Hedghog L Standards Converter

[ppppenguin]

Not possible to reprogram a standard SCRF Aurora to do colour. Not enough space in the FPGA . The colour version used a bigger chip in the same package.

[Murphyv310]

Hi
I doubt that would work with external syncs from RGB derived from the PC unless I have got this wrong.
I'm looking for a very high quality 405 line NTSC signal that is not from conversion that introduces losses.

The quote from Geordies post 30 didn't come across.

[Geordie McBoyne]

Like any analogue colour TV system, be it NTSC or PAL, without the luxury of comb filters the picture quality will be degraded to a certain extent by the presence of the colour sub-carrier in the video signal. Apart from the more prominent line structure 405 colour won't look any better or worse than any of the other analogue colour TV systems.

The BBC digital 625 to 405 converter uses the LM1596 modulator IC as the sync and blanking mixer. Metal encapsulation version of the more common MC1486.
Video bandwidth of the 405 video is no more than 3.1Mhz. Wasn't the pre-war video bandwidth 2.7Mhz? 5 : 4 aspect ratio. That was when the active video was 83uS. Became 4 : 3 in 1949/50. Later reduced to 80uS, hence the increased video bandwidth requirement.

Geordie McBoyne.

[ppppenguin]

I've not experimented with PC derived 405 myself but it's obvious that the main problem is the non-standard syncs. This may not matter too much in many applications. In principle you can lock a decent source of 405 syncs (using TTL/CMOS, FPGA/CPLD or even a PIC processor) to the syncs from a PC. A PLL (a HC4046 will do) locked to H sync from the PC. Then divide down. NTSC subcarrier is easy that way too, as David Boynes has noted.

Then you can use a MC1377 as the coder or DIY with 1496 modulator chips as done in may professional designs including my own. A TBA520(?) works well as a coder too. It was part of the original Philips decoder chipset, with a pair of balanced modulators. A Labgear test pattern generator used it.

[`FRANK.C]

Well I finally got it finished.
The final version has a 2 line interpolator, 4 X oversampling on the 405 line output. Selectable equalising pulses and aspect ratio conversion of 4:3 => 4:3, 4:3 => 5:4, 16:9 => 4:3 and 16:9 => 5:4.
A 405 line test card and a 819 line converter.
It also has a programmable multi standard modulator.
It is a very cut down version of previous Hedghogs. While not up to the same standard it still does a reasonable good job of the conversion.

Web page here with all the details.

Frank

[Jac Janssen]

Great work again Frank! Very impressive.

The FPGA seems to be readily available and cheap as well!

Jac

[ppppenguin]

A great example of what can be done with limited resources.

[`FRANK.C]

Thanks Jac and Jeffrey
It should fill the gap until something better comes along.

Frank

[Jac Janssen]

Frank,

What would be a good way to program the FPGA?
Does Lattice have a program like Quartus for Altera?
And hardware like the USB blaster for Altera?

Jac

[ppppenguin]

Lattice supply free design tools. https://www.latticesemi.com/software I used an old version of Lattice Diamond to design a CPLD some years ago. It seemed a bit clunky compared to the Xilinx software but that may have been lack of familiarity.