There are many coal gas alarm’s devices in our lives. These devices will alarm after the coal gas leaking. We call them household or industy appliances. This paper introduces the design of a coal gas alarm’s device that use the AT89S52 SCM as the most important controller. It is a core-components that control the whole programs and circuit of the coal gas alarm’ device. The appliance monitors the density of coal gas with the sensor of NAP-505 and compares the current density with the setting density. We get the control signal through the dealing with the deviation signal and then sent a alarm signal that is memoried in a RAM of DS12887. The analog signal of eight densities of the coal gas are transformed into the digital signal with the A/D converter, in addition which is cotrolled with the keyboard. We can monitor the leak of coal gas in the house or industy. The hardware design of circuits is reasonable and the performance of the coal gas alarm’s device is safe and reliable.
