31 Jan
2016
31 Jan
'16
9:33 a.m.
On Fri, 15 Jan 2016, Martin.Hepperle at dlr.de wrote:
I have got a HP 9000/217 machine with a standard video
card. This card
has a monochrome composite output (resolution is as low as about
512x400, but I might replace it with a higher resolution card). A
small 9" HP monitor that I used for testing only shows me 2 or 3 bands
of the image and cannot capture the signal properly.
All I have are modern TFT monitors which usually have VGA and/or DVI
inputs, no separate R-G-B or monochrome jacks.
What is the preferred way to connect "old" composite video signals to
a modern TFT monitor without losing too much sharpness? I understand
that interpolation is an unavoidable problem.
I don't know what the preferred way is, but as long as voltage levels
are compatible (which I suppose could be tweaked with some circuitry
anyway) you might be able to track down a standard VGA monitor that does
sync on green and also has an option to switch to the greyscale mode.
That's what I've been doing with a TURBOchannel MX monochrome graphics
adapter which outputs an analogue composite 1V p-p signal (0.7V video,
0.3V sync), 1280x1024 at 72Hz, on a TNC connector (the adapter is a pile of
weirdness of its own BTW). I have wired it via a TNC to BNC adapter and
then a 5xBNC to DE-15 adapter (both off the shelf) to the green input of
the monitor (obviously 4 of the 5 BNC inputs are loose), and in monitor
configuration I chose the greyscale mode with input from the green line.
It works just fine, and obviously there's no interpolation involved as
the monitor simply applies the single signal to all the three colour
components.
It seems that with the switch to LCD panels sync on green support has
become more common than it used to be with CRT displays; I don't know if
this has to do with input circuitry commonly used with them or is it
just that I've been lucky though. If you were happy with a green rather
than white image (which would certainly add spice to the vintage look of
the system, as a green phosphor was not uncommon in the old days), then
any sync-on-green display should do.
HTH,
Maciej