Repurposing unknown low power laser - Page 1
Forum section: electronics / beginners

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: October 25, 2021, 07:03:51 pm
content: Hello everyone!I’m trying to get an old laser diode working but I’m not sure how. The laser diode comes from an old 3D-printer (Davinci Pro), I got some parts of it when it was scrapped. I did not get the main board.The laser is specified for 350mW and has 4 leads coming of it. I’ve not been able to find any info about the laser.The leads seem to come in pairs, one diode between each lead pair. I assume that one is the laser diode and the other is for temperature measurement, maybe?I’m not sure how I’m supposed to verify this without destroying the laser, I don’t own a low power constant current driver and I don’t want to accidentally destroy a temp sensor.Below are some measurements and images of the device.Side note.I’m planning on using this to cut PCB stencils out of thin plastic films like Kapton. I know that the printer originally came with Kapton film for this type of use but never tried it myself.So the second question would be if anybody knows of a cheap alternative to Kapton film, I don’t want to buy a huge roll of it nor do I want a tape.Thanks for any suggestions!

author: magic
author_rank: Super Contributor
timestamp: October 25, 2021, 07:32:36 pm
content: The other should be a photodiode for optical feedback.Here's a laser pointer drive circuit I reverse engineered once.https://www.eevblog.com/forum/chat/is-there-a-simple-circuit-solution-for-this/msg3623698/#msg3623698I don't know how to safely drive higher power diodes, but the tiny ones like above often are as simple as a "current source" consisting of a resistor and a 5V supply specificationBut IIRC, the purpose of optical feedback is to prevent damage to the internal mirrors which may happen in some diodes even if their thermal rating is not exceeded(?) So it may be wise to abstain from random experimentation. Ideally, you would find more information about the original driver circuit.

author: antenna
author_rank: Frequent Contributor
timestamp: October 25, 2021, 07:41:35 pm
content: Could you post up close pictures of both sides of the board it was connected to? Here is one from a supplier but it is not clear enough. The board may offer some clues.

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: October 25, 2021, 07:56:22 pm
content: Thanks for the tip magic, il look into it!If I remember correctly, the was just straight tracks from the laser to the other connector. The only thing of interest was a EEPROM that contained the serial number and type of module. Might dump the memory if I get the time!R1 is 0 ohms.Below are the PCB images.

author: james_s
author_rank: Super Contributor
timestamp: October 25, 2021, 09:35:52 pm
content: I certainly wouldn't consider 350mW to be a "low power" laser. That's a class III-b, only a bit under the threshold for class IV which is the highest the categorization goes. It's not going to vaporize your finger, but it is certainly capable of causing eye damage very quickly.

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: October 26, 2021, 02:04:45 pm
content: Your probably right James, I’m not too experienced when it comes to lasers and the only other lasers, I’ve used are +100W CO2 lasers that can cut through thick wood like a hot knife through butter.I’ve managed to get a hold of an original main board for same printer, I’ve attached the images in this post. The image below is what I presume to be the area of interest. Images are attached.Guess I have to start revers engineer the circuit...

author: Terry Bites
author_rank: Super Contributor
timestamp: October 26, 2021, 04:09:08 pm
content: Any laser that can cut is not in the low power category. If it can cut Kapton it can blind you. If its IR its even more dangerous becase you wont see any visible light or stray reflections.The LD needs a contant current drive. The PD sense provide feedback to keep the diode ouput from possible thermal runaway. See this post. You dont have to modulate it of course.https://www.eevblog.com/forum/projects/laser-diode-driver-khz-modulation-1-duty-cycles/

author: ejeffrey
author_rank: Super Contributor
timestamp: October 26, 2021, 09:17:31 pm
content: My guess is that the .570 V diode is a silicon monitor photodiode. The .265 V is probably a shottky diode being used as reverse protection for the laser diode which appears to be a 405 nm blue laser diode. Likely your diode measurement meter doesn't have a high enough output voltage to reach the turn on threshold. The operating voltage of blue lasers is usually just under 5V.That laser is no joke and it is capable of causing instant eye damage, potentially even from scattered light. Even light generated when operating well below operating current, such as when using a diode tester can be dangerous. If you are going to play around with lasers you should invest in a pair of laser safety glasses designed for the wavelength you are using.Experience with a CO2 laser doesn't necessarily translate. CO2 lasers, while often incredibly powerful, cannot penetrate the cornea and thus are not focused onto your retina. They can still cause eye damage through burning especially given the high power, but they are just different animals than NIR/VIS/UV lasers. In addition, playing with a bare laser diode module is different than dealing with a tool like a laser cutter that is hopefully built with safety in mind and has interlocks or shrouding to reduce the chances of accidental exposure.

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: October 30, 2021, 05:27:20 pm
content: I just wanted to thank you all for the great replies. Especially emphasizing the danger with these types of lasers!Il order a pair of laser protection glasses, I also obtained the side panels for the 3D-rinter/laser and will build a box of them. The panels are made of some type of soft/flexible dark plastic, I assume that it will block out most harmful light? Can I verify this somehow?Quote from: ejeffrey on October 26, 2021, 09:17:31 pmI just want to make sure I understand what you guys mean regarding the internal configuration of the laser. The schematic below is my understanding of it.Thanks for all the great info!The glasses I’m considering.https://www.amazon.com/MCWlaser-Protective-190-2000nm-Rejuvenation-Pigmentatioin/dp/B07XKRCD11/ref=sr_1_5?crid=3NOV2L8DLQSH9&dchild=1&keywords=MCWlaser+IPL+Laser+Safety+Glasses+190nm-2000nm+Eye&qid=1635614154&sprefix=mcwlaser+ipl+laser+safety+glasses+190nm-2000nm+eye%2Caps%2C128&sr=8-5

author: ejeffrey
author_rank: Super Contributor
timestamp: October 30, 2021, 05:42:57 pm
content: Yes your schematic is what I think is happening.I don't think those laser goggles are good for two reasons. First they are listed from 190-2000 nm. If that was true they would be opaque! Proper laser glasses should list the specific wavelengths they are good for.In addition this information should be printed on the glasses themselves so that someone picking them up knows what protection they offer. For instance you might have multiple sets for different lasers, even if they look the same you want to know at a glance without referring to a data sheet what they do.The second reason is they say they should be discarded if the film is scratched. This implies a coating based filter. Proper laser safety glasses have the filter material embedded into the plastic material so that scratches do not compromise their performance.

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: October 30, 2021, 05:52:12 pm
content: Thanks for the lookout!Il get to work on the driving circuit and post it in the thread as soon as I think I’m done with it. Mostly just adapt the other recommended designs.Do you have a budget friendly recommendation for some laser eye-protection? As long as it protects against the emit wavelength I’m fine. Doesn’t have to be such a wide range.

author: james_s
author_rank: Super Contributor
timestamp: October 30, 2021, 06:16:18 pm
content: I don't have a specific recommendation, but check the wavelength of the laser you have and look for some safety glasses intended for that specific wavelength. Assuming this is a 405nm laser the correct glasses will likely appear yellow-orange.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 30, 2021, 08:45:06 pm
content: I have only used them in commerical / educational settings and we got the expensive ones from thorlabs. Therefore I am very hesitant to recommend a specific inexpensive model from Amazon or similar. But when I look on Amazon there are a lot of yellow orange glasses that say from 190-450nm which is reasonable. I would test whatever you get.

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: November 02, 2021, 03:50:01 pm
content: I came up with this circuit. It’s mostly just a simplification and adaptation of a Maxim appnote (AN1811)https://pdfserv.maximintegrated.com/en/an/AN1811.pdf.Not sure if it’s the best design but tried to use as many components that I have laying around at home.This should result in a diode current of ~72mA @ 5.0V = 360mW and the diode is rated for 385mW.What’s your guys thoughts?