The object with fire is represented by light bulbs mounted with thermistor to detect the temperature drop when a fan is actuated. As the “candles” will be placed in the arena along with other objects, the robot will pause the SLAM process when a fire is identified by the phototransistor to extinguish the “fire”, then resume normal process.

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Fire detection and extinguishing involves using a phototransistor to detect light, and a fan to extinguish the fire. The phototransistor would be mounted on top of the fan, which is to be vertically connected to the servo motor and continuously scan for the light source.

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To detect the fire, a simple divider circuit with a phototransistor and resistor is used. The electrical property of phototransistors is that the resistance of the phototransistor decreases as the intensity of the light increases. Thus output voltage increases non-linearly with increasing light intensity. When the robot detects a light source nearby, the robot would stop and scan the area in front; at the highest voltage reading, the scan stops and the fan is set facing directly at the fire. The threshold of the voltage reading is set to 4.8V to ensure we can detect light source directly in front of the robot, while eliminating any peripheral light.

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To extinguish the fire, we use a 5V DC fan. The fan circuit consists of a fan connected in series with a NPN transistor, where 5V is connected to the collector, base to the Arduino PWM signal out pin and emitter connected to the fan. Voltage is injected into the base of the transistor to allow current to flow from collector to emitter (i.e. mains to fan), which would activate the fan at full speed. To control the speed of the fan we produce a PWM signal from the Arduino’s PWM pin into the base of the transistor. The PWM injects a high signal for a period of time allowing the current to flow through the transistor, and low for another period of time stopping current flow. To increase the speed we have a longer “high” period, while at low speed a longer “low” period is set.