This article presents the design of a high-precision electronic scale that utilizes 24-bit A/D conversion technology. Accurate material measurement is essential in industrial production and commercial transactions, and weighing devices play a crucial role in metrology. Modern electronic scales, which integrate sensor technology, electronics, and computer systems, offer advantages such as fast weighing, clear digital display, and ease of use. They help minimize human error and align with legal metrology standards and process control requirements. As a result, they are gradually replacing traditional mechanical lever scales and becoming the mainstream solution. The design described here employs the AT89C52 microcontroller as the central control unit, along with a resistance strain-type pressure sensor and the HX711 A/D conversion chip, to create a cost-effective and high-performance electronic scale.
1. Structure and Working Principle of the Microcontroller-Based Electronic ScaleThe structure of the electronic scale is illustrated in Figure 1. The working principle involves the bridge varistor sensor, which converts the weight of the object into an analog voltage signal. The strength of this signal corresponds directly to the weight of the object. An NTC thermistor is also used to measure ambient temperature, ensuring accurate compensation for temperature variations. The HX711 A/D converter chip processes the analog signal and converts it into a digital value, which is proportional to the object’s weight. The AT89C52 microcontroller receives and processes this digital data, displaying the measured weight on an LCD screen. Users can input the unit price using buttons, and the microcontroller multiplies the weight by the unit price to calculate and display the total cost. Additionally, the system supports printing features, allowing users to print details such as weight, unit price, and total amount.
Figure 1: Structure of the electronic scale
2. Hardware Design 2.1 Bridge Varistor Sensor DesignFigure 2 shows the bridge varistor sensor, which is a key component in the system. This sensor uses strain gauges to detect deformation caused by applied pressure, converting it into electrical parameters. These signals are then filtered through a dedicated circuit before being sent to the A/D converter for further processing.
Figure 2: Bridge varistor sensor
2.2 Filter CircuitThe filter circuit used in this design is shown in Figure 3. It consists of inductors and capacitors arranged to reduce ripple and noise in the signal. The inductor, which has high AC impedance, is connected in series with the load to suppress large voltage ripples, while the capacitor, with low AC impedance, is placed in parallel to bypass the remaining ripple current. This combination of inductive and capacitive filtering improves signal stability, reduces pulsation, and enhances the system's resistance to external interference, resulting in more accurate and reliable measurements.
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