I have my arduino working to control a Lego IR receiver. Unfortunately it only works if the receiver is very close (<5 cm) to the IR diode I'm using. I just connected the IR diode to pin 13 and added a 330 Ohm resistor. I also tried with ~165 Ohm, but didn't get a better result.
How can I make the arduino sending a a much stronger IR signal so I can control a lego car in our living room? This means it has to send an IR signal which reaches the receiver within some meters.
The lowest value I used for this resistor is 100 ohm. If the result are not satisfactory add a transistor and several ir leds in parallel.
Another approach is to look for IR leds with more focus.