The MCS51 series MCU At89S51 is used as the main controller. The peripheral circuit components include the digital tube driver, the output driver of the buzzer, the independent keyboard and the output of the LED. The digital tube driver uses two quadruple common cathode digital tube displays. Due to the limited driving capability of the single chip microcomputer, the 74HC244 is used as the driving force of the digital tube. A current limit of 100 ohms is connected in series on the 7-segment output line of the 74HC244. The buzzer is driven by a PNP transistor 8550, which is active low. The stand-alone button is connected using the pull-up circuit and outputs a high level when no key is pressed. The LED is connected in series with a 500 ohm resistor and then connected to the power supply. When the input is low, the LED is turned on. The hardware circuit schematic is shown in Figure 1. Lens Caps,Lens Cover,Camera Lens Cover,Camera Lens Cap SHAOXING COLORBEE PLASTIC CO.,LTD , https://www.colorbeephoto.com