Homemade Scanning Laser Color Projector/TV

[Benm]

Somehow i think that will get on my nerves... the noise from a 15.625 Khz flyback in a crt irritates me at times, and this is wizzing around at half that frequency. Then again, proper galvo's can be quite noisy too, depending on what you are scanning.

I think its a creative idea though. Sure, its a tuning fork with a mirror attached, but as long as it actually works, why not?

I've never tried to use scanners as a projector, but somehow i think it might be possible with and ordinary galvo set... perhaps even right off the VGA analog X and Y signals with a (pretty fast) correction amp in between. In a real life system you would scan zig-zag rather than each line left to right, but that only reduces performance by half at most.

 

[LSRFAQ]

Enjoy the 16.25 or 15,570. Some place around 35, you stop hearing it!

I'll get my hat and coat....

Steve

 

[sltvm2007]

About the noise: Reply to Benm

Somehow i think that will get on my nerves... the noise from a 15.625 Khz flyback in a crt irritates me at times, and this is wizzing around at half that frequency. Then again, proper galvo's can be quite noisy too, depending on what you are scanning.

I think its a creative idea though. Sure, its a tuning fork with a mirror attached, but as long as it actually works, why not?

Noise of this scanner can be eliminated in several ways:

1. Keeping the fast mirror in an evacuated box. (This will incease the performance many times.)

2. Increase the frequency above 20 KHz. But this time you cannot make use of the conventional TV video signal as an input. Now, you will need a video signal running at that speed. This can be accomplished in a very simple way:
- Take a cheep Made in China game console
- Increase the clock frequency by either replacing the XTAL of the gadget or by feeding it from an external oscillator. You can make an variable fequency oscillator if you wish.

There is a picture of such a system below. You can see the external XTAL oscillator on the rhs of the board.

For some images pojected by this gadget:
http://laserpointerforums.com/members/sltvm2007/albums/homemade-laser-scanner/

 

[Benm]

I suppose increasing the frequency wouldn't be much of a problem - as long as you power it using a pc you could hook it up to the VGA port and play with output framerate and resolution. For 640x480 @ 60 Hz you would end up with a line frequency of 28.8 kHz, well beyond the audible range. Downside is you'd need petty fast scanners to keep up with that at any serious projection angle.

Its not something i'd spend much money on though - if you want to project tv, get a beamer

 

[sltvm2007]

with this techique, we achieved vibration frequencies as high as 25 KHz and total optical deflection of 30 degrees

 

[dasraiser]

could this be done with high speed motors (just spinning) n mirror (aka liquid sky) but attach a rotary pot to the motor shaft connected to a schmitt trigger to locate the raster position?

[edit]

hmm yes rpm faaar from khz lol

 

[kingbowser]

Great work!

Now the biggest problem is the laser modulation: using PWM you need a ridiculous frequency (about 2MHz) in order to fully modulate 256 levels of color at a scanning frequency of 7800Hz. Another possibility is to use a mechanical modulator, but it needs to be very precise and fast enough. Another possibility could be the combination of 8 lasers per color, but it would be expensive and difficult to mix (each laser is binary controlled and output 2^N lumens). Any idea? It's a PITA not to have a pure green laser :-(

 

[dasraiser]

Great work!

Now the biggest problem is the laser modulation: using PWM you need a ridiculous frequency (about 2MHz) in order to fully modulate 256 levels of color at a scanning frequency of 7800Hz. Another possibility is to use a mechanical modulator, but it needs to be very precise and fast enough. Another possibility could be the combination of 8 lasers per color, but it would be expensive and difficult to mix (each laser is binary controlled and output 2^N lumens). Any idea? It's a PITA not to have a pure green laser :-(

the raw video feed would modulate the laser with its analogue signal, just requiring simple amplification to match your lasers power requirement.

 

[kingbowser]

Yes, but green laser isn't as easy to modulate, as it's not a pure laser source but it comes from another wavelenght. Red and blue (or violet) are simple to modulate the way you are talking about, but green is different, it requires an advanced control.

 

[dasraiser]

modulating the IR pump will produce more or less photons, in turn adjusting the output intensity.

im sorry if i cant see the problem, maybe you could enlighten me with more of an explanation.

 

[dasraiser]

hmm, thought just occurred to me, if u say used the dummy load in parallel to the LD and modulate a cross fade between them, would this make a nice modulation source as it will keep the driver constant?
not sure what circuit could be used, or if theres an IC that could do that, keeping the load ratio on the sweeps constant.

 

[sltvm2007]

Reply to kingbower and dasraiser


Contrary to the common belief, DPSS green lasers are susceptible to high speed analog modulation.

You will find below a diagam of a drive circuit.

And there is a picture of a green image projected by using this circuit.

 

[kingbowser]

It's really this simple?!? Wow!
Have you a video of the projector working? What is the maximum resolution/frequency you reached? It's very, very interesting, in the future I will build it. From which source are you supplying the analog signal? Well done!

 

[dasraiser]

from this if i used a red LD with 2.8Vf the transistor must then have a 6.2Vf? (9v Vcc)

not sure how a constant current source like the DDL will cope with this, it may try to make up for the loss with more voltage? can you please help me and explain this circuit (learning on the fly ), or what current/voltage the diode experience on min/max video signal?

could you use an opamp with the constant current going to the VCC and have the diode on the output with video on the input? or will this also have the same affect on DDL?

also not sure if u can drive opamps with that low a voltage. tho u could use voltage divider on output, but thermal variation may happen if divider network gets too hot :thinking:

only ideas, sry if this is barking up the wrong tree ive got so much to learn and it grows everyday :cryyy:

 

[sltvm2007]

not sure how a constant current source like the DDL will cope with this,

I don't mean ''constant current source'' anywhere. It is a voltage source with a current limitter in order to protect the laser diode. OK?


Reply to kingbowser:
There are viddeos in youtube
write sltvm2007 or sltvm2008 in youtube search

Video signal comes from DVD

 

[dasraiser]

true, you pic mentions current limiting, so the transistor is acting as a voltage divider?

but i didnt question your Vcc source, i was wondering what voltage/current your diode experience on MAX/MIN video signal, and if the DDL constant current circuit would work.

what driver do you use? im using DDL
im curious as im in the process of building (well more like formulating at moment) an R scanner :crackup: (i have no G DPSS or B diode) and i want analogue modulation, your idea has me intrigued, maybe when my understanding of electronics grows i will have more of an insight.