YMMV

* your mileage may vary

Thursday, 24 April 2014

On LED's

Normal LED's draw about 20mA
Rated between 2-3 volts depending on colour
  • White LED: 3.2V 25mA
  • Blue LED: 3.2V 25mA
  • Green LED: 2.1V 20mA
  • Red LED: 2V 15mA
use ohm's law to figure out what size of resistor to use R=(Va-Vb)/I
where Va = volts of battery, Vb = volts rating of LED
I is in amps (20mA = 0.02 amps)

e.g. Red LED resistor size (minimum)
  • (5volts - 2volts) / 0.02 = 150 ohms

Current flows one way (won't work plugged in wrong)
  • long leg = positive (anode)
  • short leg = negative (cathode)

long leg attaches to red wire (positive side of battery)

remember short wire is less..... and less = negative.
LED also has flat surface on the lens for the negative / cathode side

No comments:

Post a Comment