Modding 650nm for switch + 9v

[Redstar]

I'm working on my first experiment with lasers, and with no background in optics or electronics, i'm getting stumped by the simplest problems.

I've got a little red keychain laser ptr. that I want to power with a 9V battery; also, I want to replace the momentary button on its circuit with a rocker toggle that'll be located roughly 2in. away from the laser module.

The laser was originally powered by 3 AG13 button batteries (1.5Vx3); the switch was located in the circuit before the negative terminal of the battery, and the positive terminal was the metal housing itself. It's a very cheap little Chinese laser, sold as a pet toy. It didn't come with much by way of stats, but here's what I can see:
Class 3R laser product
Max. output 5.0 mW
Wavelength 650nm

Simply contacting the terminal points on the circuit to a 9V battery does nothing; I'm guessing 9V is too overpowered for the diode to activate. What would I need to do to make this work? What other information can I give? I don't need this to do anything amazing; it's meant to be a laser sight for a prop (costume) gun, and is purely for cosmetic effect.

If pics of anything would be useful, I'll be glad to post some. Thanks!

 

[styropyro]

A 9v battery can fry that laser unprotected, you will want a resistor in there. Desolder the switch and resistor off the board, and put a 200 ohm resistor on the positive pin of the laser diode. You can get resistors at RadioShack. You can also get the switch you want there.

 

[photonaholic]

I know your standard 9 volt cell is not quite the king of current output, but those little pointers have no driver circuits in them.

Simply put 3 hearing aid buttons cannot make enough current to harm the diode.

For under 10 bucks you can easily get a small red module with 2 wires ready for your project and it will suit your needs well.

It will be low power, so quite safe.

oh and........

Welcome to LPF. Enjoy your time with us here.

I have included a handy guide to assist you in finding what you need.

 

[Redstar]

Thanks for the quick replies!

@Styropyro: The "board" is really just a tiny bit of silicon with two leads on it; leading out from the diode, there's a small white bit of "something" inline with the lead that fed the "+" end of the old switch; the switch bridged to another line which led to the spring that held the batts in place. I've honestly never seen such a simple circuit; the white thing doesn't look like any resistor I've ever seen, but I'm guessing it does provide resistance somehow.

I'll post a pic tomorrow to better explain.

Also, I've already got a switch; it's a mini rocker toggle. All I need (hopefully) are resistors

@Photonaholic: Might you be able to point me towards something online like the module you're referring to? I'm honestly too new at this to know what I'm looking at when I search for "Laser diode module", and while I'm interested in learning, I'm also impatient to keep moving on the thing I'm building.

Also, I did try to use the search bar (not new to forums in general), but like most forums' Search functions, it didn't turn up anything remotely related to what I was here for. Sorry if this is a dupe of a common thread; I looked and didn't see it.

Thanks again for the help guys.

 

[silvercookie]

buy this.
150MW Red Laser Diode DIY Module - eBay (item 230421226479 end time Feb-06-10 01:42:28 PST)

build a cheap lm317 driver.
http://laserpointerforums.com/f42/diy-homemade-laser-diode-driver-26339.html

then mount it in one of these.
Parts-Express.com: Hammond 1591LSBK ABS Project Box Black | screws screw PROJECTS project box mounting hammond CTS box ac abs

radioshack also has those boxes.

and use these for a power supply.
Card: 2 RCR123A 3.0V 750mAh LiFePO4 Batteries + Charger - eBay (item 330395534617 end time Jan-25-10 00:14:07 PST)

 

[Redstar]

@Silvercookie:
That's definitely helpful; I'll be sure to read over the links thoroughly. Couple questions:

1: Are you saying I ought to forget about using the bits I already have? Sadface.

2: If I use styropyro's 200Ω resistor suggestion, would I be able to substitute a 9V for the power supply instead of those 3.0V buttons? I'm trying to make this thing with parts that are readily and cheaply available; the end goal is to make something that I'll be able to hand to someone and have them know what to do with it.

3: Is there something I can read that'll give an overview of how to pick resistors for a circuit? I've done a bit of reading already, but I've gotten lost on the parts about calculating voltage drops across the diode; doesn't seem like that's something they tell you on a consumer-market laser pointer.

Again, thanks for the advice.

 

[silvercookie]

1. honestly, for all the work you want to do to a cheap 5mw pointer, to me it wouldnt be worth it, when you can build a much bigger laser for not much more $.

2. if you havent already read this, read it.
Resistors
another good calculator.
Ohm's Law Calculators
3. look above. i was looking for a chart with a list of voltage drops from each ohm rating, but couldnt find anything.

 

[Redstar]

Just wanted to follow-up: The 200Ω resistor did the trick perfectly; the laser looks rad and does exactly what I wanted (thanks styropyro). I'll put a few pics up after I finish up.

Thanks again for the help, everybody - much appreciated!

 

[photonaholic]

looking forward to your pictures!!

 

[Greenmechanic]

Redstar, Just a little FYI.
Some of those little cheap pointers can take a lot more then 3V.
I bought 20 of them for $6.00, so I did some torture tests on some of the lower power ones.(ranged from .2-6.8mW stock)
I managed to put 13V into one without it failing, albeit with very short duty cycle (output 23mW)
Most would hold up at 6-9V. I ran one for >1 hour @this voltage, mW actually increased over time.(10mW>14mW) WTF!
Of course, this all depends on the laser's maker and factory spec's. (I'm sure I bought a "freak" batch)