Flash Sensor

A very simple flash sensor circuit was used to detect a flash at the start of the game. An input capture was implemented in software to avoid using blocking code at the start of the game. The input capture was disabled after the flash had been detected so that any subsequent camera flashes would not trigger as a flash event in an inappropriate time.

 

 

Hardware

The phototransistor was mounted on the front of the robot near the top, and had side shields to avoid any false-triggers from nearby beacon sensors.

 

Circuit

 

 

The flash sensor circuit is made of an LTR-3208E NPN phototransistor in series with a 50K current-limiting resistor. The signal from the phototransistor is conditioned by passing it through a 74HC14 inverting Schmitt Trigger to create crisp edges. When a flash occurs, the output of the flash sensor circuit is logic level low and high at all other times.

 

 

 

 

 

 

 

 

Flash Detection in Software

An input capture was used to flag a flash event in software. This input capture was set to capture falling edges only, since the circuit design resulted in a low logic level whenever a flash occurred and it was assumed that the state would be high (a flash would not be happening) when the microcontroller was reset. After the flash event occurred and was handled in software, the input capture interrupt was disabled so that other flashes or close-proximity beacons would not appear as a flash event later in the game.

 

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