Fig 1. Circuit of egg incubator's temperature control using AT89c51

This circuit works based on the fuzzy control algorithm that load in AT89c51. The output of controller is connected from port 2  AT89C51 to port 1 of AT89C2051 and p1.0 as sign bit. AT89c2051 is used to generate PWM signal, this signal is used to drive the heater and fan. The logic circuit is used to propagate PWM signal to heater if p1.0 low, and to fan if p1.0 high.

AT89c51 receives temperature information from LM335, after processed by ADC 0809.

The figure below is temperature control system response, when the loaded program is fuzzy-integrator.

Fig 2. Control system response using three different type of controller.