For design "Small Cooling Fan" SCM central processing system, according to the requirements, we can choose to have within 4KB chip E2PROM of AT89C51 microcontroller as the central processor. Temperature sensor can choose LM324A operational amplifier, the "Small Cooling Fan" designed proportional control regulator, the output voltage is proportional to the resistance of the thermistor, but this solution requires multiple samples can accurately detect the rear, too cumbersome . So I used the more excellent DS18B20 digital temperature sensor, "Small Cooling Fan" can directly simulate the temperature signal into a digital signal, reducing the complexity of the circuit, improving the operational quality of the circuit.