This Instructable will show you how to use your Arduino module to detect whether a flashing IR signal is present.
This could be useful in IR tracking, where you don't want to track the brightest IR object but the one pulsing at a certain frequency.
Circuit Layout (refer to Drawing)
Simply connect the Phototransistor and Resistor in series.Connect the emitter pin of the Phototransistor (long leg) to GND and the collector pin (short leg) to the resistor which we will connect to the 5v pin of the Arduino.
Analog pin 0 needs to read the voltage drop across the Phototransistor so connect the A0 pin to the Phototransistor's collector pin.