njs707:
VCC ____ - Receiver + _____ A0 pin __________________
|
- _____ 10k ohm ____ ground ______|
Don't connect A0 to Ground. The diagram is a bit confusing because it uses the same type of line to show the edge of the Arduino and the connections TO the Arduino. The resistor and Arduino are connected to a common ground. The A0 input is only connected to the junction between the phototransistor emitter and the load resistor.
njs707:
http://www.instructables.com/image/F4M09OIF6S98GAG/IR-Detector-Circuit.jpg
That example uses a digital input with the internal pull-up resistor enabled. Current through the phototransistor drags the signal down enough to register as a 0. The analog inputs don't have the option of internal pull-up resistors (as far as I know) so you need to provide the +5v source. Current through the phototransistor and resistor raises the voltage across the resistor and this voltage is measured by A0.