A microcontroller based on alarm device is developed for detecting a combine working station preventing crop conveying pipeline blocked by excessive feed-in quantity so as to avoid driving belt or driving wheel being damaged. An Atmel 89C2051 single chip microcontroller is employed as the core of the device to make the system simple in structure and small in size. Using Hall effect tachometric transducers detecting the magnetic induction pulses induced by magnetic steel pieces attached on belt wheel, the wheel rotate speed is detected. Moreover, with some filtering measures and logical judgements, pseudo pulses are filtered out. According to the measured speed, the belt wheel spin tendency is estimated, at the same time, audible and visual alarm signal are also emitted to warn operator to reduce the operating speed so that wheel blocking and belt spin are avoided, thus crop loss is reduced. The system achieves a low cost, high reliable equipment for detecting combine working station automatically with acousto-optic alarm.