This paper presents a multifunctional precision electronic scale system that integrates advanced sensor technology and microcontroller-based data processing. The system utilizes four strain gauges arranged in a Wheatstone bridge configuration to measure weight accurately. The analog output from the HX711 integrated circuit, which is specifically designed for high-precision load cells, is used for A/D conversion. This allows the system to collect accurate measurement data. The microcontroller, such as an STM32, processes this data and applies various algorithms to calculate weight and other related functions. To enhance user experience, the system includes an LCD display, touch input, and voice feedback, enabling a more interactive and user-friendly interface.
2. System CompositionBased on the design requirements, the hardware of the system consists of several key components: load cells, an AD conversion circuit, an MCU minimum system, a key input module, a display output unit, a voice broadcasting module, and a power supply module. These components work together to ensure accurate and reliable weight measurement. A block diagram of the system is shown in Figure 1, illustrating the overall architecture and signal flow.
Figure 1: Electronic scale system block diagram
3. Load Cell Design 3.1. Cantilever Beam DesignThe cantilever beam is constructed from high-quality aluminum alloy with dimensions of 190mm (length), 20mm (width), and 3mm (height). Aluminum alloy is chosen for its excellent formability, moderate hardness, and good elasticity, making it ideal for use in resistance strain gauge load cells. In this design, the beam undergoes specific modifications to optimize mechanical deformation and improve measurement accuracy.
(1) A small groove, approximately 1.5 mm deep, is machined into the lower surface of the beam near the fulcrum, located about one-third of the length from the fixed end. This helps concentrate the deformation along a single line, resulting in more linear strain distribution.
(2) At the opposite end of the fulcrum, a 5 cm diameter hole is drilled in the center, with a screw featuring a through-hole at the bottom. This design helps concentrate the center of gravity of the measured object at a single point, thereby improving measurement accuracy and stability.
3.2. Measurement Circuit DesignThe system employs a four-arm Wheatstone bridge configuration for the strain gauge measurement. This method provides effective compensation for external disturbances such as temperature and humidity, reducing the impact of environmental factors on measurement accuracy. By balancing the bridge, the system becomes more resistant to interference and delivers more reliable results.
The strain gauges R1 and R4 are mounted on the upper surface of the groove, while R2 and R3 are placed on the lower surface. This arrangement ensures balanced strain distribution and enhances the sensitivity and accuracy of the load cell.
4. AD Converter DesignThe HX711 is a 24-bit A/D converter chip tailored for high-precision load cells. Compared to other similar chips, the HX711 integrates essential peripheral circuits such as a regulated power supply and an internal clock oscillator. This high level of integration offers advantages like fast response time, strong anti-interference capability, and reduced complexity in the overall circuit design.
The HX711 module is connected between the Wheatstone bridge and the STM32 microcontroller. It converts the weak analog signals generated by the strain gauges into digital data, which is then processed by the microcontroller for weight calculation and other functions. This setup ensures high accuracy and real-time performance in the electronic scale system.
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