20cm cardboard 32 line NBTV Nipkow disc mechanical televisor
This project is my very first and very basic Narrow Bandwith Television (NBTV) 32 line Nipkow disc mechanical TV set using a 20cm cardboard Nipkow disc. I have been into vintage electronic TV/video/cameras for many years but only recently gotten into experimenting with early mechanical television after watching episode 24 of Amateur Logic TV (downloadable from here) where Aussie HAM radio man Peter Berrett visits Chris Long who built a fully functional synchronized 32 line NBTV camera/monitor, I thought this was really cool so I went looking for a simple to build mechanical TV and came across a site on building a simple NBTV televisor made by a UK HAM radio man Steve CQ G8CYE and seeing it was very doable with existing parts I have in my collection I decided to make me a televisor. His site no longer exists but I saved it and here's a screen cap of his page minus the videos:
And so the construction begins...
First things first, I printed out the Nipkow disc template onto cardboard paper and punched the 32 holes in it and I reinforced the middle part of the disc by gluing two pieces of plastic to it to prevent the disc from flopping while spinning. I then looked for a suitable motor and found a standard little DC motor which suited fine with the disc.
Next I constructed the motor speed control and LED driver circuits on a breadboard so I can test to see if the circuits work. I encoded some NBTV videos using Gary Millard's Video2NBTV program (downloadable from his site) and converted the WAV files to MP3 to stick on my MP3 player to output to my circuits. On testing the LED driver circuit and a couple of LEDs, the LEDs blinked to the NBTV signal which was great, I then upgraded to 4 LEDs and tested and it worked good as well. I tested the motor speed control and it worked good too. Having the disc on the motor and testing the spinning disc over the blinking LEDs I could make out some form of visual pattern on the LEDs and was happy with that so I decided it was time to solder together the circuits and put the whole televisor together. Before I get into the official construction here are some pics and video logs of the construction and testing up to this point:
Here below are the schematics for the LED driver circuit (left) and DC motor speed control circuit (right), credit for these circuits go to Steve CQ G8CYE and his above site which is where I got them circuits from.
Now it's time to officially put the televisor together. I can't remember what order I went with the construction but I'll start with the construction of the LED light bank. Cutting a section off an experimenters circuit board I soldered 6 amber LEDs to it, then I made a diffuser using smokey sticky tape stuck over a cardboard hood and I lined the inside with chrome cellophane to hopefully intensify the light.
Next I constructed the DC motor speed control circuit (left) and LED driver circuit (right) based off the above schematics and tested them out individually to make sure they worked. For power sources, the LED circuit driver I used a 9V battery and for the motor speed control a 3V-12V variable DC power supply.
As seen in the above pics I had to also find some form of frame work to mount the whole kit and kaboodle on so I just cut two pieces of timber and nailed them together and I mounted the motor with Nipkow disc and LED light bank on top of the vertical piece of wood and the circuits on the horizontal piece. And so the televisor is nearly done, here below are the rear and front views of the televisor along with a construction video log.
Now the moment of truth, will it work??? Firing up the set having the Nipkow disc spinning and the LED driver blinking while playing some NBTV videos encoded to MP3 from my MP3 player, I could see something happening on the display but no picture, it appeared that the motor was spinning too slowly so I had to use a more powerful DC motor to get faster spin. Before doing that I tried an experiment with playing audio MP3s to see what comes up on display after watching Daniel Gosson's 2 dimensional oscilloscope NBTV video and it worked in giving some interesting patterns displaying, so it's definitely working but at wrong speed. Here below are a couple of video logs showing what I described:
So now time to find a more powerful DC motor. I went through my motor collection and picked one out that looks to be more powerful and fitted the disc to it. On testing I found the TIP31 transistor on the motor speed control circuit was overheating, so added a bunch of big fat washers to the transistor and that did the trick. Also to had to replace a couple of resistors in the motor circuit for higher values to make the disc spin faster. Here below are pics of the new DC motor and the back of the televisor with it's updated look along with a video log:
Now will it work, will it work??? Cranking it up again, the motor span a lot faster but way too fast so I still didn't see a picture, I demonstrate and describe the problems in greater detail in the following two video logs:
So I had to slow the motor down and when I did, I got pictures!!!:D I was over the moon to finally see pictures on my very first homemade cardboard Nipkow disc NBTV televisor and I was cheerin!!!:D The pictures were of course very blurry due to the fact the holes in the disc are about 1.5-2mm in diameter as I punched the holes with an awl but they looked recognizable nonetheless and having the holes wider makes for a brighter picture. So my set finally displaying NBTV pictures I am ready to make some telerecordings to show how they look. Interesting that the pictures look red despite using amber LEDs. Here below is the video logs of my set in operation displaying pictures along with a bunch of screen snaps, due to difference in frame rate there is picture breakup:
Picture of the Felix The Cat doll used in USA's late 1920s experimental mechanical TV tests and also later 1930s electronic TV tests
Silhouette of a man's face used in Australian mechanical TV tests from 1929
NBC microphone radio station logo from the 1940s
NBTV 32 line test pattern
Another NBTV 32 line test pattern
Photo of my face (totally unrecognizable on my NBTV of course lol)
My own test pattern consisting of a circle and a square, comes up distorted due to imperfections in construction of this set
The famous checkerboard used in John Logie Baird's first BBC 30 line mechanical TV broadcast "The Man with the Flower in his Mouth" back in 1930
Now my mechanical TV set is making good pictures (when in sync), I feel it's time to do some telerecordings to keep a visual record of the pictures my televisor displays. So I got a camera set up pointed as close as possible to the screen to film the pictures and I record them to DVD. I chose to use my National WVP-100N saticon tube colour camera and Sony HVC-3000P trinicon tube colour camera to telerecord the pictures due to the after image persistence characteristics of old camera tubes which allows for a smoother less flickery picture without breakup. CCDs are a problem when recording pictures that are of a lower frame rate, 12.5 frames/sec being the case for NBTV as the difference in frame rate causes picture breakup with CCDs due to their instant transistion between fields without after image persistence like old tube cameras. Anyways doing the telerecordings with the National and the Sony, as expected the pictures are less flickery and without breakup but due to lower sensitivity of older tube cameras I got dim pictures so I had to brighten them up and they look grainy but recognizable. Here below is a 57 minute telerecording using the two cameras along with a video log demonstrating the setup and procedure and a couple of pics showing the setup:
Here is an attempt at telerecording with my mobile phone camera which I had Felix The Cat on display
Now I thought I'd try an experiment seeing that a NBTV can display audio as a 2D oscillograph, I wondered what a pure sine wave would look on my NBTV display so I put some sine wave MP3s on my MP3 player and played them through to the televisor and I got horizontal bars across the display which was pretty cool. Here below is a pic of one of them and a video of various sine waves played on the televisor:
Well that's pretty much it for now with my cardboard Nipkow disc NBTV televisor, not bad results for a first attempt and this televisor marked the opening for this new awesome hobby of mine! :D