Inside my first mechanical television [built when I was 12]

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Inside my first mechanical television [built when I was 12]

Postby smeezekitty » Tue Jul 11, 2017 5:01 am

I dug this out of the shed yesterday!

It is the first mechanical TV I built when I was 12-13 years old. Honestly it was a terrible design. I made the Nipkow disk out of an old scratched up LP which was belt driven using a rubber band with home made pulleys. The "bearing" was a wooden hub with a nail through it. I am actually really surprised I was able to get a picture at all. At the time I thought it was the coolest thing ever though. It was also one of the first things I ever uploaded to Youtube.

Image

Image

Here is a short video of the disk spinning I took yesterday. Wobbling and all:


youtu.be/nHeHiwPH47g

Unsurprisingly there was no real sync. I powered the motor off of a wallwart through a wirewound resistor I made myself which would cause the disk to run at slightly below the sync speed and I had a momentary switch that would bypass the resistor. So I could alternately press and unpress the button to somewhat synchronize it.

And the first video I published of it working:


youtu.be/YL-Gz9tAkX0

Notice the lack of sync and poor Nipkow hole alignment.

The LED driver was just about as technically sound as the mechanics. I designed it myself without following any plans as I was just learning the basics of using transistors.
The first incarnations was just two yellow Radioshack LEDS, a resistor, 2 AA batteries and a transistor. The audio signal from the computer was just connected directly between the base and the emitter without any bias. The computer I was using was designed to drive unamplified speakers from sound card so it was able to put out over the 0.6V to turn the transistor on during the peaks of the NBTV signal.

I later improved about the circuit a little by upgrading to an array of 5 or 6 brighter red LEDs. I only used one 100 ohm resistor for all of them so the current is shared unequally (bad) and I also added a potentiometer to set the bias point for the base of the transistor (this worked kinda like a contrast control) as well as a coupling capacitor between the computer and the base. So it turned out to be almost a traditional transistor amplifier circuit. I think the addition of the bias was out of necessity because I used a different computer which couldn't output enough voltage to turn the transistor on. I didn't really have a good concept of bias and why it was necessary.

Yeah looking at it seems terrible now but hey I built it on my own based on internet research and actually got a picture. 12-13 year old me was proud of that.
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Re: Inside my first mechanical television [built when I was

Postby Steve Anderson » Tue Jul 11, 2017 4:13 pm

Very well done at the age of 12/13. When I was that age (late 60s, early 70s) I tried my hand at transistors and could never get anything to work. So I stuck with valve/tube stuff until a few years passed and I knew I had to get to grips with these newfangled devices.

I took my first job at Decca Radar in New Malden, Surrey, UK and was faced with the challenge of testing and fault diagnosing the first 7400 series logic. Talk about a steep learning curve! But it was the best classroom in the world and I'm forever grateful to that now unfortunately deceased company.

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Re: Inside my first mechanical television [built when I was

Postby Andrew Davie » Tue Jul 11, 2017 4:24 pm

I'm really impressed with this! You shouldn't belittle your work - great job and ingenuity for a 12yo. :)
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Re: Inside my first mechanical television [built when I was

Postby Klaas Robers » Tue Jul 11, 2017 6:01 pm

I am also impressed. When you are 12-13 as a boy, reading is still very difficult, not reading words, but understanding what their meaning is together. But what I am missing is: when was this? How many years ago was this for you?

I can recognise that there is some structure in the picture, but can't see what it is, what it should be. The holes in the disc ar far too large for that. Good that we see a photo with one of the holes: indeed, too large. And your way of hand synchronisation was clever thinking. We all started that way. Synchronisation is the last thing and the most difficult thing. First you should have had the thrill of seeing something.
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Re: Inside my first mechanical television [built when I was

Postby smeezekitty » Tue Jul 11, 2017 7:39 pm

Thank you for all the nice comments. And yeah I'm probably berating myself more than I should.

Very well done at the age of 12/13. When I was that age (late 60s, early 70s) I tried my hand at transistors and could never get anything to work. So I stuck with valve/tube stuff until a few years passed and I knew I had to get to grips with these newfangled devices.

Well I learned transistors first being born in the 90s and all, it is what surrounded me. But I actually do have an interesting in tube/valve equipment. In fact, I have repaired/recapped quite a few old radios.
I took my first job at Decca Radar in New Malden, Surrey, UK and was faced with the challenge of testing and fault diagnosing the first 7400 series logic. Talk about a steep learning curve! But it was the best classroom in the world and I'm forever grateful to that now unfortunately deceased company.

I can imagine. Going from hot cathodes to digital ICs would be a shock. There is a lot of difference between working with an analog circuit and a digital circuit...I actually find analog circuits more challenging because you often have to worry about things such as linearity. But I know a lot of people find analog circuits easier than digital circuits. To each their own.

But what I am missing is: when was this? How many years ago was this for you?


I made the first version around 2007 so about 10 years for me. Probably also about 10 years for you :mrgreen:
There were several revisions I made in 2010 after putting it on the 'shelf' for a while.


I can recognise that there is some structure in the picture, but can't see what it is, what it should be. The holes in the disc ar far too large for that. Good that we see a photo with one of the holes: indeed, too large. And your way of hand synchronisation was clever thinking. We all started that way. Synchronisation is the last thing and the most difficult thing. First you should have had the thrill of seeing something.


Thanks!
Yeah the disc holes are too large. I honestly don't recall how I knew where to drill the holes in the disc much less how I determined the size. I probably picked the size more or less randomly.

Is there any particular component you want me to take a better picture of?

Amazingly I found the WAV file for the original test card I used in the early video! Apparently I had posted the file to this forum in 2010 for some reason. http://www.taswegian.com/NBTV/forum/vie ... php?t=1047
I made the image myself and used Gary's video to NBTV program to convert it to the WAV. It was one of my favorite test cards because the shape showed it fairly well. I think it was the one I used the most during my testing.
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Re: Inside my first mechanical television [built when I was

Postby AncientBrit » Tue Jul 11, 2017 11:32 pm

Hi smeezekitty,

Great videos.
I particularly liked your video...


youtu.be/nHeHiwPH47g

Judging by the sound track there's an element of danger standing too close!
Well done, looking forward to seeing more of your work.

Cheers,

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Re: Inside my first mechanical television [built when I was

Postby smeezekitty » Wed Jul 12, 2017 5:55 am

Thank you Graham.
And yeah you're right. It has the tendency to break the rubber band belts and throw them at high velocity. That's part of the reason it has a top cover. Besides blocking external light, it contains flying debris.
It might be wise to use a pair of safety glasses if standing over it while it's turning :lol:

Taken today:

Image
Image
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Re: Inside my first mechanical television [built when I was

Postby Lowtone » Thu Jul 27, 2017 2:42 am

very impressive !
at 12 i was only able to build a magic lantern :lol:
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Re: Inside my first mechanical television [built when I was

Postby smeezekitty » Fri Jul 28, 2017 6:53 pm

Lowtone wrote:very impressive !
at 12 i was only able to build a magic lantern :lol:

Thanks! But erm...what's a magic lantern?
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Re: Inside my first mechanical television [built when I was

Postby Lowtone » Sat Jul 29, 2017 4:19 am

It's an old invention of the XVIII century, it works like a slide projector basically.
So you have paintings and drawings, and there are some animations tricks too.
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