A fuzzy logic system that controls the temperature of a room has been successfully designed and built. The temperature of the system is measured by a thermistor and a bridge circuit. The fuzzy logic algorithm utilizes fuzzy rules, membership functions, and a look-up table to generate a particular gain used to determine the duty cycle of the pulse width modulated signal that is sent to the switching circuit. A solid state switch is used to switch the heating element on and off as dictated by the duty cycle of the TTL level square wave. The fuzzy logic algorithm was written in 6809 assembly code on the modular computer. 
 

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