Driven by the L298 chip constitute "24V DC Cooling Fan" of the drive circuit. Inside there are four inputs and outputs, mainly to enhance the amplitude of the input signal so as to enhance the role of the driving power. The circuit between the micro controller and the driver circuit isolation circuit constituted by PC817, has a protective effect on the micro controller. The "24V DC Cooling Fan" circuit should be noted that part of the two isolated circuits are not linked together, if you can not play together isolation. Scan the keyboard module keyboard scanner is scanning the keyboard to see if a key is pressed, if the key is pressed judge which one key when you want and press one button, "24V DC Cooling Fan" that the implementation of the infrared emission process. Scanning method is to determine the level of P1 mouth you, no button is pressed, you are high, when after a certain button is pressed, the bit that is low.