Pyro Propeller Clock POV

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IR Home Sensor Theory
           To make this system more fault tolerant, a 'home' location is built to tell the system when it has reached 0° and to restart outputting the image. The circuitry used to build this home sensor are the IR emitter diode and Phototransistor.

Intro To The IR Emitter/Detector Pair

           The video above illustrates how you can use a simple circuit (shown below) to detect if an IR Emitter Diode is present or not. When the IR emitter led is turned on, the phototransistors detects the IR light and switches the red LED (in the video) off. This simple idea will be used in the propeller clock to let us know when the propeller has passed over the 'home' location.

Propeller Clock IR Home

           The picture seen above shows you where the 'home' location actually is on the pyro propeller clock pov. Whenever the propeller passes over the IR emitter, the phototransistor is turned on, connecting the 'collector' +5v pin to the 'emitter' ground. The PIC sees this 'falling' edge transition and knows that home was just reached.