This paper presents a multifunctional precision electronic scale system that utilizes four foil strain gauges arranged in a Wheatstone bridge configuration to enhance measurement accuracy. The analog output from the HX711 integrated circuit, which is a high-precision weight sensor, is converted into digital signals through A/D conversion. These signals are then processed by a microcontroller unit (MCU) for accurate data handling. Various algorithms are implemented to perform different calculation functions, ensuring reliable and precise results. To improve user interaction, the system incorporates an LCD display, touch input, and voice broadcasting features, making the human-computer interface more intuitive and user-friendly.
2. System CompositionBased on the design requirements, the hardware of the system includes load cells, an AD conversion circuit, a microcontroller minimum system, key input module, display output, voice broadcast function, and a power supply module. The overall system block diagram is illustrated in Figure 1, providing a clear overview of the components and their interconnections.
Figure 1: Electronic Scale System Block Diagram
3. Load Cell Design 3.1. Cantilever Beam DesignThe cantilever beam used in this design is made from high-quality aluminum alloy with dimensions of 190mm in length, 20mm in width, and 3mm in height. Aluminum alloy is chosen for its excellent formability, moderate hardness, and good elasticity, making it suitable for use as a resistance strain gauge load cell. To optimize mechanical deformation and improve linear strain performance, the beam is designed with specific modifications:
(1) A small groove, approximately 1.5 mm deep, is machined near the fulcrum (about l/3 of the beam length) on the lower surface. This helps concentrate the deformation along a single line, resulting in better strain linearity.
(2) A 5 cm hole is drilled in the middle of the opposite end of the fulcrum, and a screw with a through-hole at the bottom is fixed in place. This ensures that the center of gravity of the measured object is concentrated at a single point, improving measurement accuracy and stability.
3.2. Measurement Circuit DesignThe measurement circuit employs a four-arm Wheatstone bridge configuration, which allows the system to compensate for external disturbances such as temperature and humidity. This setup significantly reduces the impact of environmental factors on the measurement results, thereby enhancing the overall accuracy of the system.
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 completes the load cell design, ensuring balanced and accurate signal output.
4. AD Converter DesignThe HX711 is a 24-bit A/D converter specifically designed for high-precision load cell applications. Compared to similar chips, it integrates essential peripheral circuits such as a regulated power supply and an internal clock oscillator, offering advantages like high integration, fast response time, and strong anti-interference capability.
The HX711 module is connected to both the Wheatstone bridge and the STM32 microcontroller. It converts the weak deformation signals from the Wheatstone bridge into digital signals, which are then sent to the STM32 for further processing and analysis. This ensures accurate and reliable weight measurements in real-time applications.
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