I just found this post on Make. I knew Google could do basic math
but it never occured to me to do anything like this guy, Bob is doing:
Say I have an LED that I want to run from a 12v DC power supply. I
already know that the LED requires a forward voltage of 2v and and a
forward current of 20 milliamps. What I want to know is how big does
my current limiting resistor need to be?
I know I need to drop the voltage by 10 volts, and my draw will be
20 milliamps so I go to the google search page and type "10 volts /
20 milliamps" in the search box hit enter and out pops my answer...
"(10 volts) / (20 milliamperes) = 500 ohms". Woohoo! Now, I've never
seen a 500 ohm resistor, so I opt to use a 470ohm which is pretty
close.
Next I want to build an enclosure for my little project, but I only
have measurements in inches, and I want mm (because I'm an engineer
:P ). This time I type "9 in in mm" and get "9 in = 228.6
millimeters". Great!
Here's a link to the post:
http://www.makezine.com/blog/archive/2007/01/google_calculat.html
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