Old thread, mods please delete!
jimdt7: I have bought 12 high-power leds and want them to be powered via the arduino. Each of these leds needs 3V and 20mA so total i need 36V and 240mA. What can i do ??? Wil i burn my arduino if i connect them ???
Do you mean 12 leds connected in series? Or 12 leds connected in parallel? You almost certainly need to power them with a separate transistor. The base of the transistor (or gate of the MOSFET) will be connected to a digital output of the Arduino.
There are lots of circuits and advice about doing this. Here is one example, see the diagram which says FETSWITCH and TRANSWITCH, these get connected to your output pin:
So your tiny Arduino pin wiggles weakly, but the MOSFET or transistor wiggles powerfully.
These are not high power LEDs if they only take 20mA. You need a resistor to limit the current say 150R and then you can feed them with 5v. To safely power all of these at the same time you need a transistor or transistors. However you haven't communicated exactly what you want to do with these. Is it on off all together, on off separately, or do you what to be able to dim them?