Question about diy laser galvo scanner

I would like to build a laser scanner, but I have a few question before buying part,

I found a galvo kit online and after reading the sticked tutorial I found out i need : a digital to analog converter, a laser and it's driver.

for projecting indoor what laser power is enough ? what driver do i need for it ? is it possible to regulate the laser intensity or it is just on and off ?

the diy dac tutorial has a guide to correct the output of the dac but it's seems that it output +5v/-5v when the galvo kit require +15/-15 volt. Do i need to amplify again ?

thanks for your help. What driver you'll need is relative to the laser. Expect anywhere from 4V-30V at maybe a couple of amps. Probably best to just get yourself a small bench supply as you're only getting started.

I looked into the idea of building a galvanometer a number of years ago but to be honest for laser light shows there are so many options for such little money. Anything you build will be mediocre by comparison as they are finely tuned systems. I think the entry level 15/30 KPPS systems run for around $100 USD. Have a look at this.

As for DACs, have you ever messed around with microcontrollers before? You can buy ILDA driver cards but from what I recall the information on them seemed relatively obscure, the cards themselves expensive, and the inputs/outputs tended to be older RS232 protocols. Although now looking through ebay I see this which claims to be good value but seems very expensive for what it is (at least in terms of hardware). If you're looking for a project maybe playing around with an Arduino/embed microcontroller and generating your own analog drive signals might be a better project?

Oh, and a +/- 5V output will just produce a smaller image. You can set up an op-amp circuit to amplify the output of your DACs but you would need +/- 18V to get the max +/-15V out for your system. Again, where a decent 3 channel bench supply would come in handy. thanks a lot for your detailled answer,

Can you post a link to said tutorial?

this tutorial show how to correct the output of a sound card wich i plan to use to make the dac, i think i misread and the input of the said corrector should be +5/-5

laserpointerforumsXcom/threads/sound-card-dac-tutorialX/page-3#post- (replace the X with dot)

Have a look at this.

this type of kit is what i plan to buy, but it's not complete as the dac and laser is missing. I think I will follow your advice since I've already messed around with microcontroller and amp op.

but last question is for the laser, I wouldlike to know if it's possible to buy a higher powered laser and change it's intensity so i can use it both for light show and laser engraving or laser only function at a given power.

Yes, you can control the intensity but generally they don't have linear characteristics. It varies from diode to diode however, just be aware that it won't be a case of 0-5V ~ 0-100%. You can control them with PWM but you'll be momentarily be blasting 100% power which may be dangerous if it were to reflect sharply. Invest in some decent goggles.

So i guess for security reason it's better to buy 2 different laser. If I were to power one with a standard power supply, can I make the laser blink with a square wave to draw different point for example ? or do I need a special driver made for it ? This is just an opinion, but if you are having trouble with finding info, Going to a LEM would be super helpful for you. You would get to see many projectors from the home built to professional, firsthand (Once Covid-19 dies down)
At last years SELEM, Mariomaster had a homebrew laser projector he built with minimal parts and a thrown together cage, but the output was impressive for what it was.

If you want to know all about scanners:

Try Laser Scanners Book by Bill Brennan, president of Pangolin.
Pangolin currently make the best scanners in the world, Saturns
They are stupid expensive at $ a set by special order, if you can get one and that's only just for the scanners.
But they have the best specs and it gives you a high point to know what can and can't be done.

On the other end of the spectrum are the ultra cheap Chinese and home-brew. I picked up two sets of 10K Chinese scanners for $20 each at SELEM last year from D Kumpula. Complete with driver boards. He does a lot of builds and sometimes has leftover unused parts that are basically junk but fun to play with.

If you want to know about lasers:

Sams Laser BIble by Sam Goldwasser covers almost anything you want or need to know

Otherwise read these forums for the latest info on diodes and techniques.

Links below

LASER SCANNERS: Technologies and Applications: How they work, and how they can work for your product: Benner Jr., William R.: : Amazon.com: Books

Buy LASER SCANNERS: Technologies and Applications: How they work, and how they can work for your product on Amazon.com ✓ FREE SHIPPING on qualified orders

This link might help. It does need a scope for some portions. Almost all low cost scanners are clones of the Cambridge device shown here. Yours is a reduced parts count version with lots of changes to the power output stage. However I'm sure the position sensor portion and signal input will be copied exactly. That lets you find the scale factor and linearity pots based on the schematics. Your amp has no Polyfuse, fuse holder, or output jumper to lift the drive to the galvo coil, so that makes things tricky. I cant see where they brought out test point one or TP two for that matter, anything to save a few cents.... Section 7.1.2 is what I'm referring too...
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As you do not know the position sensor scale factor for your galvos, leave that part alone. Changing scale factor more then a few percent will result in a complete retune. Changing it too much can take you into a region where you cant tune well at all.
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You might also have an issue in needing a "clean" known source of the ILDA test pattern.... Your best hope without a Pangolin or LSX is to get in the PL Facebook page and see who is near you with one. I know one guy in Houston who might lend you some time on a QM system for tuning. I'm trying to find Dave's number, but I'm at work.
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I don't know how your system adds dwell, guide, or anchor points, if it does... Hence you need to be careful if using the ILDA test pattern.
If your DACs are not double buffered, updating at exactly the same time, you may see some skew in the images, or have real trouble with the circle in the square.
Beginners often try to tune at too wide a scan angle, too.
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In that case, if you suspect your test pattern is off the reservation, revert to the Laser Media test pattern till you get close, my sequence is Quadrature Square, ILDA, Grid, LM, repeat...
The LFX patterns are fine... Its just your software may not follow some traditional steps when dealing with the output waveforms.
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Make just small changes, or you might find yourself very unhappy....
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http://www.skywise711.com/lasers/scanner/scanner.html
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Skywise is kind enough to host that for me...
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The above factory initial setup is a laboratory scanner amplifier procedure, it does anything but get you a clean ILDA pattern... In fact it will turn a good ILDA tuning into a very fast rise time tuning that you would use for a lab or factory scanning setup. However it is the best cold start procedure (Well, its the ONLY one!) when your lost and have to come up from zero. Ignore the parts for the old G120 amps, the document is blended...
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Easiest way to quickly set the linearity is to attach a true RMS voltmeter while projecting a centered, symmetrical test object and adjust for least RMS AC volts at the feedback sensor output.
Its not the best way, but with what you have to work with, its a start. To do it well requires a digitizing scope.
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If I'm sure I'm using a meter that will not kill opamps, I measure the potentiometer resistances before I make big changes. (system off, of course!) Because they are "In Circuit" , you'll see all sorts of non-linearity on the Ohm Meter.
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I'm jammed up today, but I can help later in the week. Find Buffo's tuning procedure here on the forum, its not my favorite way, but the "three legged stool" method works well for beginners...
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Finding Eight Degrees for the ILDA pattern:
https://pangolin.com/userhelp/scanangles.htm
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Steve

Gah! I accidentally deleted my previous post while trying to edit it to correct some typos I noticed (beware the mobile version of the site!) - I was able to copy the text on my , will re-enter the message for posterity when I get home, by appending to this one.

Here's the message that was in between 3 & 4 above
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Hi Steve,
Thanks for the response.

Yes, I can read schematics. I'm no EE, but I can generally make them out OK.

What do you have in mind? (I don't have schematics for these boards- but maybe you do for some board where the pots are known?)

Also, I have made some progress since my first post. I've tentatively identified the six pots in a row, and while I'm not positive about two of them, I'm reasonably sure about the other four.

I'll try to attach a picture later - I can't figure out how to do it from the mobile interface to this site.

That said, I still have concerns, because even knowing (100% sure on gain and LFD, 80% on HFD) which pots do what, I'm having trouble tuning. I have certainly hosed up some of the other settings, and don't know if they may be related to my issue.

So far, after two tries, I can't get the circle centered in the center square. I can get it round, and just barely touching on the right and bottom, but then the top and left are approx 5% shy of touching. If I tune to get them touching, the other two sides extend beyond the square's sides. (I'm only using a single laser at the moment, so it can't really be an RGB alignment issue.)
It kind of makes me wonder if the test pattern I'm using is not quite right. (I got it from the laserfx web site.)
I don't have a pic of that at the moment. But I can get one later if that helps.

Jason

Steve,
Thanks for the detailed response!

I'll have to provide a more thoughtful reply later, from home, but quickly:

• I do have a digital 'scope. Nothing too fancy, but seems adequate for this task.
• "I don't know how your system adds dwell, guide, or anchor points, if it does..." If by 'system', you mean my Arduino and the software it's running (I.e., not the galvo drivers, galvos, etc), it doesn't add any of them. I don't know what they are (though the names give me some hints).
  That's sort of a topic to itself: Not knowing how ILDA patterns are meant to be processed, and armed only with a link to a document detailing the file format, I naively just pull out the coordinates and the blanking signal, and turn them into data that I used to manipulate two DACs and one digital output. It attempts to output the points at the correct cadence (I've been using 20kpps, knowing the pattern is intended for 12/30k, but not really sure what that actually implies.) Also naively, when I see the blanking signal is high/true, I 'blank' immediately (it's a dollar store pointer... there's no blank, I just cut power to it), and then move to the coords associated with that state. I'm not sure if that's right (vs going to that blanking state after arrival), but assume from the output I'm seeing that it's correct-ish, at least. That leads nicely to your next point, which was a face-palm moment for me...
• The DACs are NOT buffered. At one point I was considering that I might have been better off buying a separate DAC chip with a sync signal (rather than buying a 'duino with dual 12 bit DACs - true, not PWM) for that very reason. As currently programmed, I'm outputting X first, and then Y (or vice versa - need to double-check the code). I'll just bet that's key to the off-center issue. I'll try reversing the sequence and see if that moves the circle. I'm not sure what the delay is between one being set and the other, but it's on the order of microseconds, but, considering I'm only adding a 29-30uSec delay to each point to achieve 20kpps, I have to assume that a significant part of the remaining 20-21uSec is being spent on each DAC write. Maybe 5-10. So, it could totally skew the circle as I'm seeing if they aren't happening as intended.
• Not sure I completely follow what you're saying about setting the linearity (or where I find the feedback sensor output, but guessing some time spent reviewing the document you linked will help with that.
• Actually, Buffo's doc is what I've been using so far I have an ILDA Test Pattern file, I've faked my own Quadrature file, based on what the image showed (entered coords, ILDA-style, then run through my showIlda() function), but I have no idea if I got it right - I only entered coords for the corners, not sure if there should be intermediate points as well. It also doesn't look perfect, but it seemed to serve the purpose of doing the first bits of the tutorial faster than the ILDA Test Pattern. I haven't got a copy of the Laser Media Test file, and haven't tried to make one.

That's what I have for now - I'll repost the other post later, and read the links you've sent tonight.

Thanks again,

Oh, and an aside: In learning about the file format, I learned that it supports 3D. I originally thought maybe that meant for 3D visualizations, but wasn't sure how that was meant to work. The whole thing kinda made me cock my head to the side. Fundamentally, it's still 2D, even if the artist makes it 'look' 3D... I just learnt yesterday that some galvo systems include facilities for controlling the focus point of the laser as well. Is that what the third dimension is actually used for?

Jason

I'll get you definitions of the point types. I need to scan in a document that is not on-line anywhere. While a 3D frame is ultimately projected as a 2D calculated object, storing it in 3D has certain uses, including adding foreshortening, real time manipulation, etc.
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I'll get you a test frame bank file. I keep one on a USB stick at home.
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If your scope had at least 1 Mhz of bandwidth, you can see what you need to see. After all, max frequency content of a 30K test frame is a bit over 2.5 KHz... At 30K, you can see subtle errors in the DAC updates, but your close enough for now.
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Locate and bring out TP1 (Position Sensor Output) if you can, its very useful. TP2 is ground anyways. It also helps to look at the Galvo current, which is at the high side of the 0.1 Ohm output current sense resistor.
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Linearity can somewhat screw up the Circle in the Square on the ILDA test pattern if its off. Its sort of the dynamic balance of the position sensor, which is two or more photodiode pairs. Normally one does not need to ever touch that potentiometer, if the factory totally screwed it up, it can affect your test pattern. Its a very subtle adjustment. I would not worry about it.
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Your processing of the frame is "correctish" as you say. Your not that far off....
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A Quad Square is usually 2-3-4 successive points at the corners of a sharp square wave, goal is to make a 30 to 50 Hz square with no intermediate points for fast risetime to excite ringing in the galvos for tuning. A well tuned galvo will show almost no overshoot or undershoot at the corners of a Quad Square.
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Some lite reading:
http://www.photonlexicon.com/forums/...ILDA-STANDARDS
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Steve