Introduction and questions about mechanical TV/NBTV software

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Introduction and questions about mechanical TV/NBTV software

Postby KLTeenkringer » Sun Oct 20, 2013 12:43 am

Best fellow NBTV enthousiasts,

I am new here, so I'll first shorlty introduce myself: I'm Thomas, live in small Belgium, am 24 years old and I have been interested in Mechanical TV ever since I read a child-book-biography about John Logie Baird at the age of 9. I attempted at that age to build a mechanical TV system, wich, in the pre-internet age, obviously failed. Now about 15 years later I friend of those days started talking about the experiments and my old fascination has caught on again, I've been experimenting for about a week now.

So far I have build 3 Nipkow disk receivers, the first disk I calculated wrong :-P, the second one was only 18cm and the ratio width-length was not good, but now attempt 3 is the more serious and succesfull one. The Nipkow disk is cut from plastic clad cardboard, better lined out, and blackened with Graphite paint. I use by now a single transistor driving 3 9000mCd LED's (white) in a cardboard box, wich gives plenty of contrast so far. The engine is now (after two days of fighting with synchronisation got quite tiring) being driven by a Pulse Width Modulator print wich gives quite some stability for the price (16 Euro kit) and simplicity of it (it is a kit produced/sold here in Belgium, don't know if it's available in other European Countrys, will have to look that up, all the parts are there, ideal for us it appears :-) ) and it appears the IC has a connection marked "Synch" (not used on the print) so I guess adding synchronisation later might be possible. I am still going to add a small modification tonight so RPM adjustement becomes A LOT finer.

And now that I got the hang of it: This stuff is FUN! Nothing beats the experimental kick you get out of this, I get pure euphoria when you get the picture stable!

But now on to the problems and questions:
-I am using Linux, and have no Windows back-up system and I wanted to create some extra files to play off, like some old movies of the day. I'm not good at programming and so on, I ended up using Linux by chance, because there was no alternative at that time. But when using Wine (Linux users will know it) the program crashes or fails to convert the files. Does anybody know any Video To NBTV program that will work readely on Ubuntu?
-The picture of the TV appears to be moving from left to right all the time, it appears a problem with horizontal synchronisation, how does that come?

Thank you very much in advance,
ow yes, I'm glad I found this hobby :-)
Greetings,
Thomas
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Postby DrZarkov » Sun Oct 20, 2013 5:55 pm

Hello Thomas,
try the "NBSC" software: http://www.authorityfile.co.uk/NBSC/dow ... fault.aspx

There is a quite good working Java version, which also works under Linux. It produces NTSC-colour NBTV signals, which are compatible with black and white NBTV.
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Postby Laurens » Mon Oct 21, 2013 12:50 am

Hi!

You can probably use the PWM motor control together with a PLL circuit. You can find a description of that circuit in the NBTV handbook.

i've already sent you an e-mail with a simple electromechanical synchronisation concept. For the other people, i'll describe it below:

Use the line sync pulses to drive a electromagnet. Put a strip of copper on the disk, near the edge, to use as an eddy current brake.
The frame starts at the missing pulse. In the ideal situation (synchronized), the disk will not be slowed down by the eddy current brake. However, when pulses are present (try to form those into a continuous current) the disk will be slowed down, and hopefully find the sync point - and stay there because it's the position that costs the smallest amount of power.
It's probably necessary to adjust size and position of the strip to get the best sync performance.
The disk should be almost synchronized, running ever so slightly too fast for this system to work.

A more powerful alternative would be mounting a rod to the motor shaft, with a magnet on the rod. The magnet should be 'held in place' while the pulses are present, and released at the missing sync pulse.
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Postby Klaas Robers » Mon Oct 21, 2013 7:03 am

Thomas,

search at the web for "MUTR" and "televisor". Then you arrive at the site of Mindsetsonline, earlier called MUTR. This is a service of the Middlesex University of Technology Resources. They sell all kind of interesting stuff, and also a small Nipkow Disc televisor.

Don't buy that thing, not that it is not working, it is working perfectly, but I think that you should continue your experiments. That is much more encouraging and you learn much more of it than buying a kit. Everybody can buy a kit.

However, on that same page there is a download of the contents of a CD with NBTV signals. You can download it, unzip it and "burn" the files that you get onto a CD-R disc. The Zip-file will give you 16 .wav-files for 16 CD-tracks. It is a really big file, it takes many minutes to load it down.

Make an AUDIO CD of the .wav files, not a CD-ROM. Burn the audio CD in "Disc at once" and without pauses in between the tracks. This will provide you with half an hour of uninterrupted NBTV video, the type you described. Use a CD-player (or DVD-player) to play the CD. The video signal is on the left CD channel output, the audio (lipsync sound) on the right CD channel output.

You can download the contents as well in inverted video. The upright video and the inverted video will fit on the same CD-R. Then afterwards you may choose to run the 1-16 tracks for the upright polarity or the 17-32 tracks for the inverted polarity. That depends on your CD-player and on your LED-driver circuit.

Heel veel succes en veel plezier.!!
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Postby KLTeenkringer » Tue Oct 22, 2013 11:26 pm

@Dr. Zarkov: Yes thank you, I will try it out later today or tomorrow. I'll let know how it functions.

@Laurens: Yes sounds like a great idea. I have been thinking about some synchronisation schemes too, but your idea holds a good concept. Looks a bit like the old Phonic Wheel method. Altough a copper-strip might be easier to mount. And as your latest test showed aluminium works too, as long as drive power of the motor is not to high, if you could post the link to your Youtube film with the tape-recorder showing it? I haven't saved it.

@Klaas Robers: I allready had downloaded the NBTV files of the MUTR Televisor site, they work perfectly. Laurens has provided me with some additional converted files to view. I have no extra CD-player however, I run the line-out of my laptop, it works quite OK, picture is becoming a lot better than expected, I will try to fix this soon, or maybe even record them to tape. But then I need a good tape-recorder too, might have a look at some second hand ones.
Ow and no panic: I will continue experimenting, I've been experimenting with electronics for as far as I can remember, mostly tube-based, and it's a thousand times more fun (albeit frustrating sometimes) than buying anything. The ultimate point is to build a Televisor set using tubes, what I'm doing now is only proof of concept of some ideas. If I buy the Televisor Kit it would be to convert it to camera use, since when your camera takes a wild run, it would be impossibe to synch the receiver. Altough I have come to the conclusion that the Receiver was the easy part so far. A camera will demand low-noise pre-amplifiers, sensitive light-detectors and so on but I'm used to building Radio Circuits up to the UHF-band so the electronic part shouldn't be a problem. The main problem right now is sourcing the mechanical parts, I'm demolishing household electric apparatus at an alarming rate :-). I'm going to source a motor with a long axle so I can put nuts and other mechanical parts on it for an attempt at electromagnetical synchronisation. We'll see how it works.
Owja, bedankt, jij ook succes! :-)
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Postby Klaas Robers » Wed Oct 23, 2013 1:16 am

Thomas,

In the past many experiments have been done to record NBTV video onto cassette and/or magnetic tape. That is extremely difficult as the frequency bandbreedte should be flat (3dB) from 2 Hz to 10 kHz. But even more difficult is the phase response of the recording process. Before you try NBTV try to record a square wave of say 100 Hz on your tape recorder and watch the wave form of the played back signal. No square wave at all. This is because of the HF biassed recording process.

CD does not have that problem. The wave form is kept as it is, from 2 Hz to 20 kHz. It looks as if CD (Recordable) is developed for NBTV video. If you don't have a CD player or DVD-player, buy one, second hand, especially for this purpose. See that it has a line output (tulp plugjes). Record the CD-R disc in your computer and you have a perfect source of NBTV video. Baird has been dreaming of this.

The clubshop of the NBTVA (www.nbtv.org) has more CDs with video and sound, very recently also in colour.
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Postby KLTeenkringer » Sun Oct 27, 2013 9:44 pm

Beste Klaas,

Ok, sorry to hear that. Right now I use the line out output of my laptop, with quite some succes. Haven't changed anything so far, I have been dragging the thing around to anyone who is interested in a demonstration, to great amusement of some people. My best friend called it "the funnest TV she'd ever seen" and wants one too, so that will be the first task at hand, making another simple televisor. She didn't want synchronisation as she enjoyed the game of "chasing" the picture.
I have found out that with the Pulse Width Modulator you can keep the disk nearly synchronised but that is VERY sensitive to the enviroment. Talking loud while sitting in front of it causes instability! Also it needs quite some time to stabilize, I presume this is due to heating of the DC motor I have read about. But after about 20-30 minutes of operation it becomes quite manageble to keep the picture stable. The main problem being the fact that at every start of a new clip it must be re-synchronised horizontally. This requires some "running up or down" but with the 10 turn potentiometer I use this is quite easy. It just takes practice, you have to get the "feeling" of the inertia of the disk + flywheel on the motor. The fact that I see one frame up and down besides the "main picture" helps greatly in this, this is because I have no lense and the Light-Box that is too long.
All in all it is quite satisfactory and I don't feel the need to add electronic Synchronisation immediately, only make a better (more mechanically stable, with a bit smaller holes because the picture is a bit blurry) disk and mount it in a cabinet. I have tought of some analog synchronisation schemes but first I want to try something different.

Plans now are:
-Build second set with smaller disk and a lense using the same techniques, only with much more rugged construction.
-Some sort of camera. The amount of stability I have right now has made me confident enough that it should be possible to get away with no Synchronisation for simple tests. It would probably be a Flying Spot scanner since this is the simpler of the types it appears to me.
-But first: Since I live in Belgium I would like to try to pick up the NBTV signals broadcast in the UK on 80 meters band I have read about on the NBTVA site. I have sent a message to the NBTVA to ask some more information on this. I would try to do this with an upgraded version of my Regenerative Receiver, it would fit perfectly for the somewhat wider signals. And offcourse it would be a pure historic thrill :-)! I wonderded if anyone here has tried to receive these signals?

Kind Regards and have fun experimenting!
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Postby Klaas Robers » Wed Nov 06, 2013 2:59 am

Beste Thomas,
the advantage of having a Cd-player is that if you made a CD in "disc at once" with no pauzes in between the tracks, that the video signal continues from track to track without any resynchronisation needed. Especially is you use sync by hand this is important, no resynchronisation.

Also the CDs of the club have this and it took me quite some effort to ensure that there is no sync hicup from one clip to the other. However if you make a "search" to another track the sync is lost of course.

It looks as if you feed the motor with a constant CURRENT the speed is more constant than if you feed it with a constant voltage. The NBTV Handbook gives a circuit diagram for constant currend feed.

Inform yourself about the transmissions on 80 meter by sending an e-mail to Vic Brown. I once tried to receive them but I naver had success. I think the conditions on 80 are too bad for it.
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