one led = one resitor, two leds = two resistors and so on?

Hi,

At this point, I know that if I connect one led (5mm), I need to put one resistor (330 Ohm). Now I want to experiement, but I have some doubts.

1-If I put 3 LED's, I need to put 3 resistors? 2-How do I know the resistor that needs to go with a determated led? 3-How many LED's can I light, with the energy that comes from Pin 12 of Arduino Uno?

Cheers! Dani

for single LEDs I use this : http://led.linear1.org/1led.wiz

and for multiples, I use : http://led.linear1.org/led.wiz

hth

1-If I put 3 LED's, I need to put 3 resistors?

YES

2-How do I know the resistor that needs to go with a determated led?

Ohms Law. The Volts, you know... it's 5 Volts. Current is the current you want to allow to flow through the LED, usually around 20mA. After an Ohms Law calculation (R)esistor Ohms =Voltage (E) / Current (I) so you find the closest standard value resistor = 220 Ohms

3-How many LED's can I light, with the energy that comes from Pin 12 of Arduino Uno?

Roughly = 2

Ohms Law. The Volts, you know... it's 5 Volts.

This is an improper application of Ohm's law. Ohm's law applies to the [u]resistor[/u] alone, not to the power source, not to the LED, and not to the resistor/LED combination. The voltage across the resistor is probably not 5v.

Don