
Full color laser TV - DanBC
http://hackaday.com/2011/12/31/full-color-laser-tv/
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julian37
The German company Schneider AG was working on a prototype for a laser TV in
the 90s. I remember reading an article about it in c't magazine back in the
day talking about an early demo where they projected an image onto a bedsheet
flapping in the wind with the image, of course, always in focus.

The article also talked about how the color gamut achievable with lasers is
much wider than the one available in CRT displays of the day and that the only
major roadblock to a commercial release was the (at the time) prohibitive cost
of blue lasers.

I was always hoping that the technology keeps getting developed but it seems
that it never went anywhere. Too bad, but all the better to see that hobbyists
pick it up now that lasers are much cheaper.

This Wikipedia article has some more information:

<http://en.wikipedia.org/wiki/Laser_video_display>

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julian37
Sorry for replying to myself but I forgot to mention the most amazing detail
about Schneider's design: the article was also talking about how you can keep
the lasers, cooling, power adapters etc -- basically, everything big and noisy
-- in a base unit that can be stashed away somewhere on the floor, maybe under
the sofa kind of like you can do with subwoofers. The light from the lasers is
piped to a projection unit through glass fibre. The projection unit then only
consists of the mirrors and some control circuits and thus can be miniaturized
down to almost nothing. So no need to hang a big apparatus from the ceiling
like you have to do with the current generation of projectors.

(I don't remember if this was actually implemented in their 95 prototype or if
it was just on the roadmap -- probably the latter.)

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jws
If you embark on your own, remember: It's all fun hacking until your 18 sided
mirror sticks and you dump that laser beam into a single spot and burn a blind
spot on someone's retina.

Make half the fun be the redundant safety systems.

~~~
Natsu
Just how bright a laser are they using? I would hope they're not using
anything bright enough to cause damage.

~~~
jws
You need to spread enough photons per second across the entire area of the
image to make it bright enough to see and look good. This translates into a
fairly good bit of light.

As a thought exercise, consider a ridiculously bright 3 watt LED flashlight.
Shine it through a 35mm slide to make a miniature projector. You now have
enough photons to make something like a 3 foot image. You are going to need
about 3 watts of laser to do the same job (no free lunch, except for green of
course). A 1 watt laser is more than 10 times the power needed to instantly
burn a permanent hole in your retina.

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Natsu
I can't find a wattage or a laser classification anywhere on the site. I
wanted to say that they don't make 1w laser pointers, but I decided to fact
check that first.

I was wrong, they do make "laser pointers" that powerful. Browsing their laser
safety forum has a post from a teacher wondering what to tell the parents of a
rich kid who is playing irresponsibly with a 200mw laser. Someone suggested
helping them find a guide dog....

And another person wonders if they should shine their 1w laser back at the
neighbors who shine 100-200mw lasers into their house and how may have injured
them. I honestly wonder just how far we are from a media frenzied panic that
gets nearly everything banned, safe or otherwise.

The voice of reason appears to be some inquisitive teenager, who appears to be
more responsible than everyone else. Forget age restrictions, someday we
should figure out a way to test how responsible people are and ban people from
doing stuff based on that.

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bane
I watched the video first, I was wondering how he kept the flicker off of the
display (laser display have notoriously slow tracking speeds that cause lots
of flicker the more of the screen they end up filling up as the beam has to
track all over the display). Filling up the entire screen with scan lines
might look atrocious.

Here's an example of a very nice laser demo that only gets flicker in really
complex scenes. <http://www.youtube.com/watch?v=m_CHXwXvWvs>

Then I paid attention to the writeup and picture and saw the device is just
swiveling a smaller set of mirrors. Very nice!

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tsotha
Discrete logic gates? I didn't think anyone used those any more. Seems like it
would have been much more practical to use programmable logic.

~~~
DanBC
This build is part of, I think, C'T magazines "build stuff from your stock
parts / junk bins" competition.

There have similar competitions recently; build stuff using 7400 series; build
stuff using 555 timers.

~~~
daeken
Let's say you understand the most basic principles of electronics, you've done
a good bit of programmable logic and microcontroller work, etc. How does one
go from that into discrete logic? Is the best way to just get a bin of crap
and start building?

~~~
DanBC
{most of this post is for the future people who happen to find it. You sound
as if you have most of this knowledge already.}

Yes. Get a breadboard and powersupply and some jumper leads and some LEDs and
start building stuff.

Then get some books; Code (the petzold book) and Art of Electronics are both
good examples to start really building stuff, and understanding what's going
on.

When you've got beyond the initial introduction you want to start using an
oscilloscope to start seeing things like leading edge or falling edge, and
measuring the times, and seeing how timing issues come in to play when you
have a long chain of slow logic gates.

Fun (as in puzzles and stuff) things to do include building one type of logic
gate using a different set of gates; use Karnaugh maps etc.

This is a really good way to get used to logic states and timing and using a
scope to trace a signal path and compare what you're getting with what you
think you should be getting.

Don't forget with real world builds to include de-coupling capacitors.

I was taught to create a memory map from a circuit diagram, which I guess is
handy if you're into that kind of low level stuff. (Probably embedded stuff
now.)

EDIT: Thanks to Shabble for the correction!

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shabble
nitpick: you probably mean Karnaugh Maps:
<https://en.wikipedia.org/wiki/Karnaugh_map>

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dhughes
Isn't this similar to old DLP projection TVs?

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notatoad
Yes.

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jxi
So, non-physicist here, but how does this fare energy, cost and
environmentally-wise compared to our existing LED, plasma, CRT, .. TV's?

~~~
daeken
It's worse in effectively every way, it's just an awesome hack.

