Green Laser Diode/Driver problem/New project! - Page 1
Forum section: electronics / projects

author: obnauticus
author_rank: Newbie
timestamp: February 22, 2010, 02:03:50 am
content: Hey!I just picked up an American DJ Emerald Scan for $40 at a local thrift store. All the robotics work which is very nice. The problem I am having though is either the driver board or the diode is broken. When the driver board from the original device is driving the green 4.9mW laser diode it lases a very faint red. What would cause a green laser to lase at this wavelength and intensity?When I plug an external power supply into the diode, it lases green at 2.0VDC at around 300-400mA. With that in mind I am thinking this is more of a problem to do with the driving circuitry in my new device.If I need to replace the driver/diode, what do you guys think I should throw in there? Keep in mind the application of the device...I dont want to burn people's retina's out while dancing with a 500mW laser lol.In the event that someone else finds these handy, attached are pictures of the internal design. It is very modular which is nice.http://img186.imageshack.us/i/img00168201002201738.jpg/http://img522.imageshack.us/i/img00167201002201738.jpg/Here is a full PDF manual for the device:http://www.blacklight.com/files/ADJEMERALDSCAN.pdfWhen I hooked the Positive and negative leads of the driver into my scope I saw the following image (the top one is +, and the bottome one is -, because of the refresh rate of my camera, the lines look like they are going stright through the pulse cycles, but they dont in the actual graph). The duity cycle pulse is to control the dot size, and it reacts in height and width to bass.Here is a video:http://yfrog.us/1svid00014201002211728zThis video is better, you can see the pulse width and duity cycle of the pulse changing as I blow into the device's embedded microphone. I still do not understand why there is an AC looking waveform going into this diode.http://yfrog.us/09vid00015201002211734zThanks in advance!obnauticus

author: aXit
author_rank: Contributor
timestamp: February 22, 2010, 11:18:06 am
content: Please please please don't look into that faint red light.Green lasers that are used in devices today are never just a green diode (unless you're paying >$5k). They use a system called DPSS, diode pumped solid state; what this means is that there's a high power infrared diode in there lasing at 808nm that "pumps" or stimulates other crystals in the module that eventually, through a complex process of re-emission of light and frequency doubling, comes out at 532nm, which we see as a nice emerald green.What's happened is that those crystals have come out of alignment (in any axis, even rotation will stop any emission of light) and you're looking into the pump diode.I'm sorry to say, there's nothing you can do for the module now, there's no way to realign the crystals.I'm not understanding what you're talking about with the actual signal going into the module, but I'll just say it'll be difficult to make it work with any replacement module you buy, unless it's from the manufacturer (but they'll charge you a ridiculous price). Modules that can be purchased generally use a simple switcher; which don't respond well to the AC input signals you're referring to.Good luck with it! Sorry I can't help much with the electronics, but feel free to ask anymore laser related questions.aXit.

author: rossmoffett
author_rank: Regular Contributor
timestamp: February 22, 2010, 02:19:04 pm
content: On that note, 5 mW green laser pointers on eBay are only $10 or so. The modules can be peeled right out of the head and the cheap driver de-soldered (or used, if you would want to).The reason it's pulling so much current is because as said above, it's an IR laser, the process of converting it is very power-hungry so the IR laser is actually a few hundred mW. There should be an IR filter on it after the doubler though.

author: obnauticus
author_rank: Newbie
timestamp: February 23, 2010, 05:18:17 am
content: Quote from: aXit on February 22, 2010, 11:18:06 amI said previously the diode lases green when I use an external power supply, so it must be something to do with the driver board, and/or the diode combination.QuoteThat would explain the IR lol, the driver is probably not supplying enough current. I will try to measure the max draw that the driver board capible of and cross-reference that with what it was drawing when an external PS was used when it was working.In the event that both the diode/driver have failed, what is the best solution that i can throw in there (note the diode must be switched on and off really fast, it's duity cycle is consistantly changed). Could I just hook the PWM line up to the signal lead of a FET and the drain to ground so an integrated diode/driver combo would be able to be controlled via a PWM line? It looks like the frequency the laser is being pulsed at is anywhere between 22-60Hz...

author: aXit
author_rank: Contributor
timestamp: February 23, 2010, 08:40:21 am
content: Sorry, missed that little bit of information.It's definitely an issue with the power supply then, specifically, not outputting enough current.The crystals inside have a lasing threshold, a minimum amount of light that must be passed to start working.On a side note, 300-400mA is a lot for a 5mW module, my couple of 50mW modules that I tested just then draw around 290mA each, and a 150mW one I have draws 650mA. It may be a little overspec.

author: rossmoffett
author_rank: Regular Contributor
timestamp: February 23, 2010, 07:53:24 pm
content: I think the higher wattage green lasers have better crystals, not necessarily more power on the IR laser.

author: obnauticus
author_rank: Newbie
timestamp: February 24, 2010, 03:17:03 am
content: I just measured the input power on the driver board. It's getting 28~29VAC on the input, and its not being rectified at all before sent to the laser. This explains why the laser is not lasing.....the signal line for the laser pulsing also seems to have a 28VDC wave superimposed on it. This is weird...maybe a floating ground or something....the board does not look like an AC board at all lol.