Quick update. Just found a picture and some information of the author's monitor..
The Daewoo CMC-1418AD is also known as "CRYSTAL 14S" (made '94) and has a 14" screen.
Judging by the looks, it could be one of these little monochrome cashier monitors..

Source: *Link*

If that's the case, it's no wonder the schematic works with video on pin2 only.
Anyway, I'm not sure. Some schematics mention RGB inputs, also. What do you think ?
Could that adapter also work with normal VGA monitors or do I have to wire each RGB pin with a resistor for video/intensity ? 😕

Can't be certain about *any* VGA monitor, but if you only send an image on green and have red and blue at ground, the worst that would normally happen is a green mono picture (assuming the monitor can make sense of the sync timing). SoG isn't relevant here as you have two discrete sync lines. You could just as easily connect to red or blue for - er - red or blue mono picture.

Thank you very much, dionb! 😀
So chances aren't that bad that the DB-9->DB15 adapter might work.
I'll write back as soon as the 25MHz oscillating crystals do arrive.

Update. Sorry for the delay. The 25MHz parts arrived. I'll do a test tomorrow, maybe.

Edit: Pictures added.

Update. Just soldered the 25MHz crystals on the Winbond card..
...and got a success! 😁 It really works. H-Sync 28,3KHz, 76,4 Hz refresh rate.

My Medion CRT seems to handle it without any problems so far!
No glitches in text mode, so far. ^^

Edit: Quick video available at https://youtu.be/bnW8N6TeiPU

Wow, it does indeed work!

Colour in photographs is always tricky. I would expect it to be green mono, but some screens detect mono and output white instead. These could be either, what is it like iRL?

Awesome result! Back in the day I would never have thought this is possible! Really great! What happens when you hook it up to an LCD with VGA input? My Philips LED LCD screen so far works with any VGA resolution I can throw at it.

And you know there's an active Hercules/CGA/MDA/EGA to VGA converter? https://sites.google.com/site/tandycocoloco/m … -cga-ega-to-vga
But still, a really great idea!

Update. Did a few more tests. The other graphics card failed to display a picture @25MHz.
On neither my CRT, nor my NEC LCD, I was able to see anything.
Here's the CRT out of range message again..
- funnily, the frequencies are the same as provided by the Winbond card..

dionb wrote:

Wow, it does indeed work!

Colour in photographs is always tricky. I would expect it to be green mono,
but some screens detect mono and output white instead. These could be either, what is it like iRL?

I wasn't sure if would work or how it would look, either. I'm glad VGA can indeed work with a single RGB channel.
Thanks for the tip, again! 😁 In real life, the greens look a bit more vivid.

root42 wrote:

Awesome result! Back in the day I would never have thought this is possible! Really great!
What happens when you hook it up to an LCD with VGA input? My Philips LED LCD screen so far works with any VGA resolution I can throw at it.

Thanks! ^^ I had my doubts, if it would work with my monitors at all. If I hook my NEC MultiSync LCD 1550ME,
I sadfly get an out of range warning.. Also, graphics mode didn't work so far. Perhaps the software expects 50Hz sync, not sure.
Anyway, it works just fine for text adventures, Tetris and so on. Since my PC/XT clone has CGA on-board, this is not THAT bad.
For other people with a dual graphics setup or some ancient machinery, this Hercules (or rather MDA) "hack" is good to know.
https://youtu.be/j1N_sP8MshY

Kubik wrote:

And you know there's an active Hercules/CGA/MDA/EGA to VGA converter?
https://sites.google.com/site/tandycocoloco/m … -cga-ega-to-vga
But still, a really great idea!

Hi! Thanks for your reply! I'm not sure if you were writing to me or root42, but as far as I'm is concerned, yes I do. 😀
However not for very long (just since about two weeks or so), also I don't know how to construct that device. 😅
Say, does an universal chip programmer like the TL866/G540 would wo or does the project require an FGA progamming device ?

The FPGA can be programmed by cheap (2 EUR) programming device. Anyway, nice hack 😀 I probably wouldn't want to mod my Hercules card as I prefer to keep it intact (to preserve its historical value), but I was always wondering if Hercules can be attached to VGA 😀

Thanks! The credits go to Peter, who described this mod on his website. It was fun, though, redoing what he did. 😁
The modification can be undone easily, by the way. It's just a crystal swap. 😉
In theory, someone could use a tiny relay with two crystals wired to it (+ a diode across the relay's power pins).
So the frequencies could be changed by the simple flip of a switch.

Anyway, I have a look into the converter, too. It looks interesting.
Maybe it could even be be used with a cheap VGA->CVBS converter.
That way, I could use my old green monitor for both Composite-CGA and Hercules. ^^

Thank you @Jo22 for this thread!

It motivated me to overclock Hercules again.
Back then I tried various cards for use with Eizo 4051 (30+kHz MDA compatible monitor), but many were not cooperative, and I liked the Tamarack for working fine.
Although I had to force-feed it with an external oscillator.

For the VGA adapter there was more to do.
I put some TTL between the Tamarack chip and the output.
Three terminations each 75 ohms, umm, thats a load I do not want to have unbuffered.
The open-collector outputs then RGB-adjustable to get the desired color (green, amber, whatever).

Then some pinout change to not damage TTL monitors on the DB9 output, and a properly shielded 9-15 adapter cable to plug a monitors' input cable into.

That works fine, without any noise. Though I made a mistake and dimensioned the resistors for max output level 0.7V, I should have done 1V...

What retro activity did you get up to today?

Yeah TTL VRS Analog voltage needs to be accounted for

Personally I would hook up the Hercules (2 bits) each to their own color channel

Wire up green and red and you should get a nice amber in there.

Also ram speed is probably important when overclocking, installing faster memory may help things

Good Luck

rmay635703 wrote:

Yeah TTL VRS Analog voltage needs to be accounted for

When using open collector drivers, the minimum output voltage is about 0.1V, sufficient for a good black.
Basically the mistake is that I put a too-big pullup resistor in series with the potentiometers, so maximum output level does not exceed 0.7V.

rmay635703 wrote:

Personally I would hook up the Hercules (2 bits) each to their own color channel

Wire up green and red and you should get a nice amber in there.

Good idea! This way one could see intense as different color 😀

rmay635703 wrote:

Also ram speed is probably important when overclocking, installing faster memory may help things

Yes, but I was lucky, the card already had 100ns RAMs. I remember back then that 120 or 150ns RAMs occasionally showed the typical picture of video buffer ram errors. But often these errors are caused by insufficient stabilizer caps, so adding ceramics and replacing the tantalums often solves this problem. I did that in the course of modding the card, replacing all caps with a notch bigger ones, and placing caps where none were present, and so I do not know whether the card would have worked at all with the original "capping"...

Another thing still unfinished is that, to implement an "inverse" switch, as the Eizo 4051 had, I need to make some monoflop contraptions to have the video signal blanked while retrace. However, as I didn't get the timing right using 555 (should probably use 74121 or 123), I for now use the card without inverse.

You're welcome and thanks for the replies everyone! 😀
I'm glad that this experiment was helpful to you (and please continue with the feedback)!

retardware wrote:

What retro activity did you get up to today?

Thanks for the picture link, looks well made to me! 😀

Hercules on TFT:

- Image too big for 1550m
- Image not stable on 51vm/71vm
a) every now and then the image goes black and comes again
b) hercules textmode and gfx-mode are not "synced" they are slightly different. So image is sharp on one or the other)
c) cga-emulaton on hercules on TFT does n ot work (don't know why)
- Image is sharp on 1970vx but same problems (a/b/c)

Btw: CGA in perfect (High/Low) on the TFT's above.

Doc

Doc

Thank you for testing! 😃👍

Yeah, MDA/HGC is a bit tricky.
TFTs don't expect timings of 50 Hz and 18,4 KHz..

I assume, the reason why they sometimes do, at all, might be due to Mono TTL signals being close to PAL or TV timings (50Hz and ~15KHz).

Many TFT/LCD panels might also have been intended for installation in flat screen TVs,
so they might have been designed more tolerant.

Likewise, CGA is also related to the TV standard, albeit the American.
The timings are very close to NTSC (60 Hz, ~15 KHz).

Isn't that funny? 😆
Hercules/MDA equals PAL TV (50 Hz, higher resolution; 720 by something),
while CGA equals NTSC TV (60 Hz, lower resolution; 640 by something).
- Okay, that enough philosophising for now. 😅

Is CGA compatible with a monochrome monitor?

Edit: The timings in this thread are way off,
of course and not even close to the usual ones.
That's why I'm so positively surprised that hacks like this work.

Hi there! This might be also interesting for some of you with a VGA monitor/LCD monitor.
I heard of it a while ago already, but just remembered it while playing with an old astronomy program, MoonCalc, in Hercules mode.
https://github.com/schlae/graphics-gremlin

Of course, an old ISA SVGA card in Hercules emulation mode is an option, too. :)
Unless you need a CGA/HGC dual-monitor configuration or use an UMB card, perhaps.
Then, a real HGC/CGA card or a re-implementation like the Graphics Gremlin might be more compatible.

PS: Also interesting, but not for beginners: Hacking a classic VBS video monitor to accept TTL signals at ~18 KHz.
http://boginjr.com/electronics/rad/rgbi/ and http://boginjr.com/electronics/old/tesla-pmd60/

You've got me wondering what happens if you stick one of those 14.375ish Mhz crystals in there, whether it synchs on a TV or video monitor. Then maybe it has overscan?? IDK

My head is also going toward the simpler Amiga scandoubler plans and the stuff Grant Searle has done for composite display, using atmels, where maybe it could intercept the signal digitally then videofy it.