Baird 240 line Operation

[peter scott]

Well, I think I can say that neither Modeline Editor nor DTD Calculator will talk to the graphics "card" in my old XP PC. I gave up with the former and then tried the latter and it requires .NET Framework and after downloading version 4.0 from Microsoft discovered that doesn't work with my XP so got version 3.0 from Old Version. I was then able to run DTD Calculator and input the 405 line modeline info.

   

..but as you can see it doesn't know the registry location in my machine.

All in all I don't think struggling with ancient PCs is the way to go here.
If you have a PCIe x16 then you shouldn't have too much difficulty adding a two port graphics card and splitter cable. Total cost less than £15.

Peter 

[Murphyv310]

Hi Peter.
I had a look at the PC in the shed and I don't think it will do. It's quite old now and only has onboard graphics. So I think I'll look out for a more modern one on gumtree or eBay.
The notebook only has a VGA output and I don't really want to mess around with my laptop, probably wouldn't do anyway. Will come back to the thread once I've something organized.

[peter scott]

I've added another page to my website detailing the 240 line generation and showing both 405 and 240 line representations of Test Card C.

(Yes, I know Test Card C wasn't around in 1936 but it gives a better comparison than earlier test cards.)

Peter

[ppppenguin]

Excellent comparison. Obviously it can't show the very obvious flicker on 240.

[peter scott]

I wish my video capture and Youtube were able to reproduce it but sadly not.

I did try to fake it. But it's not really a fair representation.
https://www.youtube.com/watch?v=xZ2EXYezE1c

Peter

[Murphyv310]

It's really hard to do Peter. I've tried many ways with no success.

[ppppenguin]

Some years ago I designed a DVI interface to for a client. The simplified explanation is it took DVI from a PC, bunged it in a framestore and put it out as PAL/NTSC video. A colleague tweaked the PC so that it recognised the EEPROM on the interface which effectively told the PC that is was connected to a monitor that ran at 50Hz. I think I simply took 720x576 out of an ordinary 800x600 VGA image.

Could have easily modified it to work at 405 or 240, especially with the software used by Peter Scott to make a VGA/DVI output run at 405/50 or 240/25.

This solution would be far too complex and costly for amateur experiment. If I've still got some of the DVI interface cards I could easily plug them into the experimental 615>405 converter I built and repogram the FPGA to make proper syncs etc. But I think I slung out the interface cards.

[peter scott]

The graphics card syncs do differ in two respects from the EMI 405 line standard and this can cause rather critical line frequency adjustment or hooking at the top of the picture in older sets that don't have flywheel sync. Sorting this is work in progress. The existing composite sync is simply generated by exclusive OR of the line and frame pulses but the resulting inverted line pulses within the frame sync are slightly delayed relative to their correct positions. There is also no half line pulse stream. The latter is not essential and a simple monostable circuit can correct the pulse positions. See Here. To use this circuit the Modelines need to be changed such that the Composite Sync box should be unticked and the +hsync references should become -hsync.

Peter

[peter scott]

I have now made a small change so that the monostables run as an injection locked oscillator to give the half line inverted pulses. The changes are that the delay of the first monostable has been halved and the output of the second monostable now also triggers the first. See here.

Peter

[peter scott]

Sorry I messed up the link. Try here.