hey, i have been playing with my arduinos for a while and i’ve never used a resistor for my leds, do u use always resistors when u have a led as output? 220ohm will be ok? and should i use resistors for other things like servo motor?lcd?ir sensor?all outputs and inputs? i’m very confused, sorry for this noob question…

With LED’s the resistor is used to limit the amount of current running through the LED, without a resistor the LED will probably burn out at some time, depending on the voltage . When powered from the Arduino board the LED gets 5 Volts. If you tried running the LED from a 9V battery without a resistor it would burn out very fast.

Here’s a link to a PDf document explaining how to calculate the value of the resistor you should use with your LED’s

For the rest of your question, about using resistors with other devices / components. It can’t really be answered in generel terms. The best thing you can do is to follow schematics that is known to work.

:smiley: thanks for ur reply, i had the basic idea of resistors, i’ll use 300ohm resistor for the LEDs, the other hardware is a sharp ir sensor GP2D12 and the servo motor is a hitec HS-322HD, it works perfectly without the resistors, but ’ don’t know if i should put a resistor or not, i saw somewhere on the web that they used a 10k for the ir sensor, but isn’t that a bit to high? thanks again

If the 10K resistor is for the IR LEd in the sensor it sounds a little big to me.

I found this site to be helpful with calculating what resistor value to use.

The same site has a calculator for driving multiple LEDs.