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Author Topic: Switching Laser Module With Arduino  (Read 2794 times)
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Hi all,

Im quite new to the laser topic (but not so new to electronics and arduino) and I'm looking for a possibility to switch a 100mW laser module on and off with arduino in something like a DIY laser cutter.

cr0sh wrote in another thread:
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Basically, think of a laser module as a 3 volt DC motor; the interface (using a simple transistor/mosfet/darlington driver circuit) is the same, you could even easily hook up a small cheapo keychain laser from your local dollar store and run it this way.

Is this so easy? Or do I damage the laser when turning it on and off in this way often?

Does anyone know a diagram, showing circuits with lasers and arduino involved, so I can build it myself completly with a laser diode from an old dvd burner?

Thanks for some advice!
Christian
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in something like a DIY laser cutter.
100mW would not work in a laser cutter. All it would do is burn/melt whatever you wanted to cut. I would say you would need at least 1W to do paper without burning it all, probably more than that.

Mowcius
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Thanx for the reply.
There are many storys on the internet about cutting with 100mW or at least with DVD-burner Diodes. On ebay they sell laser modules with 260 mW explicitely for cutting (up to 0.8mm paper).
But maybe you're right and these are only stories. Anyway, I will give the thing a try.

The most important issue for me is turning the laser on and of. An I think, turning on and off the supply voltage is not the best way.

christian
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These lasers are nothing more than slightly differently constructed LEDs, with collumnating lens assemblies, and special current-limiting drivers. If turning on and off the supply voltage killed them easily, they wouldn't be sold for use as laser pointers or other applications, because they would be virtually useless.

Now, if you were talking about tube lasers or other systems, that would be a different matter.

If you are still concerned about rapid switching, go out and get an el-cheapo pointer from the "dollar store" and hack it; once you have it switchable, hook it up to the Arduino and mod the blink sketch to pulse it rapidly. Leave it running for a day; is it still working? If so, you likely have your answer. If you are still concerned, then get a cheapo green module off of Ebay (one supplier I have used in the past for modules drop-ships out of china, his green 5mw modules run about $25.00 each).

Or - look into people building laser TV projectors - they use a raster scan system (essentially spinning mirrors), and then use special circuitry to vary the brightness level of the laser, which is usually one or more cheap (or not so cheap) laser pointers. Maybe they have a schematic you can use to turn the diode on, off, or anywhere in between.

Good luck!

 smiley
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Richard, I think maybe what the poster is concerned about is doing high-speed switching (or any switching at all) prior to the current limiting circuit for the laser diode (ie, the switch would be in-between the current limiter and the power supply).

If any damage occurred, it would likely be to this circuit, and not to the laser diode itself. I honestly don't know if such damage would occur (I have seen plenty of laser-pointer switchers that just switch the voltage to the current limiter that is presumably inside the laser module), but I can understand the concern, especially when you get into the more expensive laser diode modules (of 100mw and greater); burning something like that out can be painful.

Here's a link to one such simple schematic:

http://laserpointerforums.com/attachments/f42/11702-diy-homemade-laser-diode-driver-ld_driver_schematic.jpg

I don't know if this circuit is correct, if it works, or what - but that is essentially what is in most laser diode modules (it's meant to drive a bare diode, like what you would pull from a blu-ray player or something, I think).

I guess if there were a real concern, you could throw the switch after the LM317 on pin 3, or maybe even before the diode on the positive rail (though I wonder if switching the current on and off rapidly at that point would actually change it enough to harm the diode?).

Hmm...

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Thanks for your comments! Maybe I'm just a anxious and just need to try it ...
christian
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I've switched a 100mW laser diode via arduino before... was making a laser harp...

And, you're somewhat right to be concerned; you likely won't blow anything up, but depending on your driver design, you might have a non-zero turn on time.

The drivers for bigger diodes include feedback and thermal compensation circuitry to prevent you from frying the diode; this will generally keep you from doing bad things to it, but all that circuitry takes power to turn on and off, resulting in a non-zero turn on time.  And it completely prevents you from adding a smoothing cap to the driver power supply, cause that'll change the turn on time from msecs to secs

Some drivers are designed to take a TTL input to switch the diode; in those drivers, all the circuitry is left hot when the laser is off so you get very fast on times.

If you can't find a suitable driver (I bought mine off ebay for $20), Sam's Laser FAQ (Google is your friend) has many reverse engineered driver designs.

And finally, what others have posted is right; your 100mW laser will likely only engrave or burn.  And that's if you focus it really well, on dark colored material.  An adjustable focus rig and patience would be required to cut any appreciable thickness of material.  My advise is to pick up a 1W or higher IR diode on ebay... you can get those for ~$20 without any of the extra stuff you need.  You'll need a lot of extra stuff though, like:

C mount diode housing (preferably with heatsink)

IR-compatible collimating lens (plastic, not glass, people!  glass blocks most IR light)

diode driver (your 100 mW driver won't even cascade the IR diode; it'll light dimly as an IR LED, but it won't lase with that driver)

IR laser safety goggles!!!  The good news is that your eye isn't very good at focussing the IR wavelengths you'll use.  The bad news is that 1W is enough to do plenty of damage anyways, so play it safe.

IR viewing card (rat shack has these for ~$5)

And if you want the ultimate in safety, a glass aquarium to block the IR light (test with the viewing card + safety goggles) - use it as a cutting hood to block any IR reflections.

I can't stress it enough, even looking at the pinpoint of a 100mW laser focussed strongly enough can be blindingly bright, protect yourself!!!
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I may well be wrong on this, but I was not aware that glass is a significant IR block, unless specially coated..

UV, yes....
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thank you merlin _jim for the detailed answer.

I think the turn on time will be a minor problem for my laser cutter project as I can let it wait for as long as needed (without delay would be better though).

What I'm more concerned about is the needed power and wavelength of the laser. I read so many different opinions that I am totally confused. On the one hand, I believe the experienced users who say that at least 1W or even more is needed, on the others there are project reports out there in diverse forums that point in a completely different direction. For example this:
http://laserpointerforums.com/f44/built-xy-table-need-more-firepower-47137.html
and what is to think about this 260mW laser module from ebay, which is described as "good for cutting on hobby CNC". Maybe it is not very good in doing that, but it's far away from 1W
http://cgi.ebay.com/260mw-780nm-infrared-laser-cutter_W0QQitemZ180446582522QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2a037456fa

Some further hints and information would help me very much.

Thank you!
Christian
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