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Old 06-05-2014, 09:55 PM #1
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Default Simple Galvo set - Requirements & Possibilities?

As I described in my welcom thread, I recently built a very simple XYscanner with some speakers. I liked it quite a bit, but wasn't happy with the quality. (LOTS of noise, it worked only kind of properly near the speakers resonance, only stereo audio input, etc)
I'd like to play with this (a lot) more, so I'm considering to buy a simple XY-scanner set in order to be able to play more / better with it, without having to worry the whole setup generally breaking apart from vibrations and other hardware related issues.

The set I was looking at can be found here:
"Click me, Click me!"

I'll admit that I'm not too sure about what I should be looking for. This looks pretty neat, and has everything I need - as far as I can tell. (I do have a simple 5mW laser to start with, if I like it enough I'll buy a better one, but not yet)

My main question though is about signal input. For my own rig I just used speakers and audio, but that'll be more complicated in this set. Will I need (an)other component(s) in order to be able to make simple images? Think about lissajous-figures, with multiple waves of different amplitude, frequency and phase (might write the program for that myself) and just some simple animations. (So simple that it's (almost) possible to make them by hand by just writing down X, Y and timestamp or so.)

Any nudge in the right direction would be greatly appreciated! I'd love to buy this set and have some fun, but I don't want to spend ~€100 only to discover I need €500 more of equipment to get the most basic stuff to work. (Yes, I know, lasers can be expensive, but I just want to 'taste' first)

Thanks a lot!

EDIT: I also have an Arduino, which I'm sure will come in handy somewhere, if that makes any difference.



Last edited by Svenvbins; 06-05-2014 at 09:57 PM.
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Old 06-05-2014, 10:10 PM #2
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Default Re: Simple Galvo set - Requirements & Possibilities?

They take analog signals, meaning you'll need a DAC in there somewhere to interface it with an Arduino. They take a 0V to 5V signal.

This guy would probably work, one for x and one for y.
http://www.adafruit.com/datasheets/mcp4725.pdf
it's already got an arduino library here:
https://learn.adafruit.com/mcp4725-12-bit-dac-tutorial

That galvo set is a good starter set, but keep in mind they may be a little fiddly to get set up and tuned since it's a cheap set.

Last edited by ARG; 06-05-2014 at 10:11 PM.
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Old 06-05-2014, 10:36 PM #3
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Default Re: Simple Galvo set - Requirements & Possibilities?

Quote:
Originally Posted by ARG View Post
They take analog signals, meaning you'll need a DAC in there somewhere to interface it with an Arduino. They take a 0V to 5V signal.

This guy would probably work, one for x and one for y.
http://www.adafruit.com/datasheets/mcp4725.pdf
it's already got an arduino library here:
https://learn.adafruit.com/mcp4725-12-bit-dac-tutorial

That galvo set is a good starter set, but keep in mind they may be a little fiddly to get set up and tuned since it's a cheap set.
You guys are awesome. Posted a similar question to photonlexicon (saw a link to there somewhere on here) and basically got a hocus-pocus answer no-where near what I (thought) I needed

Seems like the Showcard in that set doesn't do anything special and that the +-5V signal is the real input, as I originally suspected. Thanks for verifying. The DAC-info definitely is useful as well! Didn't realize that wasn't on the arduino by default.

I've got two follow-up questions, and if they're answered as well as the previous one I think I'll be ordering some things this week

1) As far as my circuitry / driving knowledge goes, I could still use the audio channel from my laptop as the signal, right? In that case, that might even be easier for me, since the sound card is one huge DAC after all, and together with my (sufficient) knowledge in programming I guess I could fiddle with producing sound files containing "galvo coordinates". (I can't see why this wouldn't work, but since it's a new area to me I figured I should verify)

2) Related to 1). I don't mind fiddling a lot with 'writing' animation stuff from scratch (and probably learning a lot in the meantime), but I was wondering whether there are any open source / free programs you know of that don't use the 'exotic' connectors and plugs I don't have
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Old 06-05-2014, 10:40 PM #4
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Default Re: Simple Galvo set - Requirements & Possibilities?

1) You would be better off buying an external sound card to mod, and creating a driver to go with it.
See: Sound card DAC tutorial

2) Not sure what's out there in terms of open source programs, maybe laserboy is open source?
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Old 06-05-2014, 10:48 PM #5
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Default Re: Simple Galvo set - Requirements & Possibilities?

Quote:
Originally Posted by ARG View Post
1) You would be better off buying an external sound card to mod, and creating a driver to go with it.
See: Sound card DAC tutorial

2) Not sure what's out there in terms of open source programs, maybe laserboy is open source?
Thanks! I'd seen the link you provided before, but didn't realize I'd need the DAC back then so disregarded it. (Figuring I'd use my laptops output)

I'll have a read tomorrow, time to get some sleep now.
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Old 06-06-2014, 07:22 PM #6
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Default Re: Simple Galvo set - Requirements & Possibilities?

Well, I've read through some more threads and will be ordering the galvo set tonight. I'm convinced I'll have enough fun for my money at this stage

In the meantime, I've come up with some additional questions.

- Do I understand correctly that using my laptops soundcard as-is for e.g. lissajous figures, but not for anything that requires a DC-signal? (I read that some capacitors need to be bypassed on the card, which is why people mod external cards?

- Correction amps are just DC-DC converters that convert the soundcard output to a (higher) voltage that's accepted by the galvo set?

- If my galvo set only accepts -5 to +5 V, a correction amp wouldn't really be necessary, right? (I think that's standard audio output?)

Cheers!
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Old 06-06-2014, 07:57 PM #7
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Default Re: Simple Galvo set - Requirements & Possibilities?

Don't know about the other questions, but the correction amps are for tuning and driving the galvos. IIRC it's essentially a power amplifier.
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Old 06-07-2014, 07:51 AM #8
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Default Re: Simple Galvo set - Requirements & Possibilities?

Audio outputs have capacitors on their outputs that block DC signals. You need to connect to the output prior to those capacitors. The sound card DAC tutorial thread, once you wade through all the shit-posting, actually has a lot of good information about sound card DACs, correction amps, and even how to create analog laser drivers.

You can't use the output of the sound card directly to drive your galvos. The sound cards depend on those output capacitors to filter out the DC, and without them, they have minimum voltage levels that are above ground reference, usually from ~1.25V for the negative peak of the waveform, to about 4.5V for the positive peak. Galvos work with a -5V to +5V differential input voltage. The correction amp allows you to take the voltage output range of the sound card (or any input you may choose to use) and adjust the output range and offset of the output for the galvo set.

Likewise, you can make correction amps for tuning analog laser outputs too. There are correction amp designs and analog laser driver designs in the sound card DAC tutorial by Benm that I use all the time.
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Old 06-07-2014, 11:40 AM #9
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Default Re: Simple Galvo set - Requirements & Possibilities?

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Originally Posted by Bionic-Badger View Post
Audio outputs have capacitors on their outputs that block DC signals. You need to connect to the output prior to those capacitors. The sound card DAC tutorial thread, once you wade through all the shit-posting, actually has a lot of good information about sound card DACs, correction amps, and even how to create analog laser drivers.

You can't use the output of the sound card directly to drive your galvos. The sound cards depend on those output capacitors to filter out the DC, and without them, they have minimum voltage levels that are above ground reference, usually from ~1.25V for the negative peak of the waveform, to about 4.5V for the positive peak. Galvos work with a -5V to +5V differential input voltage. The correction amp allows you to take the voltage output range of the sound card (or any input you may choose to use) and adjust the output range and offset of the output for the galvo set.

Likewise, you can make correction amps for tuning analog laser outputs too. There are correction amp designs and analog laser driver designs in the sound card DAC tutorial by Benm that I use all the time.
Thank you so much! Didn't know regular soundcards had this problem (or rather, property), this clears up a lot of things. And you're right, while the info is there (in the DAC tutorial thread as well as some others) , it seems to be rather dispersed.

I've ordered the scanner set, so now I'll just have to wait 2-3 weeks for it to arrive, and learn more in the meantime. It comes with 2 galvo drivers, and the description says
"Driver Adjustments: Gain,Size Position,Linearity,Damping,Servo gain"
I'd say this includes the 'rescaling the input/output voltage' that the correction amp does, but I'm not sure whether it also deals with the DC offset? As in, I'll need a soundcard DAC anyway, but will I need the correction amps as well or is everything I need included in the drivers?

If you don't know, I'll see whether I can buy all the correction amps components at the electronics store at uni
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Old 06-08-2014, 08:29 AM #10
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Default Re: Simple Galvo set - Requirements & Possibilities?

The soundcard DAC tutorial, as with all threads on this forum, used to be a lot nicer before Coldshadow reduced the number of posts per page. Now you have to wade through multiple pages to find what you want. It used to be that those correction amp diagrams were on the 3rd page, but now it's a bit further in.

For the driver tuning, no, those settings affects the scale/offset for the galvo's PID feedback driver that performs the positioning. The driver itself expects to have a +/-5V differential signal inputs and you'll need to provide that regardless of what settings you change on the driver itself. You might be able to get away with just tuning the driver itself (usually it works okay out of the box) if you had a signal source that provided the +/- 5V differential voltage, but a soundcard DAC will not do that, so you need the correction amp regardless.
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Old 06-08-2014, 09:17 PM #11
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Default Re: Simple Galvo set - Requirements & Possibilities?

Thanks. The small amount of posts/page was one of the first thing I noticed here, and have been looking for a setting to change that, but it seems like it's a forum setting after all then.

The link in the soundcard DAC tutorial to the actual soundcard is broken. I found a post some pages in linking to its ebay page - which is broken too - but the search terms gave me an idea of what to look for. I think this card is very similar, but there's one thing that's bothering me:

"Only R L channel PCM audio in 5.1 channel can be conveyed in digital playback mode. In analog playback mode, it supports 6 channels codec for analog playback"

Is the 'digital playback mode' something fancy we don't need? Because 3 channels at the least (X, Y and some sort of TTL on the laser) would be nice. I'd say analog playback is the standard?

Aaaand more. I should be able to produce the correction amp by BenM without problem, but would there by any chance be a similar schematic / help on how to turn the laser diode on/off with the sound card? I'm pretty sure it's just with a transistor, but I don't have a clue on whether you can get all the required power through the single transistor?

I do realize I'm asking quite a lot of questions by now. Please bear with me, and I promise to merge everything into an (updated) "Step by step laserscanner" thread for those interested!
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Old 06-09-2014, 08:08 AM #12
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Default Re: Simple Galvo set - Requirements & Possibilities?

I think the digital playback mode means digital data, PCM 1s and 0s, like you'd get over a digital audio cable, not analog. You only need to care about the analog playback for producing a fixed voltage in this case; therefore it shouldn't be a problem.

I've used this USB soundcard and it works just fine. Note that so far the drivers on Windows 7 suck. I've only been able to use all seven (7) channels on Linux. Maybe you'll have more luck.
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Old 06-10-2014, 01:50 AM #13
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Default Re: Simple Galvo set - Requirements & Possibilities?

Here is the direct link to Benm's correction amp schematic, and here is the link to the current controller for analog modulation of lasers. The laser current controller linked above functions as a correction amp, so you just need to connect it to your soundcard and make the adjustments.

I also use this circuit for regulating current to my laser diodes. It can also be analog-controlled by varying the voltage to the gate of the MOSFET.

Note that with all these transistor-based analog laser drivers, the transistors are in linear mode, so they act like resistors. This means that they will also get really hot and may need to be heatsinked depending on the current.
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Old 06-17-2014, 12:42 AM #14
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Default Re: Simple Galvo set - Requirements & Possibilities?

Quote:
Originally Posted by ARG View Post

2) Not sure what's out there in terms of open source programs, maybe laserboy is open source?
Openlase is a opensource library for generating and displaying laser art. It's typically used with a sound card DAC and correction amp or you could use the Lasershark DAC. Lasershark is an opensource laser DAC that was designed to work specifically with Openlase.

Links:
Openlase Blog
Openlase Source Repository
Lasershark
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Old 06-17-2014, 09:28 PM #15
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Default Re: Simple Galvo set - Requirements & Possibilities?

And another post starting with "Thanks"
Openlase looks really interesting! I'll have to read into it a bit more, but I'm sure that'll happen. In the meantime I've played a little bit with the show card that came with the galvo's, I was surprised it was even more plug&play than I'd thought! Now I'm just waiting for the sound card, and the great adventure can begin.
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Old 06-28-2014, 10:54 PM #16
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Default Re: Simple Galvo set - Requirements & Possibilities?

Here used to be some rant about my self-built correction amp not working

FINAL EDIT:
(Removed all the other stuff)

I figured it out... First mistake was taking the wrong pin order. Didn't manage to remove the chips from the board (8 soldered pins... :P) so took one from my spares - not noticing THAT one actually was a different IC... I feel so blonde! Anyhow, it's working now. Just have to find another TL082 somewhere in the lab
Do have one question related to grounding though. My supply has +15/ground/-15V, my soundcard +5V and ground. (maybe more, but that's not important). What I don't understand is how they're related:
* When soundcard and supply are NOT connected to the circuit, ground_soundcard to 15V_supply gives 0V, and ground_soundcard to -15V_supply gives 0V as well. Shouldn't there be a voltage difference, even when the grounds are not connected?
* When connecting supply & soundcard as instructed, using the soundcards ground, the voltages read ground_SC to +15V_supply=0V (still), ground_SC to ground_supply=-15V and ground_SC to -15V_supply=-30V. In other words, the ground of the soundcard is pulled towards the +15V of the supply? How scared should I be for my soundcard / laptop? (Am using an external USB sound card)

For the record, the ilda outputs now have different polarity and work perfectly, despite the problems/questions above.

Last edited by Svenvbins; 06-30-2014 at 09:25 PM. Reason: Solved something =D
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