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/diy/ - Do It Yourself

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432987 No.432987 [Reply] [Original]

I want to make that tri laser thing from predator, and I think I got everything I need. But I'm not sure what the best way to run the circuit would be. The lasers are each 3wDC lasers, and I'm thinking of powering it with one 9v battery. Would it be a good idea to run the wires like pic related? Or should I try to have it run in such a way as where the first laser won't get the full 9v?

>> No.433007

Or you could've just bought a laser pointer, a piece of thin plastic, and used the head of a needle that had been heated up to etch the triple-dot pattern into the plastic to get the same results with less risk of destroying everything.

>> No.433012

Do you mean they are 3v dc? 3 watts does not mean 3 volts. Also your setup will work (although 9v batteries are pretty expensive per watt hours) if they all have the same resistance.

>> No.433014
File: 16 KB, 800x446, Predator_38.jpg [View same] [iqdb] [saucenao] [google]
433014

>>433007
that wouldn't work, the three points have to actually be spaced apart.
>>433012
fuck, I always get the watts/volts thing confused. They're 3v lasers; would running the 9v battery the way I'm thinking damage the first/second lasers from getting too much voltage?

>> No.433020

>>433014

You don't understand much of anything, do you?

http://www.ehow.com/how_10072846_make-laser-pointer-beam-heads.html

Exact same method is how laser pointers get all those neat pattern-emitting heads.

The plastic doesn't even have to be black. You could use diffraction grating and do the same thing with a much more specular effect.

>> No.433024
File: 7 KB, 211x251, lol'd.jpg [View same] [iqdb] [saucenao] [google]
433024

>3watt laser
the 9w setup will be fine, but you will need a series resistor. im asuming you will have regular 5mW laserpointers. so a 9v batter will last a long time.

>> No.433027

>>432987

OP, you have the basic idea correct, three 3V things in series running on a 9V battery.

the problem is it probably wont work as you plan, not because your theory is wrong, but because manufacturing tolerances in the laser jobbies will mean that they wont get 3.0V each. one might get 1V, one might get 4V, etc.

if you put three resistors in series like that, and they were all the same resistance, then you are 100% correct, the voltage would divide evenly -- assuming the resistors were the same. the CURRENT through the resistors though is the same -- they are in series.

lasers aren't resistors, and their "resistance" is complex (they are semiconductor electronics...)

with resistors it's plain old Ohm's Law. you should wikipedia it or something, you are very close to understanding it all now.

>> No.433029

>>433027
>the problem is it probably wont work as you plan, not because your theory is wrong, but because manufacturing tolerances in the laser jobbies will mean that they wont get 3.0V each.

What is binning, Alex?

You don't seem to understand semiconductors at all, so your advice should not be taken.

>> No.433035

>>433029

OP is wiring not three laser diodes in series (where the voltage drop would be constant enough) but three LASER POINTERS. In this case it may not work, as i stated.

laser DIODES have a much larger voltage drop. laser POINTERS contain a voltage-boost power supply that turns the 3V battery into a regulated current for the laser DIODE inside it. that active circuitry is what will have the large tolerances, etc, blah blah.

BUT! just fucking try it. the worst it can do is ruin a laser pointer.

signed, electronics geek with 35+ years professional experience.

>> No.433037

>>433035

Laser diodes have the same voltage drop as what's required to make the fucking DIODE light up, since a laser diode is a fucking typical LED in a different package, and before sale, all fucking lasers are BINNED for power output/wavelength output/etc.

Signed, someone that actually manufactures optoelectronic hardware, and works with Cree, Nichia, Epistar, Phillips, and other global optoelectronics manufacturers.

>> No.433067
File: 4 KB, 464x279, diode.gif [View same] [iqdb] [saucenao] [google]
433067

>> No.433065
File: 34 KB, 400x300, diode curve.jpg [View same] [iqdb] [saucenao] [google]
433065

the voltage, current relationship on a diode is not linear. small changes in voltage create large changes in current (forward region on pic). hooking them in series with no resistor will likely make the brightness of them unequal due to slight variations from manufacturing.

best way is to run 1 with a series resistor and then have 3 parallel branches. this isn't the most power efficient though.

If you hook 'em in series, you should use a current limiting resistor.

>> No.433073

>>433065
>If you hook 'em in series, you should use a current limiting resistor.

Praytell then, why do micro-array manufacturers not put in a micro resistor inside their multi-LED packages?

>> No.433516

>>433037
> pointers...

OMG duh 1000 pardons, you are of course correct, red laser bandgap voltage same as LED. i brain-farted bigtime here.

i did, likely incorrectly, assume OP was using laser POINTERS which, imho, wiring in series would be likely/possibly problematical.

but you are drop-dead correct and i was wrong, if DIODES, V is constant.

but of course (also) the required dropping resistor may end up too small to be practical for some (laser, LED, lol) diodes on a 9V battery when you consider battery droop etc.

my apologies for putting bad info in a thread. i actually do know better (which makes it worse, no tbetter)

>> No.433521

>>433516

Sooo.. you're saying Laser Pointers don't use Laser DIODES?

>> No.433564

>>433521

sigh... laser pointers use laser diodes, with whatever bandgap voltage the diode requires... 1.8 - 4 volts etc. but many laser POINTERS use one AAA, one AA, (sometimes a 12V, whatever) and some tiny little boost or buck switcher to suck all the juice out of the battery (constant current output i assume).

SO. wiring *those* in series may be more problematic.

beat me up if you like, tho it doesn't contribute to the thread.

>> No.433586

>>433564

Not beating you up, I just misunderstood what you were saying. It was misleading.

Thanks for clarifying.

>> No.433616

>>433564

Most of the ones using a single battery are using a joule thief to force the LED to light, even under extremely low source voltages.

>> No.433709

>>432987
damn, 3 fucking watts ?