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i have a laser diode that needs between 3.7v  and 4.2v to run,
http://www.laserlands.net/gd-ms-200mw-green.html
and i plan to run it of an arduino (5v).
to reduse the voltage i have calculated that i need a resistance of aproximately 1.333ohm. is this necessary/is there a bether way to do this?

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## 3 Replies

iceng (author)2014-09-15

Trying to run a laser on voltage says you are a beginner.

PLEASE Take great care, green lasers are actually powerful 808 IR lasers about 20x http://en.wikipedia.org/wiki/Laser_pointer#Green

So if your green laser is really a 200mw green a Very Dangerous laser,

The IR section power is in the 4_Watts range. P = 4.2 x .750 = 3.15 Watts

steveastrouk (author)2014-09-15

The data sheet says it needs a current of <750mA.

Laser diodes, like LEDs need a constant CURRENT driver, so I'd use an LM317. It won't run off an Arduino directly.

Here's a circuit that will work - in this one, the constant current is adjustable. If you want a fixed current, omit the two vertical resistors and connect the ADJ pin to the "current" terminal at the right.

mpilchfamily (author)2014-09-15

Resistors reduce current not voltage. A resistor won't do. Just put i diode in series between the laser and the power. If the voltage drop of the diode is .5V then put 2 in series and you'll have the 4V needed to run the laser. Though i doubt the .8V overage the Arduino provides will affect the laser at all.