10 Jan
2008
10 Jan
'08
3:29 a.m.
Hi,
I recently received a Commodore A2024 monitor. This is a 15" monochrome/
grey-scale monitor which has a special converter board inside, that
converts the 15kHz video output by an Amiga computer to 31kHz. It also
supports a "tiled" mode, whereby Amiga video frames are combined to
produce a 1024x800 or 1024x1024 pixel image.
Unfortunately the monitor was damaged in transit and the tube is
cracked. However the converter board should be usable. I want to make an
adaptor to connect the converter board to a standard VGA/multi-sync
monitor.
Has anyone on the list connected an old workstation (or maybe an Atari
ST?) with monochrome output to a modern monitor? Those should be
similar.
There should be no problem with the horizontal and vertical scan rates.
I need to look at the board circuitry, but I'm pretty sure the
horizontal and vertical sync signals will be at TTL levels, which is
fine for connection to a VGA monitor.
The monochrome video signal is output on a phono/RCA socket. Inside the
monitor, a coaxial cable goes from that to the PCB at the end of the
tube.
I need to determine the video signal level. Apparently VGA uses 0.7V
p-p, so I might need to add a resistor in-line to reduce the voltage if
it's any higher. Unfortunately I don't have access to an oscilloscope.
Could I just arrange for a full-screen white image to be shown, measure
the voltage using a normal DC multimeter, and multiply up the value
shown to account for the proportion of each scanline corresponding to
sync/flyback?
Once that issue is solved, I should be able to connect the video signal
to the green signal pin of a VGA monitor and get a green picture. In
order to get a grey-scale picture, can I simply connect the video signal
via resistors to each of the R, G and B pins on the monitor connector?
If so, what resistor values would be needed? If not, I guess I could use
or build a 1-to-3 splitter/amplifier circuit, then connect the 3 outputs
of that to the R, G and B lines.
-- M
10 Jan
10 Jan
3:48 a.m.
Hi Mark,
Its very easy to make a simple cable to connect an ST to a VGA
monitor, but it only comes up in Monochrome, the key is to use a
multisync monitor.
The info is here:
http://www.atari-forum.com/wiki/index.php/Atari_ST_to_VGA_adaptor
I was messing around with some LM1881N's to hook an Atari 800 direct
from its raw RGB outputs from the motherboard to VGA
and had limited
success.
Curt
Mark wrote:
Hi,
I recently received a Commodore A2024 monitor. This is a 15" monochrome/
grey-scale monitor which has a special converter board inside, that
converts the 15kHz video output by an Amiga computer to 31kHz. It also
supports a "tiled" mode, whereby Amiga video frames are combined to
produce a 1024x800 or 1024x1024 pixel image.
Unfortunately the monitor was damaged in transit and the tube is
cracked. However the converter board should be usable. I want to make an
adaptor to connect the converter board to a standard VGA/multi-sync
monitor.
Has anyone on the list connected an old workstation (or maybe an Atari
ST?) with monochrome output to a modern monitor? Those should be
similar.
There should be no problem with the horizontal and vertical scan rates.
I need to look at the board circuitry, but I'm pretty sure the
horizontal and vertical sync signals will be at TTL levels, which is
fine for connection to a VGA monitor.
The monochrome video signal is output on a phono/RCA socket. Inside the
monitor, a coaxial cable goes from that to the PCB at the end of the
tube.
I need to determine the video signal level. Apparently VGA uses 0.7V
p-p, so I might need to add a resistor in-line to reduce the voltage if
it's any higher. Unfortunately I don't have access to an oscilloscope.
Could I just arrange for a full-screen white image to be shown, measure
the voltage using a normal DC multimeter, and multiply up the value
shown to account for the proportion of each scanline corresponding to
sync/flyback?
Once that issue is solved, I should be able to connect the video signal
to the green signal pin of a VGA monitor and get a green picture. In
order to get a grey-scale picture, can I simply connect the video signal
via resistors to each of the R, G and B pins on the monitor connector?
If so, what resistor values would be needed? If not, I guess I could use
or build a 1-to-3 splitter/amplifier circuit, then connect the 3 outputs
of that to the R, G and B lines.
-- M
5:12 a.m.
On Wednesday 09 January 2008 22:29, Mark wrote:
(Snip)
The monochrome video signal is output on a phono/RCA
socket. Inside the
monitor, a coaxial cable goes from that to the PCB at the end of the
tube.
I need to determine the video signal level. Apparently VGA uses 0.7V
p-p, so I might need to add a resistor in-line to reduce the voltage if
it's any higher.
Or more properly a voltage divider.
Unfortunately I don't have access to an
oscilloscope.
Too bad, as the peak-to-peak amplitude of the signal is really what you'd
need to know here.
Could I just arrange for a full-screen white image to
be shown, measure
the voltage using a normal DC multimeter, and multiply up the value
shown to account for the proportion of each scanline corresponding to
sync/flyback?
Not likely.
Once that issue is solved, I should be able to connect
the video signal
to the green signal pin of a VGA monitor and get a green picture. In
order to get a grey-scale picture, can I simply connect the video signal
via resistors to each of the R, G and B pins on the monitor connector?
If so, what resistor values would be needed? If not, I guess I could use
or build a 1-to-3 splitter/amplifier circuit, then connect the 3 outputs
of that to the R, G and B lines.
A VGA monitor is (in most cases) still going to be looking for sync signals on
separate pins. And you're starting out with composite video? This isn't a
project *I* would care to tackle, and I am way ahead of you when it comes to
equipment and background with this stuff.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
9:51 p.m.
I need to
determine the video signal level. Apparently VGA uses 0.7V
p-p, so I might need to add a resistor in-line to reduce the voltage if
it's any higher.
Or more properly a voltage divider. Unfortunately
I don't have access to an oscilloscope.=20
Too bad, as the peak-to-peak amplitude of the signal is really what you'=
d=20
need to know here.
Could I just arrange for a full-screen white
image to be shown, measure=
=20
the voltage using a normal DC multimeter, and
multiply up the value
shown to account for the proportion of each scanline corresponding to
sync/flyback?
Not likely. 
10:22 p.m.
New subject: 1772 floppy controller hack...
In my quest to use 1.44MB 3.5" floppy drives on my Ampro, I've found that
the 1772-02-02 variant of the floppy controller chip can be "overclocked"
to 16Mhz in order to correctly read/write 3.5" high density disks.
Beyond needing to adjust the step rate to 6ms to compensate for the
doubled clock rate, is there anything else I should be aware of? I've
seen many mentions of this particular hack on the Atar ST line of
computers to achieve the same goal, but I wasn't sure if there was some
other factor I had to be aware of.
Thanks all!
g.
--
Proud owner of F-15C 80-0007
http://www.f15sim.com - The only one of its kind.
11 Jan
11 Jan
12:51 a.m.
New subject: 1772 floppy controller hack...
which *Ampro* are you talking about, and how did you
manage the overclocking? If asked, I would have
suggested, from memory, that the LittleBoard/PC
already supported high density floppy drives, but I
could be mistaken.
--- Gene Buckle <geneb at deltasoft.com> wrote:
In my quest to use 1.44MB 3.5" floppy drives on my
Ampro, I've found that
the 1772-02-02 variant of the floppy controller chip
can be "overclocked"
to 16Mhz in order to correctly read/write 3.5" high
density disks.
Beyond needing to adjust the step rate to 6ms to
compensate for the
doubled clock rate, is there anything else I should
be aware of? I've
seen many mentions of this particular hack on the
Atar ST line of
computers to achieve the same goal, but I wasn't
sure if there was some
other factor I had to be aware of.
Thanks all!
g.
--
Proud owner of F-15C 80-0007
http://www.f15sim.com - The only one of its kind.
____________________________________________________________________________________
Never miss a thing. Make Yahoo your home page.
http://www.yahoo.com/r/hs
10:29 p.m.
IIRC someone suggested using a multisync monitor, that is likely to be the cheapest and
simplest way ahead. SyncOnGreen to Grn should give you a nice green greyscale - white
would require a video buffer (the problem is loading by the terminators - which might just
be switchable / linkable). However UK prices for 19" NEC MultiSyncs are about ?200,
i.e. double the price of cheap TFTs. Perhaps you can pick up a small second hand one.
Boxes are available to convert RGB to VGA, see e.g. http://www.cadesigns.co.uk/mi1a.htm.
Not cheap, just slightly less than a multisync monitor, but the target market is banking.
I have used these for (VaxStation) VCB02 (RGB) to (VGA) TFT conversion. Although the Hz
fit of the screen image can be a bit "iffy" - infinitely better than working on
the console port.
If you wish to roll your own, which I'm certain you don't, the Intersil EL4583
data sheet and associated apps notes are a good place to start. Additionally, the apps
notes contain a fair bit of background information which may be of interest.
Martin
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org] On Behalf
Of Tony Duell
Sent: 10 January 2008 21:52
To: cctalk at classiccmp.org
Subject: Re: Converting monochrome video signal to VGA monitor?
Most VGA monitors terminate the input siganls into 75 ohms -- basically
there's a 75 ohm resistor from the input signal to ground. You can use
that as the lower resistor of the potential divider.
The first thin to do is to see what supplies the converter board takes.
If it takes some high voltage (say around 40V), this could well be for a
video output stage on that board, which will complicate things. Look out
for any signs of a step-up voltage converter on the board too.
Assuming there's just a 5V supply, I think it's safe to assume the video
output siganl has an amplitude of less than that.
A tirck I've used in the past to find the peak value of a signal in the
absense of a suitable 'scope (in my case, the signal was a narrow pulse,
so I'd hae needed a good storage 'scope), is to use an analogue
comparator chip.
Get a suitably fat one that covers the voltage range you're looking at
and power it approriately. Connect one input to the signal under test
(the video output signal here), the othre to a mutil-turn potentiometer
conencted across a stable voltage source. Monitor the output of the
comparator with a logic proe, and turn up the pot' until the output just
stops pulsing. Now the voltage on the pot' slider is just above the peak
voalue of the signal. And since that voltage is a steady DC one, it can
be measured with a DMM.
-tony
I need to
determine the video signal level. Apparently VGA uses 0.7V
p-p, so I might need to add a resistor in-line to reduce the voltage if
it's any higher.
Or more properly a voltage divider. Unfortunately
I don't have access to an oscilloscope.=20
Too bad, as the peak-to-peak amplitude of the signal is really what you'=
d=20
need to know here.
Could I just arrange for a full-screen white
image to be shown, measure=
=20
the voltage using a normal DC multimeter, and
multiply up the value
shown to account for the proportion of each scanline corresponding to
sync/flyback?
Not likely. 
12 Jan
12 Jan
12:19 p.m.
However UK prices for 19" NEC MultiSyncs are about
?200, i.e. double the
price of cheap >TFTs. Perhaps you can pick up a small second hand one.
Martin, not all nec Multisyncs syncs down to 15 KHz, what seems to be
the case. As far as I remember, only the Nec Multisync 3D syncs down to 15
KHz.
But Samsung LCDs usually sync on 15KHz, maybe it is worth to take a
look.
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