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laser blanking

borgqueenx

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how is laser blanking achieved? is it software that makes it?
or is it the galvo's that support blanking?

i am going to install new galvos sunday and i hope they wont draw lines across the image.
 



anselm

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its usually the diodes driver that does the blanking...
 

andy_con

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you seem to not know the real basic about laser projectors, yet you want to do all this stuff - replace galvos buy moving heads etc...

would it not be worth reading up on things first?
 

borgqueenx

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you seem to not know the real basic about laser projectors, yet you want to do all this stuff - replace galvos buy moving heads etc...

would it not be worth reading up on things first?
experiencing is better then reading. im going to a LEM on sunday.

could you answer my question? ^^
 

andy_con

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if you say so...

what does going to the LEM prove?

whats the question?
 

borgqueenx

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my question was;
ah. so if my projector blanks now, it will continue to do so after the new galvo's are installed?
im going to the LEM to learn. there will be more people who will construct and edit laser projectors.
 

andy_con

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galvos have nothing to do with blanking and therefore changing the galvos wont affect the blanking in anyway shape or form
 

chipdouglas

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borg, it is the driver that controls the blanking via TTL or analog modulation. TTL gives you seven colors and anolog gives you the full array of colors. It is also in conjuction with the software you use. you have to set it up to send the correct signal to the driver. but the drive is the most important part of blanking.
 

anselm

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TTL gives you seven colors ....
What!?
Are you sure? Because if you modulate fast enough, even if it is only ON and OFF,
the eye gets the impression of varying brightness, allowing for much more than 7 colors...

Or am I missing something obvious here....? :thinking:
 

chipdouglas

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my scanner isn't operational but this is what i've read in multiple threads. and is the reason i opted for the flexmod drivers.

if you think about what you are asking, the lasers are all on or all off... there shouldn't be any overlap because lasers don't soft start. with anolog modulation you control the actual power of each laser to vary the brightness resulting in many more colors..

this is what i think i have learned from reading on the forum. so i am anxious to see if i actually did learn. input is more than welcome.
 

anselm

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with anolog modulation you control the actual power of each laser to vary the brightness
...and with digital modulation you control the EQUIVALENT power OVER A GIVEN PERIOD OF TIME.
If the period of time is short enough, the eye doesn't see flickering but the light simply dims
accordingly.
As you say, the diodes don't soft start, but power up and down immediately.
Persistence of vision, dude, think about how the movie theater works, and it's only ~24Hz.

I'm actually talking out of my ass here, since I don't have a laser with TTL modulation,
but I'm pretty sure that's how it works.

Otherwise TTL-modulation would be worthless, wouldn't it?

In the end, both types of modulation should have equivalent results, the main difference being the control signal.
OK I suppose if the scanning speed vs. (TTL) modulation frequency is too far off, I would expect some funny color flickering problems.....
With true analog, there would be no such problem.

Some projector veteran please chime in on this?
 
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chipdouglas

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ttl wouldn't be worth less. it is either on or off. and was around long before laser projectors. ttl in the laser world woul give decent beam shows.
 

vk2fro

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And analogue even better beamshows, as there are many more colours to choose from.

Analogue lasers are so commonplace now that software designers dont bother to include TTL-PWM mode in software. This mode describes the way the TTL laser can be pulsed at a varying frequency to trick the eyes into thinking its varying the light output. With the price difference between a TTL and analogue laser being nil or very small, its not worth the programmer effort, and this type of modulation would put extra load on the pc controlling the laser show.

edit: i need a new keyboard!
 

Cyparagon

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...if you modulate fast enough... the eye gets the impression of varying brightness.
This is true of a static beam, but scanned beams are not static. They are moving VERY quickly, and the modulation will just turn the picture into lots of dots.
Probably something like this:

 

anselm

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Probably ....
So I'm assuming it was not you who took that picture, right?
So how do you know exposure time, scanning frequency and modulating freuqency?

Also, unless the modulating frequency is a multiple of the scanning frequency,
those dots would be in a different place for every scan.
Your eye would still blur it into a line.

I get that TTL is inferior to analog, getting worse as scanning speed increases,
but I don't think it's as bad as you make it out to be....
I mean more than seven colors and no "dotted" picture.
 




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