the easy bit :-)
> It's a pity you didn't ask this yesterday when you were here: I could
> have shown you my workshop monitor.
Heh - oops :-) I'm thinking that taking monitors overseas with me isn't much
of a long-term solution though; they'll fail eventually and patching them up
US-side is less than ideal.
Having a gadget available that's either readily obtainable within the US or
easily buildable seems like a better long-term solution; it's just a question
of whether the slight (typical) frequency differences / screen geometries
between the two markets are going to cause a problem in finding something that
works off the shelf.
> Alexis' idea about the circuit should work too. His surmise about 1V
> pk-pk for VGA is correct
I didn't think many VGA displays would sync down to the frequencies used by
the older kit, though?
> I've used a similar circuit to do exactly
> that, and something not too distant to combine all the signals to make
> composite video (I could have shown you the ISA card for that too,
> though it only uses the ISA bus to get power). If you need to merge
> hsync and vsync, a simple XOR gate (1/4 of an LS86, for example) will do
> well, but often you can get away with just combining them, wire-or
> style, possibly with a couple of small-signal diodes.
Yep, I've done the LS86 'trick' before for combining syncs - but lots of the
old kit I have outputs composite sync, and for driving something like VGA I
expect I'll need separate syncs. Of course I suspect I can tap into them
somewhere within the circuitry of whatever system's hooked up to the display
(ISTR that splitting a composite sync signal is a bit complicated, but it's
been a while)
> Have you tried any flat-screen monitors? Some of them are designed to
> work as TV displays, and will handle horizontal rates in the 15kHz range
> as well as signals in the VGA (etc) ranges.
Hmm, I've not tried that. The 19" Hercules LCD I have might work I suppose
(and it's so awful for normal work that it's getting dumped for a good
old-fashioned CRT soon as I get my stuff across the pond anyway)
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