According to the application situation of current electronic scales, this paper analyzes a simple electronic scale device by using single chip microcomputer and AD574. Based on the analysis and measurement principle, a simple 51 series single chip microcomputer is selected as the main control system, and the sensor circuit is designed according to the measurement requirements. , AD conversion circuit, over-range alarm circuit, display circuit, button circuit, etc., according to the hardware circuit, completed the corresponding software design. 1, the principle of measurement The electronic scale generally consists of three parts, the load cell, the load-bearing system, and the force-return system. On this basis, it is divided into other hardware circuit sub-units, such as single-chip microcomputer minimum system circuit, sensor circuit, AD conversion circuit, over-range alarm circuit, display circuit, button circuit, storage circuit and so on. The measuring principle is: when the object is placed on the weighing platform of the load-bearing system, its weight parameter will be generated by the sensor to generate a pressure-electric effect, converted into an electrical signal corresponding to its weight, and then the electrical signal is amplified and passed through the amplifying circuit. AD processing, and finally the signal is input to the MCU processing, after the MCU processing, the input information is displayed on the LCD. The accuracy of the measurement is generally determined by the load cell. 2, hardware circuit design 2.1, overall design block diagram According to its measurement principle, the overall hardware block diagram of the design is shown in Figure 1. It mainly includes pressure sensor circuit module, amplification circuit module, AD conversion module, LCD display module, threshold alarm module, and single-chip control system module. Figure 1 hardware block diagram 2.2, sensor circuit design The design adopts SP20C-G501 ​​resistance strain sensor. The load cell is composed of combined S-beam structure and metal foil strain gauge, and has overload protection device. In the process design, the Wheatstone bridge is used for voltage acquisition and conversion. It can suppress the influence of temperature change, suppress the interference ability, and the compensation is convenient and simple. Therefore, the selected sensor has high precision, small zero drift and stable operation. The sensor schematic is shown in Figure 2: Figure 2 sensor working principle diagram How it works: When measuring with a strain gauge, attach it to the elastomer. When the elastic body is deformed by force, the sensitive grid of the strain gauge is also deformed, and the resistance value changes correspondingly, and is converted into a voltage or current change by the conversion circuit. Since the internal circuit uses Huygens bridge, when the elastic body is subjected to load deformation, the output signal voltage can be given by the following formula (1): 2.3, AD conversion circuit design The AD574 is a 12-bit single-chip A/D converter manufactured by Analog Devices, USA. It adopts a successive approximation A/D converter with a maximum conversion time of 25us and a conversion accuracy of 0.05%, so it is suitable for high-precision fast conversion sampling systems. The chip contains microprocessor interface logic (with three-state output buffer), so it can be directly connected to various types of 8-bit or 16-bit microprocessors without the need for additional logic interface circuits. It can be compatible with CMOS and TTL circuits. . The AD574 is available in a 28-pin dual in-line standard package. Figure 3 AD574 chip and wiring diagram with AT89s52 IoT 4G Gateway,IoT Smart 4G Gateway,Industrial IoT Gateway,Modbus Wireless Gateway,IoT WIFI Gateway Jiangsu Acrel Electrical Manufacturing Co., LTD. , https://www.acrel.com.pk
