I have this homemade LED-USB thingy to illuminate my desk:
I guess it's not a very technical schematics, sorry, I'm not even near the EE area. The LED is 3V, and according "to the internet" (there was no manufactorer info on it) a blue LED usually supports up to 0.03A.
Thing is, it's not bright enough, so I want to attach more LEDs to it.
Since I have spare current from the USB I thought I should build a parallel circuit. Now, the last class on circuits I had was on high school, so I don't know if my calculations and schematics are correct:
i_total = U_wanted ( 1/r + 1/r' + 1/r'' ), r=r'=r'' i_total = U_wanted ( 3/r ) 0.5A = 3V ( 3/r ) 0.5A = 9V / r r = 18 Ohms
Is this correct? If so, what material should I use as wire? A copper wire? Also, is it safe to touch it while it's on? I've been avoiding it, but I guess it's a low current and voltage...