Instructables


Recently I saw a documentary about the history of the television. And to my surprise they showed that there existed a mechanical television before the well known CRT televisions.

Those mechanical televisions or televisors were pretty smart and simple.
A CRT is simply an electron beam that scans a surface covered with a luminescent phosphor line by line. And the intensity of the beam is then directly proportional with the whiteness of that particular spot on the screen.

A televisor works in a very similar way. But instead of an electron beam, holes are used. Holes in a spirally pattern on a disk scan a small area as the disk rotates. After that particular area an electrical lamp varies its intensity. Bright means a bright spot wherever a hole is located.

There are some videos on youtube from people who have built other televisors. With more lines and far better image quality than this one. (but they aren't made out of cardboard)

This instructable documents the build of such a very small 24 line televisor completely from scrap cardboard, scavenged electronic parts a laptop and an arduino.
The image quality is very, very low but it is built out of cardboard and it has only 24 lines.
But it was a fun build.
If you want a good display, there are much better alternatives, (pretty much everything is a better alternative).

A lot of things that I did here were a first for me so I had to improvise and will have missed out on probably much more efficient solutions. So, expect some very naive approaches.
But the final result kind of works and can display something in a recognisable way. (But that's about it)
I have updated some things and mentioned what could be done better.




This is the general structure of the instructable:

Step1: Materials
Step 2-8: Building the cardboard hardware of the televisor.
Step 9: Building a led lamp.
Step 10: Making a speedometer to register the rotating speed of the disc.
Step 11: Writing a program to convert normal photo's/images to a sound file. (to modulate the lamp)
Step 12: The electronics.
Step 13: Arduino to control the speed of the disc.
Step 14: Results


Have a good read. And thank you to the people in the comments who gave a lot of good advice.

 
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Cambenora10 months ago

Excellent instrucible, Sparticles. Top marks.

Great project, and great iinstructable! voted!
Sparticles (author)  stringstretcher1 year ago
Thank you!
Snerdguy1 year ago
Nicely done. The original cameras used a photomulitplier tube. It was a vacuum tube that detected the light coming through the scanning disk and amplified the signal. The receivers could be quite difficult to sync up because they depended on the camera and receiver disk to spin at exactly the same speed. So, they required quite a bit of adjusting and were rather noisy. That technology was also used in some of the first facsimile machines except the camera disk would scan an image and the receiver would expose photo sensitive paper. It was primitive. But it worked.
Sparticles (author)  Snerdguy1 year ago
A PMT would work very well.
However, wikipedia says the first demonstration of a PMT was in 1934.
And they used mainly photoelectric sensors because they switched over to flying spot scanners (another interesting idea) because the photoelectric sensors were too weak.

Thanks for the input!
sitearm1 year ago
@Sparticles; Hi! I also read, although further back in time, a history of television. It was, to me, a time when "credit" for great inventions passed from assigning it to individuals (such as Edison - the lightbulb) to teams (such as John Bardeen and Walter Brattain - the transistor) to... well... bigger teams. I've tweeted your Instructable. Cheers! : ) Site
PS I'm still not sure all the great inventions were actually just to one person (such as Alexander Graham Bell - the telephone)
Sparticles (author)  sitearm1 year ago
Thanks!
Yes, although it wasn't always the rightful person who got the credit. Also, the challenges became larger and more difficult for one person to solve.
12much1 year ago
Not sadly!! Nice job! We expect much more from you in the future!-)
Sparticles (author)  12much1 year ago
Thanks, I will very likely do more indeed. But it will take some time.
alzie1 year ago
Way cool, very nicely done!
I can see some thing like this used
to make a cheap thermal IR camera.

Your led drive ckt could use a couple of tweaks.
1. The anode of the led needs to go to +5V
2. Take the feed back from the source of the fet.
This will produce linear led current as
opamp will be monitoring / correcting the fet current.
3. Also, make sure that your audio channel is DC coupled.
AC coupling will droop over long periods and
screw up the brightness level.
This will fix the large dark / light area problem, or
use a diode clamp DC restoration ckt
to automatically set the black level.
This has been done in analog TV during hor sync time for the same reason.
Sparticles (author)  alzie1 year ago
Thank you for the feedback!
That is a very intriguing idea.

1)Ow, I've put the LED wrong in the schematic. How didn't I see this?
And the rules say I can't modify this instructable after the deadline.
Well, for everyone who reads this: "In the Schematic in STEP 12, the LED should be
turned turned around."

2)Thanks, that didn't cross my mind. This is a much better approach.

3)Ah, that can be, I've never heard of such a clamp but diagonally reading wikipedia it looks usefull.
De nada.
I hate proofing my own stuff!
I always overlook the same mistakes over and over again.
zawy1 year ago
"As you will see, my technical skills are quite limited"....aww come on. To wit: Image to WAV file conversion with C and C++, ardunio, op amp, MOSFET, not to mention a turntable made out of card board.
Sparticles (author)  zawy1 year ago
Yes, but what I meant is a lack of experience and knowledge of the 'good' ways of doing it. Just a warning that everything should be read with a sceptical mind.

For example the electronics. People in the comments (e.g. ccrome' s comment) have suggested a far more efficient approach for the circuit that drives the LED's.

And the cardboard is basicly because I have never worked with wood and have no tools/skills to handle it . (yet, those will come soon or later)

And programming doesn't really count as 'technical'.
But there too I ventured into unknown terrain. I bet you could redo a lot of the C/C++ simpler with Python or Java.
ccrome1 year ago
Nice Idea!

I think there is something simple you didn't think of for driving the LED. You've set up your op-amp as a voltage source driving the FET open-loop, but you really want to use it as a current source, including the output current of the FET.

The way to do this is: rather than take your feedback from the gate of the FET, take the feedback from the top of the '123' ohm resistor. Simple as that. Output of the LM358A goes to the gate, and the '47k' resistor connects to the top of the 123 resistor. Now, it's a matter of setting the resistor values to get the current limiting you want.

Firstly, you probably want a rail-to-rail output op amp. There are lots of them, but the LMV358 should do fine. That V is good because it's rail to rail (i.e. the output goes from 0 to VCC).

Here is what I think the circuit should look like, along with the component values. Note: I added input protection so your headphone driver doesn't blow your op amp's input when it goes negative.
photo.JPG
Sparticles (author)  ccrome1 year ago
Yes, exactly.
Someone else suggested this in a comment below.
The thought that feedback can happen across the FET and op amp together didn't cross my mind. (I was already happy nothing became hot or started melting)
It is certainly something I will try out.

And I see you also noticed that the LED is drawn backwards in my schematic.
(So, to everyone else who reads this comment, in step 12, the LED in the schematic should be turned around)
I cannot edit it for a while since it is entered in the arduino and the rules don't allow editing after the deadline. But I will change it as soon as it is allowed.
ccrome ccrome1 year ago
Oops, here's a better image
photo (1).JPG
This is possibly the best Instructable I've seen yet! Logie Baird would have been proud of you!

I understand mechanical TV's - but there is nothing like building it yourself. Making the whole thing out of Cardboard is even more amazing!

Award yourself a Gold Star - (maybe on Mechanical TV!)
Sparticles (author)  simonrafferty1 year ago
Thanks!
loki20121 year ago
Nice! Something I always wanted to build, along with a camera using the same technology. Use different photodiodes to record Infra-red, ultraviolet? Not sure about the optics for these wavelengths. Again, nice job!
Same here...as for IR, it's tricky. You can't use glass lenses for deep thermal IR but you can use pin-hole optics, though not a huge problem anyway since you aren't going to get "true" IR without germanium or something unspeakably clever.
Sparticles (author)  jJohny1 year ago
Yes, somebody below suggested IR, it is a very intriguing Idea. And yes, the glass lens should be left out.

But the main problem will be the size of the holes, they are quite small so the signal will be very weak. But the wavelength of IR for thermal imaging is already of the order ~10µm. So attention will have to be paid to diffraction.

And also, the disc has a temperature itself, even more this temperature changes locally as the disc sometimes slides (friction) against the walls of the slit.

But it could work maybe.
jJohny1 year ago
Very, very nice. I've been procrastinating on something like this. It would really just be a demonstrator of the basic mechanisms involved for the camera and projection. Not as fancy and not recordable, no arduino or laptop. Just stepper motors synching identical paired discs, with LEDs and an op amp.

Here's something I suspect you'll want to try: replace the small holes with a thin spiral slit. As long as it's not dead center of the detectors view it *ought* to capture unique information (unless it's aimed at a blank white wall or fog bank.) You'll digital sampling
method -and probably any that isn't very fast- will cut way down on it's bandwidth and resulting picture quality but it might surprise. The simpler analog version might fairly good.

There isn't much out there I can find but I've read references to myriad variations on the Telivisor, beyond just different patterns used on the disc. Most tantalizing are so called "line-less" versions which I still haven't found info on but pondering it is where I got that idea for a spiral slit. The resulting image should be 'line less' after all.

Anyway, Thanks again for making this wonderful contraption and letting us know about it!
Sparticles (author)  jJohny1 year ago
Thank you too,

But a thin spiral will weaken the structure of the disk a lot. And it has to spin quite fast after all.
Also, you then sample over a line instead of a point. I don't really see how to distinguish the information of different points in that line.
gafisher1 year ago
Very nice! I built a Nipkow TV system as a science fair project in high school (1960s) using servo motors, neon bulbs and a photocell; yours is MUCH more elegant and, judging from your graphics, works quite a bit better.
Sparticles (author)  gafisher1 year ago
Thanks.
That image from Saturn is pretty much the best image quality I get. Displaying photos results in something unrecognisable.
-A-N-D-Y-1 year ago
So what's it made of? looks like some kind of metal or plastic?
Sparticles (author)  -A-N-D-Y-1 year ago
Pressed cardboard that is painted. (The title could've been a clue)
siafulinux1 year ago
A Nipkow like disk that John Logie Baird used to make the first mechanical TV like devices (experimental I don't think it ever hit shelves) just before Tube TV's came out.

Very nicely done. If you do as "John" did you could make a camera (same disk but with light sensor) that can send the images to the televisor. Eventually you might even be able to add color. :)
Sparticles (author)  siafulinux1 year ago
The original idea was to build a camera that's why it is so small and portable. But the signal was too weak. And noisy.
All I could detect was a 60 hz mains noise signal and couldn't get rid of it.
I'll have to increase my electronics skills first.
Hello, if I understand correctly you wanted to use this to *take* video. Your problem there is the major flaw of the Telivisor; it's looking through a key-hole.

The very first screentest of this tech in the US had the actor (Eddie Albert) in very *heavy* makeup to boost contrast and positioned under so many spotlights he almost passed out from the heat.

The disc blocks over 99% of the field of view at any moment, and so reduces the amount of light collected by that much. Naturally this signal will need tons of amplification to compensate. This will add a lot of noise itself that you'll need to filter out along with the signal from the power lines.

BTW, IIRC in Britain the broadcasters actually supported this tech with a 405 line color signal going out into the 1970's or later. Meanwhile 480i only had 23 lines of color, making the 405 actually look better if only during colorful scenes.
Beautifully crafted..even though it's made of cardboard....:)
I think you mean because its made out of cardboard
I should have been clearer, I think this is a brilliant piece of engineering and I just love that Sparticles made a few excuses of it is only cardboard. But you are correct 'made out of cardboard'.
Sparticles (author)  bricabracwizard1 year ago
Thanks!
ppowell141 year ago
Very Cool; BTW the original inventor was a Scotsman - John Logie Baird 1888 - 1946
Sparticles (author)  ppowell141 year ago
Thanks!
Libahunt1 year ago
Fantastic work with simply cardboard! :)
Sparticles (author)  Libahunt1 year ago
Thank you!
Nice to see a colleague.
Edgar1 year ago
Neat, voted and Blogged:
http://faz-voce-mesmo.blogspot.pt/2013/09/do-laser-para-fresa-engenhocas-pa.html
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