Modeline experiments

[murphyv310]

Hi.
A couple of Questions Re Vidblaster. When displaying the test card on both the 405 line output and on screen with Vidblaster there is serious aliasing on the frequency gratings. The original source material is perfect as it is when you drag it across the screen to the second monitor. Also the X on the screen is a little annoying, no doubt as it's the trial version.
Any ideas about the aliasing would be helpful.

[Graham G3ZVT]

Click "Video" on the top menu and select
Resolution 1920*1080 (full HD). Then "Video" Frame rate 25.

[murphyv310]

Originally Posted by rambo1152

Click "Video" on the top menu and select
Resolution 1920*1080 (full HD). Then "Video" Frame rate 25.

Hi.
Yes I've selected that, as per your instructions.

[Graham G3ZVT]

Oh. That's exactly what it does if you leave that setting as default.

I'll have a play later and see if I can reproduce the issue, and get back to you Trevor.

[Graham G3ZVT]

Any joy with this Trevor?

The only thing I can find that alters the amount of aliasing is the resolution, which I found by experiment is best set at 1920 X 1080 which when I come to think about it is a widescreen mode, both my PC monitors are 4:3 (or maybe 5:4?)
In case it's relevant, my Windows screen resolution is set to the "recommended" 1280X1024.

Is it simply that your test card is too small and is being upscaled?
The one I use is in the zip file attached, it's 1458 x 1080

[murphyv310]

Hi Graham.
Yes I think that's what the problem could be, I think also there is a certain amount of compression on Vidblaster, my original test card C when dragged across to the 405 line screen looks good but less so on Vidblaster, the one you've sent is a lot better indeed on Vidblaster. I have an even higher resolution test card C on a spare HDD and I'll try that later on once I find it.
Now have a fair size library with lots of films recorded from Talking Pictures and YouTube, also DVDs converted to MP4, Dr Who, Steptoe etc, much easier than with a standards converter.

[murphyv310]

Hi.
All running very well with this.
One question though. I'm using the basic sync feed with the two resistors, the other version has a small circuit with two chips, is there any advantages using the second method?

[peter_scott]

I think some sets have rather flakey interlacing and they work better with a true 405 line sync pulse train. http://www.nostalgiatech.co.uk/240%20lines.htm

Peter

[Graham G3ZVT]

See the images in post #34 in this thread.

That circuit is the brainchild of Peter Scott.

Although the pulse timings out of the graphics card are immaculate, the waveform lacks the trains of so-called Broad Pulses in the field blanking interval of the broadcast standard signal. Peters circuit endeavours to generate them and insert them into the signal. Without this enhancement, many sets will struggle to show any interlace, although, it has to be said that with a small screen you might not even notice.

You do need an oscilloscope to set it up.

<Edit> Hi Peter!

[murphyv310]

Hi.
Thanks for that, no problem in setting it up TBH I didn't realise there were no broad pulses as I didn't have a close look at the waveform.
Will build it up but no doubt I'll not have the chips!

[peter_scott]

I confess that designing with monostables is really bad form and it's not the easiest of things to set-up but it's nice that it's minimal.
(A flakey circuit to overcome flakey telly designs.)

Peter

Hi Graham

[peter_scott]

Looking back at the circuit I concocted I noticed that the adjustment for the line sync freq/position had a stupidly large amount of range. I just checked what I actually used. Instead of the single adjustment I included a 3 position switch selecting between 2 preset adjust pots and third pot with a knob.

The actual values set on the presets were 8.3k for 405 lines 47k for 240 lines and the knob adjustment pot was 100k just for messing about.

Looking on my Sony 9-90 on 405 lines none of the settings resulted in hooking of the top of the picture but the 9-90 was quite critical to display correct interlacing. I'm happy to report that the 9-90 worked correctly on the 405 line preset that I last adjusted 4 years ago.

Peter

[murphyv310]

Hi Peter.
Oddly my 9-90 has good interlace without the modification, both hsync and vsync are minus (-) there is no hooking on a TV62, VT4 & V310 Murphy. The only thing I see is a white line at the bottom of the picture when you reduce height.

[murphyv310]

Hi.
Perhaps a silly question. When you add the graphics card is the onboard graphics then not accessible? Would plugging in the main monitor to the onboard graphics work and then leave two possible 405 line sources available at the ATI Radeon 2400 XT graphics card or am I right off track?

[peter_scott]

Originally Posted by murphyv310

When you add the graphics card is the onboard graphics then not accessible?

That's my understanding but I'm no PC guru.

Peter

[Graham G3ZVT]

What seems to happen is this.
Any two out of the three VGA ports can be active.
They become active by seeing a monitor connected at boot up.
If three monitors are present, the on board port remains inactive.

So yes, in theory we could feed two TV signals from our ATI cards but we would only have the TVs from then on, and recovery would involve a reboot.


Regarding the monostables, I just took a look at mine, and the position adjustment is a 6.8k resistor in series with a 10k pot.
The pulse width has a 1k resistor in series with a 10k pot.

Pin 15 to VCC measures 9.5k and pin 7 to VCC measures 3.55k. My timing capacitors are both 4,700pF
I use these blue multi-turn pots, they cost next to nothing. and much better than traditional presets.

[murphyv310]

Hi Graham.
I see your circuit has at least 4 multiturn pots.
Peters circuit has two. Have you modified it in some way?

[Graham G3ZVT]

It's got six.
Three simply mix the R,G & B signals into the correct proportions, you have probably used fixed resistors.
The remaining pot adjusts the sync pulse amplitude

[murphyv310]

Ah thanks Graham, that makes sense.
I've the 221 chip on order and some pots so hopefully complete the board next week. The Murphy V310 doesn't interlace and the line sync tends to tear at the top of the picture, all others are OK without the circuit, where are you getting the supply from Incidentally?

[Graham G3ZVT]

Pin 9 of the vga connector provides a convenient +5v.