Re: Classic LED displays Message #5 Posted by Andrés C. Rodríguez (Argentina) on 6 Oct 2009, 4:48 p.m., in response to message #4 by Jacques Laporte
Red LEDs forward drop is 1.6 Volt (Plank's constant and the electron charge are related to such voltage drop and the wavelenght of the red light obtained; but that is another story), so you can select your resistor as per
R = [[VCC - 1.6 V]*1000] / I
where
R is the series resistor, in ohms
VCC is the power supply voltage, in volts
I is the desired current, in milliamperes
For VCC = 5 Volt, and I = 10 mA, a 330 Ohm resistor is adequate. Please check with the display spec sheet about a safe current value before starting your tests. Good luck!!
All this assumes a permanent condition, no multiplexing or pulsing of any kind.
|