405-line o/p from Linux

[Kat Manton]

Originally Posted by neon indicator

Going from VGA to composite isn't hard. I made an RGB VGA - SCART adaptor with one transistor and 2 resistors in mid 1990s and programmed the Trident ISA card in DOS to do 625 lines.

My simplest version (I'm sure I posted it here) uses just a few resistors to combine R, G & B and a couple of transistors to add H and V sync. By specifying the sync polarity in the modeline, it's 'powered' from the V sync so doesn't need a PSU and it's small enough to be built inside an HD15 cover. (It's also small enough to lose; I need to build another!)

As has been mentioned elsewhere, the syncs produced with simple circuits like these are rather crude and can produce poor interlacing on some sets/monitors. I get slight line-pairing on my Pye professional monitor. I'm intending to design something which produces composite video that's a bit closer to spec.

(Feel free to start a "405-line o/p from Windows" thread if you like; it's not an OS which has any relevance to me - or this thread.)

Kat

[neon indicator]

I was only mentioning in passing

(crawls back to bed)

[Kat Manton]

Originally Posted by Kat Manton

My simplest version (I'm sure I posted it here) uses just a few resistors to combine R, G & B and a couple of transistors to add H and V sync.

No, I didn't post it

I did post this circuit (drawn in ASCII) and Darius explained what bits to add to combine all three colours.

If I can find the thing or find my notes I'll post another circuit (maybe even drawn properly!) But that and a modulator are all that's needed to connect the VGA output to a 405-line TV (with the possibility of line pairing on some sets.)

So there's little incentive to get the 'TV out' on some cards/computers working. (Jeffrey Borinsky put me off the idea in 2006; though I did look into it a little further anyway.)

Kat

[audion_1908]

I am buying a GeForce FX 5200 so I can use MythTV to output to my 405 line tv, now all I have to do is build a VGA to composite adapter and an rf modulator, and install linux and MythTV on a spare computer!
all the realy cheap GeForce FX 5200 graphics cards are agp and I cant find a motherboard with agp.

[G3JZF_John]

audion...
405 line Modulator Design:
I have come across this design:
www.earlytelevision.org/405_modulator.html.
based around a MC1374 chip. It looks a lot easier to put together than the MC1396 design - particularly on Veroboard.
I have ordered a couple of ICs and will let you know how I get on.

John

[audion_1908]

I have some P1 or 2 motherboards, I will set one up with MythTV to test my Bush tv43.
the 405 line Modulator looks good the kit comes with pcb ICs and ceramic coil forms and for $30 with shipping!

[audion_1908]

Originally Posted by G3JZF_John

audion...
405 line Modulator Design:
I have come across this design:
www.earlytelevision.org/405_modulator.html.
based around a MC1374 chip. It looks a lot easier to put together than the MC1396 design - particularly on Veroboard.
I have ordered a couple of ICs and will let you know how I get on.

John

yes the MC1374 based Modulator looks better as it comes in a kit with the pcb, two MC1374, two ceramic coil forms and costs $30 with shipping. and also I dont have to find a 45mhz and 41.5mhz crystals, I have looked and only found ine 41.5mhz crystel and it was part of a large lot of other frequences!
I would realy like to know how you get on with the Modulator, did you order the kit?
getting the coil forms and pcb take the guesswork out of it, and I have not build that much RF stuff

[G3JZF_John]

If you get the kit, I would be pleased to know how you get on.
Crystals are a problem; 15Mhz ones can be used in third ovrtone mode to give 45MHz, but I elected to use Colpitts oscillators which are stable enough for this application.
I have just ordered the bare chips which are on their way. I know it is difficult to find coil formers but a few are available from amateur radio suppliers (few and far between these days) and I have some in my spares box.
John

[unixmanuk]

I built one of the ETF modulators, and they work very well. I have mine tuned up on channel B4. You need to experiment a bit with the coils and turn spacing to get the range you need, but once done it seems quite stable, even if not crystal controlled. Steve ships them out quite quickly. You only have to add the rest of the components yourself.

I use it coupled up to my FOTH box, which uses a simple VGA/Sync combiner fed from a Pentium P4 computer and Nvidia GEForce 5200FX adapter. The operating system I use is MythBuntu, but any Linux distro could be used with MythTV added separately. Dont forget, you only really need MythTV if you intend to use a tuner/video input device, or remote media server. You can still play DVDs etc, using the built in Linux media player.

If you need a 405/625 code portion to put into the X configuration file, and a simple combiner circuit, let me know - might save some time.

It won't approach an Aurora in terms of peformance, but as a signal source for your old tellies, it's fine (for me at least!)

[unixmanuk]

Further to the above, here's a few pics to show how I do it.

The first image shows the Linux box at the bottom, and the video combiner/modulator unit on top of the scope. There is a freeview unit on top of that and a Maplin UHF modulator.

Second Picture shows Testcard C off a CD as received from that setup by my EKCO T283.

Third picture shows an off air image from the freeview box piped through the video input of the PC's capture card.

The Moire patterning that can be seen is a camera artefact, and not on the sceen.

[G3JZF_John]

405 line modulator

I have built the modulator referred to above video section only and it is working well.

The coil is a 5 1/2 turn "Toko" type green with ferrite core. Once I had the circuit wired correctly, it worked first time bang on 45 MHz.

I had the coponents handy but it would be easier to order the kit.

I fed the modulator from the video output from my Aurora but I am now looking for a simple pattern generator circuit to produce a test sgnal perhaps on another channel.

The set is a 17" Ekco T284 -refurbed but not by me- and only roughly set up. The bars are because I used the camera on automatic settimg.

[audion_1908]

Can other nVidia graphics cars (cards) with the same GPU as the nVidia GeForce 4 or GeForce FX 5200 card be used for 405 line out?

[unixmanuk]

I don't think anyone has had any other type of graphics card than the nVidia family running like this, but that doesn't necessarily mean they won't work - it's just that the research probably hasn't been done!

I was going to try a few other common graphics cards to see if they could be coerced into being programmed to do 405, but to date haven't had the time to look into it. It's a case of finding one with a suitably programmable dot clock frequency. I don't know if Kat Manton has done any more research into it recently either.

Meanwhile, an older P4 with an AGP slot is your best bet to use with the nVidia card

[audion_1908]

I have payed the $30 for the modulator kit, it will probably take a few weeks to arrive, and I now have two GeForce FX 5200 graphics cards.

[Rubberfingers]

Originally Posted by unixmanuk

I built one of the ETF modulators, and they work very well. I have mine tuned up on channel B4. You need to experiment a bit with the coils and turn spacing to get the range you need, but once done it seems quite stable, even if not crystal controlled. Steve ships them out quite quickly. You only have to add the rest of the components yourself.

I use it coupled up to my FOTH box, which uses a simple VGA/Sync combiner fed from a Pentium P4 computer and Nvidia GEForce 5200FX adapter. The operating system I use is MythBuntu, but any Linux distro could be used with MythTV added separately. Dont forget, you only really need MythTV if you intend to use a tuner/video input device, or remote media server. You can still play DVDs etc, using the built in Linux media player.

If you need a 405/625 code portion to put into the X configuration file, and a simple combiner circuit, let me know - might save some time.

It won't approach an Aurora in terms of peformance, but as a signal source for your old tellies, it's fine (for me at least!)

Which version of Mythbuntu are you using?. I'm tearing my hair out here, I have 11.04, with an Nvidia Geforce 4 MX4000 graphics card, and the NVidia 96.43 drivers, X version 1.10.1, and the modeline I put into /etc/X11/xorg.conf seems to be being ignored.

[unixmanuk]

Hi,

To answer the question, I use MythBuntu 11.10, but I suspect your version will work ok. The graphics card should work if its a GeForce 4 family GPU.

Without knowing what you've put into the xorg.conf file, it's difficult to suggest a solution but here's how I approach the overall setup.

1) Use the proprietary nvidia drivers, not the open source ones, which won't work. I think you've got the right one anyway.

2) Build the simple VGA and sync combiner using a single transistor, 3 resistors and a capacitor. You can worry about building something more complex later. In practice, I find it works just fine. I can supply the circuit diagram, or you may find it elsewhere on this forum in earlier threads by Kat Manton, who came up with this idea originally.

3) Connect the above to an oscilloscope. This is by far the best way of confirming your video timings are correct.

4) Do your experiments by using an ssh command line session from a pc to the Linux box over a network connection. If you try to switch the X server to 405 lines while the VGA connection is still attached to a hi-res monitor, it'll flash for a split second, and switch back to the original resolution. This is because the graphics card is detecting the monitor you have connected. Use something like "Teraterm" on another PC, while your Linux box is connected to the scope via the combiner.

Alternatively, make your xorg changes and at the point of restarting the X server, disconnect the display and connect your combiner/scope.

You should see the composite output on the scope. If the switch to 405 lines works, the sync to sync time should be around 98uS. If it is, you're home and dry.

I can make the contents of my xorg.conf available for you to try, if you like. I have both 405 and 625 variations built into mine. There may be a reference issue in yours, which is maybe why it doesn't seem to work.

[Rubberfingers]

Originally Posted by unixmanuk

Hi,

To answer the question, I use MythBuntu 11.10, but I suspect your version will work ok. The graphics card should work if its a GeForce 4 family GPU.

Without knowing what you've put into the xorg.conf file, it's difficult to suggest a solution but here's how I approach the overall setup.

1) Use the proprietary nvidia drivers, not the open source ones, which won't work. I think you've got the right one anyway.

2) Build the simple VGA and sync combiner using a single transistor, 3 resistors and a capacitor. You can worry about building something more complex later. In practice, I find it works just fine. I can supply the circuit diagram, or you may find it elsewhere on this forum in earlier threads by Kat Manton, who came up with this idea originally.

3) Connect the above to an oscilloscope. This is by far the best way of confirming your video timings are correct.

4) Do your experiments by using an ssh command line session from a pc to the Linux box over a network connection. If you try to switch the X server to 405 lines while the VGA connection is still attached to a hi-res monitor, it'll flash for a split second, and switch back to the original resolution. This is because the graphics card is detecting the monitor you have connected. Use something like "Teraterm" on another PC, while your Linux box is connected to the scope via the combiner.

Alternatively, make your xorg changes and at the point of restarting the X server, disconnect the display and connect your combiner/scope.

You should see the composite output on the scope. If the switch to 405 lines works, the sync to sync time should be around 98uS. If it is, you're home and dry.

I can make the contents of my xorg.conf available for you to try, if you like. I have both 405 and 625 variations built into mine. There may be a reference issue in yours, which is maybe why it doesn't seem to work.

Thanks very much for your reply, I've just got it working, by tweaking my xorg.conf file (in the end I'm not too sure what was wrong with it). I'm using the single transistor sync combiner from the Foth site at the moment, but this further work as the field sync on my Sony 9-90 is quite critical - I will probably try the "XOR line and field sync" version.

[unixmanuk]

That's good news indeed. I too have a Sony 9-90 which is how I first proved it was working. At the time, I didn't have a VHF modulator, so I used a UHF modulator, and did the old two button trick to make it do 405 on UHF.

I since built the ETF band 1 modulator, as referred to further up this thread, which works quite well. There are many other variations that have been published over the years.

Sync can be a bit critical at times - some sets cope with it better than others. Ultimately, I'd think a separate sync source combined with the video from the computer would be better. Still, it's good fun, and is good for playing CDs, and watching off air programmes via the digital tuner. I use a USB stick with MythTv, which works well.

Look forward to seeing some pictures..