Author Topic: Converting DMX laser to ILDA  (Read 404 times)

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Offline Jack

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Converting DMX laser to ILDA
« on: August 16, 2017, 10:00:49 am »
Hi guys, I'm new to the forum but have been interested in building a laser projector for a while now.
A little about myself:
- I live in Australia
- I study mechatronic engineering and computer science
- Im interested in lasers


It looks like there is a lot of knowledge on this forum and a good DIY attitude so i was hoping to get some advice on my project. Initially i was planning to build a laser from the ground up however today i found and bought a 2nd hand green/blue/cyan laser for $50. My intentions were to produce my own animations and have them displayed with the laser however the laser does not have an ILDA input and only has DMX. I am willing to completely tear out the electronics inside to use the galvos with a sound card DAC but im having some trouble understanding where all the pieces fit in. My current understanding is:
- LaserBoy software converts ILD files into WAV files which can be then fed into the sound card DAC
- Sound card DAC produces voltage (+12v to -12v ?) on however many channels are required (2 for laser blanking and 2 for galvo postioning?)
- At this point in the process i am unsure whether i can connect these channels from the DAC straight to the galvos OR if this is where the LaserBoy correction circuitry that James sells comes into play
- Whether or not i need the LaserBoy correction circuit would someone be able to briefly explain its function?


I appreciate any insight or links to information you guys have on the topic,


Jack 

Offline James

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Re: Converting DMX laser to ILDA
« Reply #1 on: August 16, 2017, 01:10:20 pm »
Hello Jack. Welcome to The LaserBoy Forum.

That projector may not have real scanners in it. It might have stepper motors.

Those are too slow to draw recognizable graphics. They are more for beam effects.

Also your lasers are almost certainly not analog modulated. That is to say they are either on or off. There is no in-between. So you only have 3 colors; green, blue and cyan (green + blue).

So, you might have a laser projector that simply cannot be converted to accept an ILDA signal set.

An ILDA signal set consists of analog signals for both the galvos and the laser modulation inputs.

The galvos take signals for X and Y from -10V to +10V max. This can be -5V to +5V depending on the sensitivity of the scanner amps.

The laser mod signals are from zero to +5V.

You are correct in the idea that there are several signals all together in a single wave file.

A modified sound card DAC has as many as 8 channels. Up to 5 of them are used to control a laser projector

X, Y, red, green and blue.

You need to modify the sound device because it is an audio device. It has capacitors in series with the outputs of each channel of the DAC. These caps block DC offsets on each channel. If you remove the caps, you end up with signals that are all positive voltage.

You need to remove or bypass the caps because you need absolute voltage changes from the DAC channels. You need to be able to play back a wave that has DC voltages in it. In other words you need to be able to hit a DC voltage and hold it for as long as it is set in the wave. The series caps would make that impossible.

So the LaserBoy Correction Amp does 2 things. It adds a settable negative voltage to the DAC signals so that they are centered over the zero volt line and it amplifies the signals so they reach the standard required voltages.

James.
LaserBoy is Sofa King Cool!
But it will never be Alpha King Done!

Offline Jack

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Re: Converting DMX laser to ILDA
« Reply #2 on: August 16, 2017, 08:21:23 pm »
Hi James, thanks for the quick response. Unfortunately you are 100% right about the laser using steppers, i hadnt really considered the fact that it might not have proper galvos. Just out of curiosity in a proper galvo setup is there just a negative and positive going to each galvo? Or are they more complex with mulitple windings and feedback signals

Offline James

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Re: Converting DMX laser to ILDA
« Reply #3 on: August 16, 2017, 09:34:25 pm »
Well yes and no.

Scanners are pure analog devices. They take differential signals (usually). Mine are old Cambridge and they are single ended. That is to say they only have a positive signal and a ground. Modern scanners have a ground, a positive signal and a negative or inverted signal for better noise rejection.

They have special amps that drive them. And yes, there is a feedback loop. The scanners indicate their position to the amp so the amp can get to where it needs to be.

I hope that makes sense!

James.
LaserBoy is Sofa King Cool!
But it will never be Alpha King Done!