可燃性气体检测。以酒精为例，当传感器遇酒精气体时，电压生高，如此浓度继续升高，那么引起555输出震荡，当浓度降低时，555停止震荡 。-Combustible gas detection. Alcohol, for example, when the case of alcohol gas sensor, high voltage generation, so the concentration continues to rise, then the output of the shock caused by 555, when lower concentrations, 555 to stop the shock.