Homemade Scanning Laser Color Projector/TV

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Discussion Overview

This discussion revolves around the design and implementation of a homemade scanning laser color projector/TV. Participants explore the mechanics of laser beam deflection using mirrors, the modulation of laser sources for color images, and the challenges associated with achieving effective scanning techniques. The conversation includes technical details about the scanning process, potential issues with resonant scanning, and the requirements for color lasers and optics.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant describes a method using two mirrors to deflect a laser beam for scanning a screen, emphasizing low cost and power consumption.
  • Another participant raises concerns about the fast scan mirror, noting the need for quick line scanning and the challenges of achieving a return to the starting point within the flyback time.
  • There is a discussion about the necessity of using three color lasers and the challenges associated with obtaining a bright blue laser source.
  • One participant asserts that the scanning scheme involves alternating lines being scanned with inverted video content, while another questions how to achieve parallel scan lines with resonant scanning.
  • Concerns are expressed about the potential distortion of video content due to sinusoidal scanning, although it is noted that this does not inherently prevent parallel lines.
  • A suggestion is made that software could be used to linearize the scanning output, referencing a patented method for scanners that measure surfaces.
  • Another participant shares their experience with the difficulties of achieving linear movement in the slow axis due to inertia issues during flyback.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness and feasibility of resonant scanning techniques, with some asserting fundamental problems while others propose potential solutions. The discussion remains unresolved regarding the best approach to achieve parallel scan lines and the overall efficacy of the proposed methods.

Contextual Notes

Participants mention various technical challenges, including the need for precise timing in scanning, the limitations of current laser technology, and the complexities of achieving linear scanning. There are also references to specific frequencies and mechanical constraints that may affect the implementation of the proposed projector design.

kuntman
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In this project, by means of two mirrors (which can be tilted about two perpendicular axis) we deflect the laser beam so as to scan a rectangular screen and modulate the laser source to obtain a colored image on the screen. We don’t make use of sophisticated devices such as MEMS micromirror and acousto-optical-modulators.

Advantages of our technique are:
- Total cost will not exceed 10 USD in mass production. (Mechanical part costs only few dollars)
- Low power consumption (Approx. 4 W.)
- Pictures can be performed on any screen
- No lenses are needed for focusing
- Scanning had can be made as small as a cigarette box.

Max. speed of the fast axis mirror is 25 KHz. That corresponds to 50000 back and fro lines per second.
In order to make use of the conventional video signal, the resonant frequency of the present scanner is tuned to 15625Hz.
Therefore number scanned lines in each frame is 625. Refresh rate is 25 frames (50 fields) per second.
Vibrations of both axis are resonant, therefore sinusoidal.
Slow axis is driven by piezo.
Fast axis is elecromagnetically driven.
Laser modulation is analog.







http://www.photonlexicon.com/forums/album.php?albumid=104

And related videos on Youtube posted by sltvm2007 and sltvm2008
 
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The fast scan mirror is tricky
You have to scan a line quickly ( ie in 1/30*625 s) but then get back the start in one flyback time - can't remember what that is for pal but it's only about 1/50 of the line time
So you can't use a tuned resonant scanner, if you use a spinning mirror you need a huge f-theta lens

You will also need 3 colour lasers and some optics to superimpose them.
Red is easy, green is getting easier but solid state Ti-Sapphire (blue) replacements are still expensive, especially if you want watts of power which you will need to get a bright spot.
 
mgb_phys said:
The fast scan mirror is tricky
You have to scan a line quickly ( ie in 1/30*625 s) but then get back the start in one flyback time - can't remember what that is for pal but it's only about 1/50 of the line time


There is no trick
Scanning scheme is as follows:
First line of the first feld is scanned from left to the right.
Second line of the first field is scanned from left to the right with the video content inverted in time.
Same technique is applied to the successive fields which are scanned up and down and up...
 
Thats a good idea
 
kuntman said:
There is no trick
Scanning scheme is as follows:
First line of the first feld is scanned from left to the right.
Second line of the first field is scanned from left to the right with the video content inverted in time.
Same technique is applied to the successive fields which are scanned up and down and up...


I believe there is a fundamental problem with resonant scanning. How do you intend to get your scan lines parallel? You need linear, single-direction scanning to get that.
 
berkeman said:
I believe there is a fundamental problem with resonant scanning. How do you intend to get your scan lines parallel? You need linear, single-direction scanning to get that.

When the beam scans sinusoidally this does not mean that successive lines will not be parallel.
However the content of the video will be somehow distorted.

You may view the picture of scanned lines from the last link.
 
You can linearise the f-theta out in software to some extent.
This is patented (at least for scanners that measure a surface) - I had to design a multi resonant scanner system once to cancel out the effect without changing the timing.

For the vertical (field) axis you don't need to use a resonant scanner - an normal coil driven one is fast enough and the field flyback time is long enough,
 
I tried to make a linear slow (vertical) axis which uses coils etc. It is easy to actuate the mirror to move linearly, but it is almost impossible to stop it and get back to the starting point during the flyback time because of the considerable moment of inertia.
 
Thanks for sharing. It's really a low cost
 

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