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First scanner build - progress

Benm

Benm

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I've recently started on a scanner, my first project of this kind.

I want to roughly follow what is outlined here:
http://laserpointerforums.com/f47/sound-card-dac-tutorial-40569.html

For the project, i plan to use a spacelas 20k scanner set (just arrived), the soundard dac, and a diy compensation amp and laser driver. I plan on using a ttl red and green setup, with about 200 mW for the red and about 50 mW for the green. No impressive specs, but it is a first project, so more orientation that seeking an impressive end result.

I got the soundcard: DealExtreme: $17.16 C-Media CM106 USB 2.0 External Sound Card Box with 7.1-Speaker SPDIF Optical Output and modded it for DC output. Using LFI, i've tried to put out a ilda test pattern to see what the voltages are actually like - see attached screenshots.
 

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Benm

Benm

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The first image is just the setup: laptop, usb sound card board, breadboard, and for now a direct connection to the scope. I'll build the compensation amp as a test on the breadboard, and eventually onto a circuit board.

As you can see in the DC output, the signal is offset about 2 to 2.5 volts from zero, which is to be expected. The AC component is about 1.5 volts, but i have to re-check if is this the maximum attainable volume.

As you can see very well in the next scope shot, there is no blanking on the image, making it look rather bad. Also, the scope is extremely fast compared to mirrors, resulting in discrete dots where you'd otherwise have the laser draw a line due to galvo/mirror inertia.

Next step: the compensation amp to remove the dc offset and amplify to 5 volts differential on the X and Y signals, and a TTL output for the lasers. I think i will power that from the +/- 24V supply that comes with the galvo set - via a couple of linear regulators.
 
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ElektroFreak

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nice! I'm looking forward to seeing your amp as it progresses.. It looks like you're on the right track.
 
Benm

Benm

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Time to put some rusty opamp design to work here. I have the required components on hand here, so i hope to find time soon to rig the correction amplifier. That part is fairly trivial though, i suppose the real headaches will arise when actually trying to get the galvos to do what i want them to.

Btw, does anyone have a ILD file that scans 8 degrees at 20 kpps, but with the full deflection range rectangle around it? I reckon most of the fun with this scanner will be projecting text and such at lower pps rates, but it would be nice to make it 20 kkps @ 8 compatible in the process if possible.
 
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ElektroFreak

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you should be 20k@8 compatible by default as long as your galvos are 20k galvos. The standard method of setting galvos for a certain kpps speed is to set it while running at 8 degrees. I other words, when you see a galvo set rated for 20k it's usually rated for 20k at 8 degrees.
 
Benm

Benm

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I know, but for testing its useful to project both the 8 degree test pattern, and a full deflection range square around it. See the attached file for an example at 30 kpps and 12 degrees.

The full deflection square is very convenient for adjusting compensation amps and such, since it allows you to set the gains to achieve 5 volt differential in a real world application (opposed to just maxing it out as DC with a wav file).
 

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ElektroFreak

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I see what you're saying.. but couldn't you do the same thing just by displaying the standard ilda test pattern? The outer square of the test pattern is at full deflection.. If you view the output on a scope it should be no trouble to tune the amp.
 
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Benm

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And here is the compensation amp, build on a breadboard for circuit testing. The left part of the board has 7812 and 7912 based voltage controllers, deriving power from the 24/24v scanner power supply (only takes a few 10s of mA).

The setup is typical, opamp operator with offset, and an inverter for both X and Y scanners, you can see part of the schematic doodled on the paper below.

Check the scope shots: After adjustments, it translates spot on to a zero-centered 5 volt signal (you are seeing only one half of the differential). Zoomed in, you can see the ilda test pattern center (still no blanking).
 

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Benm

Benm

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... and i couldn't resist just quickly wiring up the goodies from spacelas. The scan controllers run a little bit warm, nothing alarming, and the galvos make a nice little sound as they do their thing.

I just aimed a laser through it (~50 mW green), resulting in the pattern on the wall. There seems to be a lot to adjust, but for now i'll try to get the blanking to work first, and it now displays lots of lines that should not be there.

Well, so far so good.. I'll post back with the blanking stuff sorted out, and after that will take it from breadboard to a proper circuit board. In the end i will post all schematics for people that want to build one, but i'm not 100% sure they are correct for now.
 

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KiLLrB

KiLLrB

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Benm said:
... and i couldn't resist just quickly wiring up the goodies from spacelas. The scan controllers run a little bit warm, nothing alarming, and the galvos make a nice little sound as they do their thing.

I just aimed a laser through it (~50 mW green), resulting in the pattern on the wall. There seems to be a lot to adjust, but for now i'll try to get the blanking to work first, and it now displays lots of lines that should not be there.

Well, so far so good.. I'll post back with the blanking stuff sorted out, and after that will take it from breadboard to a proper circuit board. In the end i will post all schematics for people that want to build one, but i'm not 100% sure they are correct for now.
Click to expand...


So far so good! I need to get to reading/researching this looks like a good longterm project for the future :D Any reading material you guys suggest?
 
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ElektroFreak

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I like your idea of using the +-24V supply and some regulators for the correction amp power source.. Interesting way of doing it.
 
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Solonar

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Maybe use the other version of the ILDA test pattern(the one without the large box)?
 
Benm

Benm

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I've got a bunch of patterns to test with, so no hurry on this.

Even better, i got the blanking to work - and the test patters are getting better, projecting text is easily legible, but there are some distortions. As of now i'm powering a not too powerful red (at 100 mA or so) from the usb voltage, which causes some problems. The usb voltage varies a bit with load, resulting in distortions to the scanned patterns.

I've gotta rig a separate power supply to drive the laser(s), but this was in the planning already.

Also, i noticed the heatsinks on the scanner control boards get pretty warm after a while... Is this normal for spacelas scanners? I don't think they are getting dangerously warm (i.e. not boiling hot), but seems something that may need forced air cooling if i want to use any kind of enclosure for the whole project.
 
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ElektroFreak

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All scan amps get hot. Don't worry about it unless it instantly burns you.. normally the components needing the heatsink are rated to 150C. Bolting them to a larger piece of metal (ie case or baseplate) is more than sufficient. Fans are not your friends.
 
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Benm

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I sorted the blanking to some degree, and its doing its first runs:

YouTube - Scanner test

In reality you see the complete patterns being scanned, but due to the camera frame rate and youtube conversion they look broken to bits.

Things arent optimal yet, you can see its mis-scanning some parts of the projected patterns. I'll have to investigate further to see if it is the scanners, dac or compensation amp that is to blame for this. There are still adjustments on the galvo drivers that i have to try.

I'll try to take some photos of the 'problem', perhaps someone can easily spot whats going wrong here.
 
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