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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 1st Jun 2006, 8:28 pm   #81
jim_beacon
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Default Re: PC as a standard convertor

A little more progress.....

I have taken Kats Mk2 RGB / sync combiner, and redesigned the DC coupled amp stages using video op-amps. I can now set video level, sync level and DC offset (sync tips at 0V or -300mV, or for that matter, anywhere else) independantly. I have also done a little work on the power supply, redesigning it for 9V AC input, giving regulated +5V and -5V rails, though this was purely for personal preference.

The design still uses the basic XOR sync combiner, but as this works reasonably well, I'm going to leave it for now.

The new design still needs some tweaking, but initial results are good, and it should have more than sufficient bandwidth to handle standards up to 819 lines (the op-amp I used - AD828 - is quoted as flat to 40MHz, with a gain / bandwidth product of 140MHz).

I'll bring both versions along on Sunday.

Jim.
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Old 1st Jun 2006, 8:40 pm   #82
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Default Re: PC as a standard convertor

Jim

Can you print out the schematics and bring them on Sunday? Might also be worth printing some simple explanatory stuff to put on the display. Something along the lines of "PC running Linux and mythTV" , "RGB+sync combiner" , "405 line output"

The AD828 looks like a perfectly sensible choice of video opamp, especially if you have some in your junk box. It's voltage feedback (as agaisnt current feedback) so you don't have to choose the feedback resistor to set the bandwidth. I applaud the use of ve and -ve supplies though it isn't absolutely necessary for this sort of design. I wonder if you could sneak a bit of +/-12V out of the PC to avoid a wall wart.
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Old 2nd Jun 2006, 1:44 am   #83
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Hi,

...and then for the "Mk3" I'll proably take Jim's analogue video section and add a better SPG (I do digital design much better than analogue, really!) On the Pye monitor I do see slight problems with the interlace, lines are pairing slightly rather than being evenly spaced - it was expected that soon enough I'd find something which didn't like the taste of XORed H/V sync; I'm actually pleased that the Pye monitor's fussy as I can test out better SPG circuits with it

Oh, in between doing bits of website I'm investigating the pixel clock rates on various cards. (I can't concentrate on one thing for extended periods of time, it's better I have several projects running in parallel and switch between them as the mood takes me.) So, I'm looking at how the pixel clock is calculated, what reference crystal is used on various cards, and what range of values the PLL configuration registers can take. It all seems pretty straightforward.

I can work this out from study of the C source code for the drivers (I love Open Source.) I should be able to work out exactly what specific pixel clock rates can be obtained from various cards (without having to own the card), probably by setting up a spreadsheet or hacking a quick bit of C together (probably by copying chunks of code from the driver) to do the calculations. Once we know exactly what pixel clock rates specific cards can do, we can identify which cards should work or not, and select pixel clock rates to give the best timings.

It also seems that in at least one case, the "12MHz limit" is arbitrarily hard-coded and a patch to the driver may well mean more cards can go lower than 12MHz than originally suspected.

Regards, Kat
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Old 23rd Jun 2006, 3:53 pm   #84
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Default Re: PC as a standard convertor

Hi,

I've just become aware of the "MSNTV2" box, aka "RCA RM4100". It's a US "internet TV" box which runs the WinCE operating system. Inside it's basically a PC, though; and it appears that with some BIOS reflashing and other hacking about it can be persuaded to run Linux.

There's some information here

I'm going to see if I can get hold of one and try to get it running the MythTV front-end; and of course try to get 405-line out of it. Whether I can get 405 out of it remains to be discovered; either way it could potentially make a nice diskless fanless MythTV front-end box for the living room; meaning the back-end machine with the hard drives and tuner cards can be located somewhere else, cutting down on noise in the living-room

If I get one and get it working, details are likely to appear on the forthcoming FotH website as yet another platform which could be used. In the meantime I would advise waiting until I've got one going before anyone wastes their money on one - I don't know yet what I can make one do.

Also; I've discovered there are binary releases of the MythTV front-end for OS X - I have a Powerbook here and intend to try this out later. Again, this is a front-end only; you still needs a Linux PC with hard drives and tuner cards somewhere on the LAN running the MythTV back-end. I'm going to be looking into the possibility of persuading Mac graphics hardware to output obsolete TV standards as well.

Just thought I'd let you know what I'm up to, since I've been a bit quiet recently

Regards, Kat
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Old 23rd Jun 2006, 7:52 pm   #85
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Default Re: PC as a standard convertor

Quote:
Originally Posted by Kat Manton
... the WinCE operating system.
That sounds a horribly appropriate name
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Old 25th Jun 2006, 7:14 pm   #86
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Default Re: PC as a standard convertor

A bit off topic I know, But I'd like to say how much admiration I have for Kat and the other contributors to this project. More power to your collective elbows! I've messed about with digital electronics in previous jobs, debugging mini computer microcode and hardware design, but I have to say Unix, or Linux gives me the creeps! The least intuitive operating systems designed by humans, or maybe I'm getting old! Never the less, good work
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Old 25th Jun 2006, 7:41 pm   #87
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Default Re: PC as a standard convertor

Quote:
Originally Posted by Andy Day
The least intuitive operating systems designed by humans,
Humans ?
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Old 25th Jun 2006, 10:09 pm   #88
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Default Re: PC as a standard convertor

Hi,

I know what you mean about Unix/Linux; it's taken me a while to get to where I am. For me, computers used to be fun, then Windows stopped all that; I couldn't "tinker about under the hood" as I used to with the old 8-bit micros. Then in '98 I started playing with Linux, and computers were suddenly fun again

Anyway, coming back on-topic; I've now bought an MSNTV2 unit; for the grand sum of 30 including shipping. It's still on the wrong side of the Atlantic but now I know I've got one coming I'm reading up on it a lot. It's based on the Intel 830 chipset and there's a lot of documentation available from Intel's site.

I think right now this comes under the heading of "Advanced Projects"; at least as far as a means to get 405-line pictures goes. Once the box has arrived the first stage is to get it booting Linux, next get the MythTV frontend running with the PAL composite output on a 625-line colour set - then I'll take it from there...

Something about this appeals to my sense of humour or something - an American-market Microsoft WebTV unit, running Linux, displaying UK FreeView digital TV on a 405-line set...

What can I say... it keeps me entertained

Regards, Kat
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Old 25th Jun 2006, 10:28 pm   #89
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Default Re: PC as a standard convertor

Just as another thought for small LINUX boxes, I recently acquired a DIGI-POS point of sale processor. It is a 1.7GHz Celeron, with 256MB of RAM (uses laptop type memory cards, so you could out 512MB in), on-board sound and video, 2 PCI and 1 ISA expansion slot, and runs of a 24V supply. If I can persuade it to work, I'll try it as a Myth front-end box. It is so small, it will easily go inside a Pye D18......

Cooling wise, it has two very small, quiet fans, so it has almost zero noise.

The big question is, what is the video chipset capable of?

Jim.
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Old 24th Aug 2006, 9:18 am   #90
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Default Re: PC as a standard convertor

Ok, Where are we on this now?

I have a spare PC, so would appreciate pointing in the right direction as to the latest software, and the hardware designs - Time to stop thinking, and start doing I feel!

Any comments and pointers would be appreciated - Have no experience of Linux, or programming, so probably a good guinea pig......

Cheers
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Old 24th Aug 2006, 8:49 pm   #91
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Hi Sean,

Well, the project still hasn't got a website; a certain someone has the attention-span of a goldfish when trying to write documentation and keeps going off at tangents and playing with other interesting techy things...

The basics though:
  • KnoppMyth is probably the simplest way to turn a PC into a PVR.
  • nVidia cards from GeForce 4 onwards should work - tested so far: GeForce 4 and FX5200
  • The nVidia driver provided with KnoppMyth needs replacing - the one it comes with doesn't do interlacing properly on the RGB output.

To begin with, get KnoppMyth installed and working with output displayed on the PC monitor first. Don't bother yet replacing the nVidia driver; stick with a default unmodified KnoppMyth installation. It's probably best to have a play around with it in this state. Once it's reached a point where you can play DVDs on it, watch TV, etc., then it's relatively straightforward to replace the nvidia driver and edit one configuration file and get 405-line video out.

You then need some sort of RGB combiner; my "MkII" is the only one which exists at present; it works but still doesn't work all that well. (Lousy sync signals resulting in line-pairing on my Pye monitor.) I know why; I've just not done anything about it nor started work on the MkIII which will have a PLL in it. I've also got an idea in my head for a "KISS" minimalist design; probably at most a handful of resistors and one solitary transistor.

Everything ends up taking longer than it should, though; the "being out of work" thing means lots of time; but means I often end up working on what I can afford to work on; not what I'd like to work on.

Cheers, Kat
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Old 24th Aug 2006, 8:58 pm   #92
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Default Re: PC as a standard convertor

Kat didn't mention it, but you'll need a PC with a reasonable amount of grunt to do this sort of thing. That old P75 that's been sitting in the loft for years won't be up to the job I think processor types were discussed earlier in this (long) thread.

Paul
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Old 24th Aug 2006, 9:31 pm   #93
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Ok, sounds fairly simple

The PC is a pentium 4 1.7g, and has 1 gig of memory. I have fitted the Nvidia ge force 4 card and this seems to work well under windoze.

I have just finished downloading Knoppmyth, and will set about making a CD.

Noted the problems with the driver for the video card.

Will initially install the software without a TV card - Haven't got one of those yet - will this be ok, as I am only looking at DVD at the moment....

A circuit diagram for the combiner and sync interface would be most helpful.

Cheers
Sean
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Old 25th Aug 2006, 2:11 am   #94
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Hi,

The machine sounds up to the job

It should be possible to install KnoppMyth and use it without a TV card, but I've never tried it. Most of the functionality and purpose of MythTV relies on having a tuner card. DVD playback is currently handled via the MythTV frontend running another application (xine) anyway and the MythTV backend (which handles tuner cards, recordings, programme guide etc) isn't involved, it might be an idea to install Ubuntu then install xine (which will play DVDs as well as various file formats and streamed Internet TV etc.)

The same X modeline alteration for 405-line will work on any Linux distro. (A bold statement, there; but all Linux distros providing a full GUI use The X Window System, either the XFree86 or X.Org incarnations; both use the same nVidia binary driver, and so ought to work. I've run 405-line systems with both XFree86 and X.Org)

KnoppMyth itself is 'in development', I find it pretty easy to install; but it's not as easy to install as Ubuntu is (provided it likes your hardware, you've not got a broken router, etc, etc <sigh>)

MythTV itself is also very much 'development software' - the current version is 0.19

It might prove easier to give Ubuntu a try, get DVD playback working on it with xine or VLC, then tweak it for 405-line. Maybe. I should try it myself

If you're intending to "go the whole way" with MythTV eventually (I'd recommend the Hauppauge Nova-T PCI DVB-T "FreeView" card myself, I have two of them in one machine) then KnoppMyth is arguably the way to go.

I'll dig out the schematic for the RGB/sync combiner tomorrow, turn it into a .pdf then upload it somewhere.

Regards, Kat
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Old 25th Aug 2006, 2:49 am   #95
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Hi Kat,

Ok, semi good news!

KnopMyth is running on my PC - I am bidding on a suitable card for tv purposes....

As for Xine and playing dvds.........

Things were going so well.....

I have added the command line for decss as mentioned in another thread, butr this is not having the deisred effect......

Still, it isnt meant to be easy!

Any pointers from a seasoned Linux guru?

Cheers, and am off to bed....... ****** computers........03.49 and still playing.....I must be mad!


Sean
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Old 25th Aug 2006, 10:38 am   #96
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Default Re: PC as a standard convertor

Hi,

The schematic for the "MkII" is still on my webspace, here: http://www.technogoths.demon.co.uk/405/RGB-conv-II.png

The DVD playback issue ought to be nothing more than running the installation script when logged on as root. Typing /usr/share/doc/libdvdread3/examples/install-css.sh then hitting 'Return' is all it should take. If it's not working, there may be some clue in any messages produced when the script is run.

Regards, Kat
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Old 25th Aug 2006, 10:54 am   #97
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Default Re: PC as a standard convertor

Hi Kat,

Well after some hours of fiddling, and lots of websearching I have sorted the DVD problem - the following command entered at the root is extremely helpful....

ln -s /dev/hdc /dev/dvd

Of course I had already installed the decss package.

I think with time Mr Gates may get the elbow, as installation of software just seems easier under linux!

Will look at the schematics today, and fiddle a bit more!

Cheers
Sean
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Last edited by Kat Manton; 25th Aug 2006 at 11:06 am. Reason: Put a space in a critical place
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Old 25th Aug 2006, 11:16 am   #98
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Hi,

Ah, yes... I don't recall having to do that for some reason, I suspect on my system this link was created automatically.

But indeed, having /dev/dvd linked to the device which happens to be your DVD drive helps

Glad you're getting somewhere with this

Just a thought concerning the RGB combiner, I built mine on three seperate bits of Veroboard. One bit was the RGB summing amplifier, another bit contained only the XOR gate and associated gubbins, and the last bit was the sync/video addition section.

If you do the same, then when I've got the 'new improved' sync generator worked out you should be able to replace the board with the XOR gate one with the PLL circuit. There might be minor alterations to the video/sync combiner board (some of which needs a dose of looking at once I've got a 'scope which works... transistors going in and out of saturation aren't fast...) but I think it will be possible to convert a MkII into a MkIII, or at least a "MkII and a half"

Cheers, Kat

(PS, forgive me for taking advantage of my 'special powers', but you'd missed a rather important space out of the ln -s command...)
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Old 26th Aug 2006, 5:15 pm   #99
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Hi Kat,

Yep, building mine along a similar idea - Most of the summing amp is done, will hopefully finish that tonight, and should have the whole thing ready for testing by the end of the week....

Now, must find a smaller PC case......

Cheers
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Old 19th Apr 2007, 2:43 pm   #100
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Default Re: PC as a standard convertor

Kat's work on using a PC for standards conversion reminded me of this link I discovered a while back - DVB-T transmission from a standard graphics card on a PC running Linux see http://fabrice.bellard.free.fr/dvbt/
One day , we might want to make a modulator for those old Freeview set top boxes! - Kat, is this in your area of PC expertees?
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