Laser diodes and drivers.

[GoForSmoke]

I got a few cheap laser diodes that use 4.5V @ 20 mA according to less than datasheet info.

Model   6972
Quantity   10
Color   Black
Material   Plastic + iron
Specification   Power: 5mW; Working voltage: 4.5V; Working current: 20mA; Working range: 1000 meters; Color BIN; Red
Features   Mini and compact design
Application   For DIY project
Packing List   10 x Laser module (8cm-cable)

From what I read, I should use a constant current source and wonder if I really have to give them 20 mA and if not then could use a heat sink to keep the diode in a certain range and reduced power (I don't need any 1000 meters) to have enough margin. Given some equilibrium can be reached without pushing a limit, can it work?

[Nick Gammon]

... according to less than datasheet info.

What is a "less than datasheet"?

[GoForSmoke]

That quoted info I gave is less than a datasheet, LOL!
It's all I've got, the little bit that the HK store (deal extreme) put on the sales page.

A quick look for a datasheet got loads of 'matches' that didn't match.
But please don't spend time looking, they were $4.60 for 10, at minimum wage that's a 30 minute search so please don't bother as they will work in general fashion or they won't. There is nothing hanging on these.

Mostly I just want a clue or so on the care and feeding of cheap laser diodes.

Here's a link. Maybe someone else wants some as that's the most good it might do.
http://dx.com/p/12mm-5mw-red-laser-diode-modules-black-dc-4-5v-165078

If I get them working, I have a cheap controllable source of coherent light. I was thinking, time to buy holograms. Making them requires a solid base and more trouble than I want to go to but to see or possibly project them isn't so finicky.

[GoForSmoke]

HOY! Look what I found!

DIY: Make a $3 Laser Diode Driver!
https://www.youtube.com/watch?v=2Rjlf7gnXms

Best part is I have LM317 **somewhere here** and prolly the rest too!

Added: why I need a driver:
https://www.youtube.com/watch?v=eF1dSMcfteo

[terryking228]

I have a few small Laser diodes that work fine from an Arduino output. They have a series resistor. That's all.

The resistor value depends on the diode. If you use the example you had above:
Working voltage: 4.5V; Working current: 20mA;

And if Arduino puts out about 5.0V for a HIGH (close), the resistor needs to drop 0.5V. So:

5.0 - 4.5 = 0.5   R=E/I  R= 0.5 / .02 = 25 ohms.  

I think the little "Electronic Bricks" I have that plug into Arduino have about 50 ohms. I'll check.

If the current is too low, the laser will not output light, until it receives some "Threshold" current.  You can start with 100 ohms and decrease it and go a little lower than when the laser starts "to lase"...

I have a student making a Cat Toy using one of these with two small servos to dance it across the living room carpet...  

I have to build one of these for my daughter's cats. They love to chase the human-driven laser pointer...  I should have some timing stuff, and a motion sensor to activate it when a cat walks by and no-one is home.  A minute or two seems to be cat-attention-span. Your variables may vary.

[GoForSmoke]

Hi Terry, saw your deal on opto-isolators and passed the link to a friend who needs some.
You beat 20 for $4.40 with 5 for $1.00 so you topped the list.

Working voltage: 4.5V; Working current: 20mA;

And if Arduino puts out about 5.0V for a HIGH (close), the resistor needs to drop 0.5V. So:

5.0 - 4.5 = 0.5   R=E/I  R= 0.5 / .02 = 25 ohms. 

I get a bit antsy about the way you just did that because I used to do that for leds years ago. I'd get a usable value, just a few times higher than it should have been because I didn't take the drop across the led into consideration. I only know some basic, I have to look -everything- else up and wonder what I missed!

So I wonder, is there not much drop across the laser ... enough to make much difference? Not that I argue since HEY you've got the suckers working and very obviously know your EE stuff!

What I'm really looking for is explanation which you and others do provide so I do Thank You For That Given Already. Really... THANKS!

I guess a trim pot will carry a few mA current to let me find out working values. I might want to try resistance for 3V and 6V since I have a load of CR2032's (pretty sure they're 3V) just getting older every day now. They ran me like 25 cents each, just hate to see them go to waste. You'd pick a quarter up off the sidewalk, if it looked clean, wouldn't you? I do.

I gotta see if 2 mW is bright enough to do the 2 speakers with mirrors light show. Well, in a real dark room on a white wall it might.

[terryking228]

I used to do that for leds years ago

This is the same situation as LEDS..

LEDs have drops of maybe 1.2 to 2.5 volts (depending on color etc)

The Laser Diode you have says it has a drop of 4.5V 

The calculation process is the same.  The resistor has to drop (Supply voltage - Diode Voltage) The resistor value is
(Supply Voltage - Diode Voltage) / Diode current you want. 

[GoForSmoke]

IWorking voltage: 4.5V; Working current: 20mA;

And if Arduino puts out about 5.0V for a HIGH (close), the resistor needs to drop 0.5V. So:

5.0 - 4.5 = 0.5   R=E/I  R= 0.5 / .02 = 25 ohms.  

The calculation process is the same.  The resistor has to drop (Supply voltage - Diode Voltage) The resistor value is
(Supply Voltage - Diode Voltage) / Diode current you want. 

Right. My head wasn't working was it? I quoted you showing what I said you didn't. D'OH!
I have no defense except for stupidity! I was just through watching History Channel video, I should know that my brain stops after 30 minutes of that.

We need a bowing down emoticon here.....

[123Splat]

Smoke,
I believe that what you have are not 'diodes', but modules (they already have drivers built in).  you should be able to hook them up to a source that is at, or above, the 4.5V and they will work just fine.

[GoForSmoke]

Smoke,
I believe that what you have are not 'diodes', but modules (they already have drivers built in).  you should be able to hook them up to a source that is at, or above, the 4.5V and they will work just fine.

I went and pulled one out of the bag and you know, I think you're right! There are indeed little boards at the back with thin leads soldered on that look like they'd fall off with a hard shake.

I will still need to use at least a voltage divider if UNO-powered.

[dc42]

It looks to me that they are modules with an internal controller, in which case running them on 5V should be OK.

[GoForSmoke]

Well, I got 10 and they were only 45 cents ea....

Yup, it works, at least for a couple minute test.
LOL it's my first Arduino project that used no programming whatsoever, just plugged the wires into 5V and GND though I had to hold them in.

I gotta see about lifetime at 5V just in case. I did see one youtube video where a guy cooked a component on a pointer that could not light a match and then it did light the match. Short video so I dunno how long that stayed working. But maybe the things are choked for legal reasons and can take it, the pen was a green laser if that makes any difference.

This one makes a real bright dot, nice bright lines when swinging around on the wall. Time to set up a light show box; ie 2 speakers with reflectors playing music unless... ehhh I don't think that piezos will move enough to get a decent spread at 4 to 8 ft but I can try.

The link is in the first post for anyone who wants some. 10 modules for $4.60. DX ships free if you can wait. I wonder if I want more of these before it changes? Light is nice but some time I'd like to cut paper, etc.

[GoForSmoke]

Just a thought... should these be able to switch on and off fast enough to make a raster on a wall?

[123Splat]

Smoke,
Yes on the switching time. 
No,NO,NNNNOOOOO on the trying to raise the power. the process is called 'Pot Modding' and is 1) sure to reduce the life span of the LASER diode, 2) frowned upon by serious laserist (because of '1', and...). when done it usually pushes the diode beyond max specifications.  The greens are DPSS, using an I.R pump diode and very little to no I.R. filtering. A DPSS green producint 5 mW of green light can have up to a 1 W I.R. pump. Not safe to begin with, worse when overdriven.

You will be able to produce some fun effects in a darkened room with what you got.  Have fun, be safe!

[GoForSmoke]

You know the spinning led POV displays? With moving mirrors the laser should be able to do text.
Instead of an LCD, that and a wall or paper or hand....