# Serious Radio Shack/New Wish green laser discussion



## monel_funkawitz (Feb 18, 2008)

I have been doing alot of work with the Radio Shack green laser pointer. Before anyone starts chanting "Get a better laser", this is unfortunately all I have to work with. My experience with greenies is limited, but I have a decent amount of experience with reds.

I have been trying to see what this laser will really do. I am on laser #4 right now. Apparently, there are atleast two revisions of the driver on this laser. My first one was solely transistor based, but the currently available ones now have a LA6358NT op amp chip also.

The one I have right now has the external PD disabled. I am running 3.0vdc and 280mw into the driver, and I don't know what that equates to mw out. I have no way to check optical power. With the manufacturers being afraid of lawsuits, I'm sure there are lots of protective measures built in.

First one is the external photo diode, which I removed. The APC has a pot, but it is only variable to within a very limited range. With the external PD removed, the laser sees it as dark and goes to the second stage of limiting. I tried shorting out the 1R0 resistor that is in series with the LD on one of these, and either I got heavy handed or the LD could not take it, and it . Turned into a really weak red LED with no infared out.

This being my last attempt at this, I tried feeding the LD direct and I chickened out before I pushed any real power. I have a bunch of unresolved questions so far, and no way to find the answers.

Does anyone know what LD is in these? What it is able to push?
What is the drive requirements for a LD of this type?
What is the simplest and safest way to drive a LD of this type? (Schematics for a good driver would be great)
I'm sure if it was easily possible, it would be done already. I just wanna know what the hard data is, and not guesses and conjecture.


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## monel_funkawitz (Feb 22, 2008)

Well, with 51 views and no replies, either there is zero information out there, or everyone knows this is a lost cause. 

I am officially giving up on the Radio Shack green pointer. Here is everything that I know to date.

My last laser, I changed out the resistor that is in line with the laser diode (1 ohm) and changed it to a zero ohm surface mount jumper. With the solder, it was reading around .16 ohm through my Fluke. On fresh alkaline batteries, the beam was MUCH brighter. Definately visable in day light, REALLY visable at night. It would smoke paper with black sharpie, and would sting the skin after a few seconds, especially if focused down.

Problem was it would only stay in high power for 3 seconds, go progressively dimmer, then go into TEM1 after 6 or 7 seconds total. Let it cool for a bit, and the process would repeat. It would always mode shift.

After playing around a bit, I hooked it up to my power supply to see what it was pulling, I set the voltage to the driver at 3 volts, turned it on, hit the switch, and it lasted for a second at really high power, blinked a few times, then died. Apparently, the batteries were not supplying it at a full 3 volts under load. (Obiviously)

I disected the pointer, and found some interesting things.

In my first post, I stated that I had a green pointer that was bought when Radio Shack first carried them. In comparing this current pointer to the first one, there are some differences besides the drivers.

The KTP is over 200% larger, area wise, than the first one, and is nested in the mount so more copper touches the KTP than the first one. The first pointer had the KTP mounted in the corner, and more epoxy holding it. The mount where the laser diode sits is also different (New one is longer). This leads me to believe the manufacturer now uses the same assembly for the higher power pointers, and just changes the diodes. The Radio Shack lasers use a diode that must be rated lower than the higher power pointers. This explains the mode hopping and the changes in the laser body itself.

In short, the final verdict on this laser is some of them can be tweaked to put a little higher power, but they are unstable and appear to run lower power laser diodes. The pointer, although it feels hefty, is hard to work on. I have found a way to open them without leaving any tell tale marks, but it is not easy. The only good parts are the laser assembly itself. With a diode change, it would be decent. However, going this far, there are MUCH better choices of pointers to play with.

If anyone has any questions about these pointers, feel free to ask. I know this pointer inside and out. It was a fun project, but I'm getting ready to get something new to play with (Probably one of the cheaper DX lasers)


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## IgorT (Feb 24, 2008)

What power are these lasers supposed to have? 5mW?

If it has a photodiode, the current is most likely regulated from the feedback of the PD, to keep the output constant...

In this case, to increase the output you would have to fiddle with that part of the circuit.

But if you want to test how far you can push it, you should use the LM317 driver in current regulation mode, connect the laser to it, and slowly increase the current, starting somewhere below where it usually is and slowly increasing till you get the output you want or it dies (the latter being more likely)... BTW, in this case you simply leave the PD disconnected.

What are you trying to achieve anyway?


If you want a cheap green laser with a visible beam, you should go with a DealExtreme or a Kaidomain laser.

I just ordered the Kaidomain 50mW for $26 and hope it comes here soon.


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## IgorT (Feb 24, 2008)

monel_funkawitz said:


> After playing around a bit, I hooked it up to my power supply to see what it was pulling, I set the voltage to the driver at 3 volts, turned it on, hit the switch, and it lasted for a second at really high power, blinked a few times, then died. Apparently, the batteries were not supplying it at a full 3 volts under load. (Obiviously)


 
A PSU carries additional risks.. Did you limit the current on it at all, or did you just set it to 3V? Did you hook it up directly or did you hook up the driver to the PSU?

A battery has it's own internal resistance, which limits how much current it can give out, while the PSU is capable of supplying much more.


I killed many red LDs and two Blue Rays by hooking them up to my PSU, even when i used current limiting to a safe level and a capacitor directly on the LD..

The problem is, that the power supply provides a path to the ground for electro static discharge..
In one case this killed a LD even tho the PSU was only powering the driver circuit, and wasn't directly on the LD.


It's actually impresive, that you got it to burn stuff or sting your skin, but it makes sense this wouldn't last long...

Some very low 5mW power pointers can be pulse driven with 500mA and survive for a long time, if the duty cycle is very short.

But as i said before, for a green, that will have a visible beam and won't only last 3 seconds, you should really get a DX or Kaidomain model..


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## monel_funkawitz (Feb 24, 2008)

I just basically wanted to see, for sure, what one of these will do. There is alot of speculation out there, and a million laser new people asking "How can I convert this to burn things?"

My PS was set to 3 volt, and 3 amp, going into the driver. It is an adjustable power supply, and reads current draw. I figured I was safe, with the alkalines pushing 3 volt, but apparently that few tenths of a volt and the ability to feed it however much current it wanted was what killed it. It was a fully adjustable power supply, current and voltage. Being the fact that the laser would TEM01, that tells me that I was at the limit of it already.

My next laser is gonna be a DX, but now I won't have the ability to return it so easily if it dies. My PS is a really high grade one, and is floating. (IE has no path to ground) It is 100% ESD safe, and I was working in an ESD safe lab anyway. It wasn't an issue of static that killed it, but more of the fact of trying to make it do what it just can't. The laser diode itself is the weak part of this laser in trying to make it more interesting to play with. :devil:

I got my funds ready to get a DX. Now the question is which one to get? I hear quality problems with the 200. Which is the most powerful, long lasting one they have?


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