With the maturity of electronic weighing technology, electronic scales have gradually replaced old-fashioned weight measuring equipment. Because of its simple operation, accurate weight measurement, small size, fast measuring speed and convenient reading, it is widely used in commercial trade, hospitals, schools, enterprises and other departments. With the improvement of the manufacturing process, the electronic scale is becoming lighter and more portable, and people's pursuit of beauty is paying more and more attention to the changes of their body shape. Therefore, almost every family has an electronic weight scale. At the same time, with the arrival of the Internet of Things era and the development of WeChat technology, the Internet of Things technology will inevitably use more and more WeChat platform resources. This article introduces a weight management system based on WeChat platform. This system can not only measure weight, but also let users understand the changes in their weight. At the same time, using the WeChat platform, the system has a better experience of human-computer interaction, making the system more human and intelligent.
1. System overall structural designThe system takes 52 single-chip microcomputer as the core, the hardware part selects the differential full-bridge circuit by the resistance strain gauge, and the A/D conversion part selects the HX711 chip. In addition to the basic weight measurement function, the system proposes a function to save and analyze data based on WeChat platform, WiFi, and wit cloud platform. The system realizes saving and analyzing the weight information measured by the user, and returns the result to the user through the WeChat platform, and the user can also control the electronic weighing entity through WeChat.
Figure 1 System overall structure block diagram
2. Design of load cell 2.1, resistive strain gauge sensorThe most basic function of the weight management system is the measurement of body weight. Therefore, the load cell is one of the most important parts of the system, and its performance directly determines the important performance such as the accuracy and stability of the electronic weighing. Therefore, the system chooses to use a differential full-bridge circuit as the measurement circuit, which is composed of four resistance strain gauges. As shown in Figure 2, the four strain gauges are identical. When the bridge is open, the output voltage of the unbalanced bridge is:
Also, since R1=R2=R3=R4, and ΔR1=ΔR2=ΔR3=ΔR4 when force is applied, then: 101RU=ER∆, U0 is linear with ΔR1/R1, and the differential half-bridge circuit wireless error. The voltage sensitivity is SV=E and has temperature compensation.
Figure 2 Differential full bridge circuit
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