QRD1114 Optical Detector Hookup Guide
The LED is supplied by 5V with a 330Ω current-limiting resistor. The value of this resistor can be decreased to around 175Ω to increase the LED current closer to 20mA.
The transistor's emitter is grounded, and the collector is connected to the Arduino's A0 pin. The 10kΩ pull-up resistor helps turn the transistor's light-variable current into a light-variable voltage.
Here is an example breadboard wiring diagram for the circuit:
There are many ways to assemble this circuit on a breadboard. The example above straddles both the LED and phototransistor across the breadboard's median.