More details and files on my website
Step 1: Make it!
Now for the transmitter part, you will have to connect the collector pin of the npn transistor to the 5v rail , the base to the digital pin 3 and the emitter to the anode (+) pin of the LED. The cathode will be attached to GND trough a 1k resistor.
*Note:If you're in Europe, you'l have to connect the digital pin 5 to ground trough a 1k ohm resistor.
Your breadboard should look like this now: