Construct IR Light Source:
On a breadboards, hook up an IR LED to provide an infrared light source for signaling the phototransistor as shown in Figure 2 below. Use a pushbutton switch to turn the IR LED on and off. Note that the pushbutton does not require any resistors to ground as it only needs to control when the power enters the power rails on your protoboard. The IR LED will drop approximately 1.35 volts and should be operated with ~100 mA of current.
Calculate the value required for the resistor labeled R in the circuit below to achieve these design specifications.
Now calculate the power that you expect this resistor to absorb (remember the formulas for power in terms of current and resistance)