Scanning disk television

[yagosaga]

Before some weeks I got a scanning disk from Peter Yanczer. This weekend I have assembled a very simple scanning disk televisor with the first results, see
http://bs.cyty.com/menschen/e-etzold...anningdisc.htm
Is somebody here who experimented with mechanical television? The televisor now is without motor synchronisation. Two MPEG videos demonstrate the effects.
I can install an automatic synchronisation or a manual remote control for the motor similar to that of early scanning disk tvs. What will be a better way?

[tubesrule]

Congratulations on getting your first images on your set!

It is my understanding that all but a few original mechanical sets used some form of frame synchronization. This was usually in the form of a synchronous AC motor that would be on the same power grid as the transmitter, or a small synchronous motor (typically called a phonic coil) that brought the main AC/DC motor spinning the disk into sync. The only set I am aware of that had no synchronization mechanism was the GE Octagon.
You could use the phonic coil method to sync your disk, and this would work very well. I also believe the NBTV web site has a schematic in which an opto-interrupter is placed around a reference hole in the disk, and used to drive a feedback loop to control the DC motor. This method also works very well.

Darryl

[old_tv_nut]

Congratulations! I see that you are using the same type of disc that I bought from Peter Y. It has the synchronization holes (which show as a bright vertical line to the left of your image), and it is relatively easy to build the sync circuit and infrared sensing fork that Peter suggests. Aso, an alternative circuit can be found on my web site, www.bretl.com. I have also seen phonic wheels that work well. Which you use is up to you. Since I am more handy electronically than mechanically, I would choose the sync using the holes and optical sensor.

[yagosaga]

Thank you very much. On the NBTV web site I have found some schematics for synchronizing the disk, using the sync circuit and infrared sensing fork:
http://www.nbtv.wyenet.co.uk/beginners.htm
All parts for this I have, and I will make it in the next days. The disk is fantastic, the lines are perfectly equal. I think this is the best way for now. For synchronising the disk with the correct phase, it is suggested to close one hole of the synchronization holes.
The technology of a phonic wheel I didn't understood, I have to learn it.

[yagosaga]

Originally Posted by old_tv_nut

Congratulations! I see that you are using the same type of disc that I bought from Peter Y. It has the synchronization holes (which show as a bright vertical line to the left of your image), and it is relatively easy to build the sync circuit and infrared sensing fork that Peter suggests.

My NBTV monitor is now working. I have taken the schematics of Peter Smith, but it was necessary to change some details because I couldn't get all the parts here.
http://bs.cyty.com/menschen/e-etzold...BTVmonitor.GIF
Line sync is working very well, but frame sync does not work. I had installed a switch for the frame sync with which I interupt the sync pulse. A lot of pictures and the schematics you will find on my web page (see my first posting). I know that the problem with the frame ync depends on the sync separation. There is noise and some overdriving in the signal.
The monitor now has an "open housing", so everybody can see how it works. In the front side I will install a glas window.
For future work I wish to install a color unit. Do you have any ideas how I can record a RGB color signal together with the video signal in one audio channel on CD?
If somebody wants to get some NBTV videos, please pm me. I send it as zipped WAV files.

[old_tv_nut]

Great results! I like your home-made video file. I tried making some myself, but had some interference between the scanning frequency and the audio sampling frequency.

[andy]

...

[yagosaga]

Originally Posted by andy

Someone needs to make a color scanning disk TV using tricolor LEDs.

I want to add a color circuit, but usually no tricolor LEDs but a number of LEDs of different colors are used. Here is a full-color, LED display calculator:

http://www.hawestv.com/amplifiers/mt.../2or3color.htm

[Eric H]

Originally Posted by andy

Someone needs to make a color scanning disk TV using tricolor LEDs.

And how about High Definition? Drill about 1000 holes in the disk and away you go!
Seriously, could that work?

[rld-tv01]

1000 holes in a disk , 1000 holes in a disk, ... paint one now .. spin them around ... 1000 holes in a disk. Either the holes have to get smaller or the disk larger and you have to climb a ladder to watch. The holes are in a spiral and do not overlap. I have seen a photograph of a 6 foot disk where they cut a hole in the floor so the viewer would be at eye level. I cann't remember the number of holes in that disk. If the holes get smaller you still have a 1 inch HD 1000 X 1000 receiver? Another HD approach is to use 2 mirror drums. The Mihay Taub design had a 30 mirror drum (each mirror at a slightly increased angle) and a 2 sided mirror doubling the 30 lines to 60. Using a 3 sided 2nd drum you would triple lines to 90. There is concerns using a single drum and 1920 technology of having the mirrors flying off as drum spins faster to permit more mirrors to cross the viewer per second. It would seem that today you probably could use some plastic injection process for applying minature mirrors? Also I'm not sure if the number of mirrors approach infinity that you would have a mirrored sphere? This would seem to be true on the 2nd mirrored multiplying device? You could then use a laser as the light source. Can you imagine a rock concert with 20 foot disks broadcasting live images to the audience.

[rld-tv01]

Here is a handheld color two way televison on the cover of the May 1918, Electrical Experimenter magazine. Could this be lost scanning disk technology or maybe something found in a crashed flying saucer. I forgot there were no crashed flying saucers found yet.

[yagosaga]

Originally Posted by Eric H

And how about High Definition? Drill about 1000 holes in the disk and away you go!
Seriously, could that work?

I think this doesn't work. If you want to get a picture with 1 inch width you have to create a Nipkow disk with 27 feet diameter! This disk will be so heavy that you need a car's motor to drive it. Or if you use a 12 inch diameter disk, the picture width is .037 inch and you need a microscope to watch TV! Another problem is the loss of light. On a 32 line disk, 99.9 percent of the light will be absorbed by the disk surface. And now you can calculate how many light you need to see a visible picture on a 1000 line disk.
32 lines a a good compromiss between disk width, picture resolution and loss of light. But much more interesting for me are the experiences with the picture quality. 32 lines are not HDTV. But for a lot of video material it is good enough to recognize what happens on the screen. News broadcasts are not suitable for narrow bandwidth television. But music videos are, tv shows are suitable too. Make your own experiences. Here is an example of a NBTV video with 32 lines (1.1 MByte, I will keep it on the server for the next week):
http://bs.cyty.com/menschen/e-etzold/NBTV_Example.zip
Download it and if you have no scanning disk monitor use a sofware player (116 KByte):
http://www4.tpgi.com.au/users/gmillard/NBTVViewer.zip
The first color tv with a scanning disk was realized by John L. Baird in the 1920s. He operated with a two color system (red-orange and blue-green).
Th whole discussion asround NBTV is in its core a discussion about what is good enough for video broadcasting. For decades we thought that the only answer is to increase the number of lines on and on. But since videos were playable on a PC with minimum resolution (remember the days of Windows 3.1 and the first AVI videos as large as a postage stamp), people discovered that low definition video enjoys the watchers too. This is the re-discovering of NBTV which lead back to the times of Nipkow disks and mirror drums.

[Jonathan]

yagosaga,

I must say, this stuff is pretty damn cool, and good work. I'm so amazed by this. I'd definately start such a project but i have lots of bills, two TVs in need of restoration, and a radio in need of restoration. :P