I'm trying to connect LEDs to pins 13,12 and 11. The LED in 13 works fine, but the other two are too dim to be clearly seen. I understand that pin 13 has a resistor built in whereas the others don't but whether or not I attach a 2.2ohm resistor to 12 and 11 makes no difference to the luminosity. Where am I going wrong?
Have you set the pins to be digital outputs in your code?
Do the Arduinos have a resistor to pins 13? My Diecimila doesn't.
In any case, 2.2ohm resistors are too small for this application, though you will probably get away with it.
220ohm or higher is q more likely value.
To calculate the resistor value required, you need to know the voltage across the LED when powered. It varies for different colours and types of LED. Lets assume it is 1.5V.
Lets say we want to put about 20mA through it and the Arduino is powered from 5V.
We work out:
R = V / I -> (5-1.5)/0.02 = 175 Ohms.
the closest standard value is 180R.
Regards,
Mike
Hej,
Big Mike is right. I just wanted to add, that resistors will not make your LEDs brighter but dimmer. So you probably activated the internal resistors, by not setting the pins as outputs.
Concerning resistors on pin 13. the original arduino and NGs have them. I think the idea was to be able to just hook an LED to that pin for debugging convenience .
//kuk
Thanks for your help