This article presents the design of a high-precision electronic scale that utilizes 24-bit A/D conversion technology. Accurate material measurement plays a crucial role in industrial production and trade, and weighing devices are essential tools for metrology. Modern electronic scales, which integrate sensor technology, electronics, and computer systems, offer fast, accurate, and user-friendly weighing solutions. They help reduce human error, align with legal metrology standards, and support process control in industries. As a result, they have gradually replaced traditional mechanical scales. The proposed design uses the AT89C52 microcontroller as the central processing unit, along with a resistance strain-type pressure sensor and the HX711 A/D conversion chip, to create a cost-effective, high-performance electronic scale suitable for various applications.
1. Structure and Working Principle of the Microcontroller-Based Electronic ScaleThe structure of the designed electronic scale is illustrated in Figure 1. The system works by converting the weight of the object into an analog voltage signal using a bridge varistor sensor. The voltage level varies proportionally with the weight. An NTC thermistor is also used to measure ambient temperature, ensuring accurate compensation for temperature variations. The HX711 A/D converter chip then converts this analog signal into a digital value, which is directly proportional to the weight. The AT89C52 microcontroller processes this digital data and displays the weight on an LCD screen. Users can input the unit price via buttons, and the microcontroller calculates the total price by multiplying the weight and unit price, displaying it on the screen as well. Additionally, the system supports printing features, allowing users to print out details such as weight, unit price, and total cost.
Figure 1: Structure of the Electronic Scale
2. Hardware Design 2.1 Bridge Varistor Sensor DesignFigure 2 shows the design of the bridge varistor sensor. This type of sensor works by detecting strain on a resistor, which changes the electrical resistance in response to applied pressure. These changes are then converted into a measurable voltage signal. After passing through a filter circuit, the signal is sent to the A/D converter for further processing. This ensures that only the relevant weight-related information is used for accurate readings.
Figure 2: Bridge Varistor Sensor
2.2 Filter Circuit DesignThe filter circuit shown in Figure 3 is designed to improve signal quality by reducing noise and ripple. It combines inductors and capacitors to form a more effective filtering system. Inductors are connected in series with the load to suppress large AC ripples, while capacitors are connected in parallel to bypass smaller ripples. This configuration enhances the stability of the output signal, making it smoother and more reliable. The filter helps minimize external interference, ensuring that the measured weight remains accurate even in less-than-ideal environments.
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