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Old 23rd Oct 2016, 1:14 pm   #1
rambo1152
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Join Date: May 2010
Location: Manchester, UK.
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Default Generating 405 line video using a Windows PC

I’ve started a thread in the appropriate part of the forum about the restoration of this Cossor 918

This thread is about how I generate the 405 line programmes you see displayed on it.
https://youtu.be/T2oNculjoQc

Kat Manton did some work about 10 years ago with selected nVidia graphics cards under Linux, Jim Beacon was involved with testing and demonstrating the result, the project, known as FOTH tv, certainly worked, but a decade has gone by and most enthusiasts still prefer to convert from one obsolete television standard to our even more obsolete (but well loved) standard.

Now I am not criticising the system converters such as the excellent Aurora (desperately trying not to step on anyone’s toes here), what I am saying is that having the ability to output any stored still or moving image or indeed live webcam, from a PC at 405 (or indeed any other standard) is no small thing.

Anyhow, I chanced on a comment here discussing the FOTHtv project
http://forum.radios-tv.co.uk/viewtop...t=1973&start=0

near the bottom of that page Michael Watterson says,
“Allegedly there is a Windows driver!” and a link to:
http://www.geocities.ws/podernixie/h...deline-en.html


Allegedly? I needed to know one way or the other!

I had lying around a Dell Optiplex 780 with Windows XP Pro and an empty PCI Express slot.
I also had, from another machine, a dual-head nVidia Quadro NVS 285 graphics adapter.
So I put the card in, and installed the latest XP driver from the nVidia website.

I am thinking, if this works, I can have my primary monitor on 1280x1024 or whatever I choose, and an “extended desktop” on the 405 line set!

So I made a VGA to composite converter by cutting a VGA cable in half and splicing in three resistors and a capacitor:
http://www.geocities.ws/podernixie/htpc/vga2video.gif
If your source material is in monochrome you can omit the 100R, 150R, 390R & 20R resistors. To be honest you can’t tell much difference even with colour sources, but purists will want the correct RGB matrixing.

So, with some trepidation, I pasted Kat Manton’s 405 “modeline” into the WinModelines window.


Modeline "405i50" 8.10 664 680 752 800 377 378 385 405 -hsync -vsync interlace


and connected my crude adapter output directly to the grid of the video output valve of my newly restored Cossor 916 (I have yet to build a VHF modulator)

THE SET WAS OF COURSE POWERED VIA AN ISOLATION TRANSFORMER AND THE CHASSIS EARTHED.

I selected my secondary display in WinModelines and, with a little trepidation, clicked the little arrow...

Well, knock me over with a feather, it worked immediately, after twiddling the Horizontal and Vertical holds I had the Windows desktop wallpaper 405 line High Definition (if not HD).

But it gets even better.
If you’ve watched my Youtube presentation it is clear there is something else going on,
And it’s this, Combitech VidBlasterX Trial
http://www.vidblasterx.com/ It’s a full featured TV studio and runs on my normal monitor and outputs to the secondary 405 monitor.

It must be pointed out that VidBlasterX Trial is free-trial software, not free software. The licence terms are here
http://videoblaster.com/vidblasterhe...Licensing.html

The free trial period appears to be defined by this sentence only:
“It is therefore essential to take advantage of the Trial edition (equivalent to the Studio edition with all its features fully functional) so as to ensure that VidBlaster is suitable for your particular application before purchasing.”


OK, I may well have had a little luck on my side, especially having a spare PC, and what turned out to be a suitable graphics card, but this project was easy, bordering on the trivial, and I am left wondering why something like this is not being more widely used to serve pictures to vintage TV sets, especially museum exhibits.

Work to do.
On the computer that I am typing this I have a similar dual-head card, an nVidia Quadro NVS 290.
No doubt that will work in the XP machine, but WinModelines will not work on this Windows 10 machine, nor could I make it work with Windows 7 pro 64 bit.

I need to have a VGA monitor connected to both outputs when the PC boots, in order that both ports are enabled. This is a bit inconvenient, so I need to somehow fool card that two vga monitors are connected at bootup when there is only one real monitor. I tried by connecting the DCC data and clock pins 12><12 and 15><15 together on the 15 pin VGA interfaces. It looked like it worked as two monitors were showing in the nVidia control panel, but closer examination showed that the phantom monitor was detected as DVI not VGA. I’m probably going about this the wrong way. Any ideas?


Graham.
G3ZVT
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