40cm plywood 32 line NBTV Nipkow disc mechanical televisor
This is a 32 line 40cm plywood Nipkow disc NBTV mechanical television. After the success of my first televisor using a cardboard disc, I thought I'd step things up a bit and go for making a much bigger NBTV televisor using a disc made of plywood. To start with I resized the NBTV template to 40cm in diameter and I printed the template to 4 pieces of paper as obviously 40cm doesn't fit to one paper. I then got a big sheet of plywood and drew a 40cm diameter circle with a compass and stuck the template directly and accurately over the circle marked on the plywood. Next I drilled the 32 holes 2mm diameter into the plywood, due to the wood's thickness and that it would reduce the light output, I felt 2mm holes were necessary despite picture quality loss.
Next step is to cut the disc. I did a rough hacksaw cut then a more finer cut and then I sanded the disc down to look as accurately circular as possible. In the process the wood did chip a bit at the edges but that's no real drama.
Now it's time to get a hold of a suitable motor for the disc. Given the weight and size of the disc I needed a much more powerful motor and I so happened to have an AC fan motor from one of my busted fans I cannibalized for parts, so I decided to use that. I did a little test run with the plywood disc loosely mounted on the motor spindle (held by blu-tack) and it worked good. Here below is my first video log of my progress with this televisor along with pics:
Just realized there was one problem with the motor, the motor spins clockwise and the 32 line NBTV format requires the disc to spin anti-clockwise. So I had to use the spindle at the rear of the motor to get anti-clockwise spin, so I mounted the disc on the spindle protruding at the rear and I hacksawed the spindle at the front off.
Next I decided to make the LED light bank. I used 20 yellow LEDs arranged them in an array 5 rows of 4. I paired each two LEDs to 220 ohm resistors and neatly as possible soldered them to a piece of bakelite board. I tested them out with the MP3 player and LED driver circuit pumping them with NBTV videos to make sure they work good and they blinked nicely to the signals so they are working great.
Now it's time to make the light diffuser. The diffuser of choice was a piece of plastic bag as the milky translucent plastic diffuses the light nicely. I decided to have the diffuser positioned 5cm from the LEDs as they are well diffused at that distance. So I cut some cardboard paper at 5cm depth and made it into a hood and glued the plastic to the front and glued the hood the LED bank and that completes the light box.
Next thing on the agenda is to get the disc secured to the motor's spindle and to mount the motor onto some form of base. For a base I used a wood box that I formerly used as a baking light box for sticky videotapes which failed miserably. So I started adding some wood pieces to the box for the motor to be mounted on and for the motor I screwed on 4 transformer lamination pieces to the motor and screwed the motor to the wood mount. Next I decided to cut some wooden washers which will go over the motor's spindle and secure the disc.
Now things start to go ugly. Firstly as mentioned in the video log I had a mishap with the motor which resulted in a break in one of the coil windings, but thankfully I fixed that with a bit of solder and insulation. Now the next issue was finding a suitable nut for the spindle which I didn't have, so tried a M8 nut, it screwed on a bit but not far. Then when securing the disc over the wood washer and tighten the nut up, the wood washer split which botched things up, so wood washers are no go! So as an alternative I put some layers of heatshrink around the spindle shaft, added a threadless nut over it and washers, straighten the disc as best as possible, tighten the front nut and glue the whole thing and hope it works. It was a total pain in the arse process to get the disc straight and secured, it drove me nuts especially when the nut got threadlocked which required vice grips to undo each time! Anyhow after a lot of mucking around along and swearing and cursing I got the disc secured without too much warping and firing it up it spun not too badly.
So it's now time to set the televisor up for testing. Firstly as seen above I've decided to use a manual braking system for the disc which is simply a block of wood with towel fabric wrapped around it, and the way I brake it is I adjust the AC motor speed with my variac to a bit higher RPM than NBTV speed and brake the disc with that fabric wrapped wood, very primitive but effective. Next I had to set up the light box and the LED driver circuit. I used the LED driver circuit from my first cardboard mechanical NBTV televisor as I wanted to quickly test it, so I rigged it up with the yellow LED light box and I glued the light box onto a block of wood and taped a number of pieces of wood underneath to heighten the light box to the right height and blu-tacked it all to the base.
Ok. Upon testing, the televisor worked and I managed to get pictures on it, unfortunately I couldn't show them on my mobile phone camera though. I had to put some heavy objects on the base as the disc was a bit wonky causing the whole thing to shake and move around the place. Anyhow I was happy to see pics on the display, however there was one problem, they looked mirrored (back to front) and it turns out I put the disc on the wrong way which was not good news as I had to get it off and flip it around and put it back on and the nut is a bitch to remove even with vice grips but after some more struggle and swearing I got the disc off, flipped it over and put it back on and secured it with glue. And that fixed it and voila I have good 32 line NBTV pictures the right way around!!!:D The pictures of course are not very sharp due to the holes being 2mm wide but they still look pretty good. Now it's time to do some telerecordings, this time I decided to use my 1990s Panasonic NV-RX3 CCD camcorder as it has low light sensitivity setting which works very well and the picture breakup is not bad at all with this camera except when you pause the playback. So using the camcorder, for the dim pictures displayed on the screen the camcorder brightened them up to look very viewable, and so I made a 51 minute telerecording of the NBTV pictures displayed. The pictures came up copper in colour so I edited the colour of the video to make them look yellow like the yellow LEDs. Here below is the telerecording followed by some screen snaps:
2D oscilloscope display of an audio MP3
1930s BBC snake logo used in the early mechanical broadcasts
Victoria Bitter VB logo
Boat silhouette picture used in the early Aussie mechanical TV tests from 1929
Man's head silhouette picture used in the early Aussie mechanical TV tests from 1929
1940s NBC radio logo
Nyan Cat YouTube viral video
Windmill silhouette picture used in the early Aussie mechanical TV tests from 1929
So that wraps up my 40cm plywood disc NBTV mechanical televisor. I am very happy it works and makes pretty good pictures. The televisor of course could use some refinements as the setup is very makeshift and I borrowed parts from my previous cardboard televisor, I will someday do that and will add the construction progress to this section so stay tuned for that. For now I'll wrap this page up with that annoying YouTube viral video Nyan Cat in 32 line NBTV Nipkow style, enjoy: