**What is an Electronic Scale?**
An electronic scale, also known as an electronic balance, is a weighing instrument that measures the mass of objects using principles such as Hooke's law or force. It can be categorized into three types based on its structural principle: mechanical scales, electronic scales, and electromechanical combined scales. The main components of an electronic scale include a load-bearing system (such as a weighing pan or scale body), a force transmission and conversion system (like a lever mechanism or sensor), and an indication system (including a dial or electronic display).
**Design of a Multifunctional Electronic Scale Based on STM32**
This project focuses on building a multifunctional electronic scale using the STM32 microcontroller. The system includes features such as price setting, weight calculation, total amount display, temperature measurement, voice output, and more.
**Subject Requirements:**
1. **Basic Part:**
- Set unit price via keyboard and display weight, unit price, and total amount simultaneously.
- Maximum capacity: 10.000 kg, with an error margin of ≤ ±0.1%.
- Use a TFT LCD to show weight, unit price, and total amount.
- Weight displayed in 5 digits (kg), max 99.999 kg.
- Unit price displayed in 5 digits (yuan), max 999.99 yuan.
- Total amount displayed in 6 digits (yuan), max 9999.99 yuan, with ≤ 0.01 yuan error.
- Include tare function and total accumulation.
- Store 10 types of commodity prices.
- Measure and display ambient temperature with ≤ 1°C error.
- Weigh between 0–10 kg.
- Provide voice output for results.
2. **Advanced Features:**
- Real-time clock with calendar (year, month, day, hour, minute, second).
- Power-down protection.
- High-precision A/D converter (HX711) for improved accuracy (≤ ±0.01%).
- Store product names and prices.
**Module Design:**
1. Main control chip module (STM32).
2. TFT LCD module.
3. Weighing module.
4. Voice broadcast module.
5. 24-bit AD HX711 conversion module.
6. Software part.
**Main Control Chip Module (STM32):**
The STM32F103 series is used due to its high-performance ARM Cortex-M3 core, up to 72MHz operating frequency, and rich peripheral interfaces. It supports multiple ADCs, timers, communication ports, and more.
**TFT Color LCD Module:**
A 320x240 resolution, 16-bit true color display with a touch screen. It uses a universal interface compatible with various development boards. The setup involves configuring the STM32 IO pins for communication with the LCD module.
**Touch Screen Functionality:**
Resistive touch screens use pressure sensing to detect touch points. They are durable, compatible with any object, and offer high accuracy through A/D conversion.
**Weighing Module:**
Uses a load cell connected to the HX711 ADC. For example, a 5V supply with 2.0mV/V sensitivity produces a full-scale output of 10mV. The wiring configuration is standard, and the installation method is typically a cantilever beam.
**Voice Broadcast Module (WT588D):**
This voice chip allows easy control of playback, volume, and looping. It supports PWM or DAC output. In this project, PWM is used for simplicity and sufficient sound quality. Voice files are generated using synthesis software and downloaded via SPI-Flash.
**24-bit AD HX711 Module:**
Designed for high-precision scales, it integrates power regulation, clock oscillator, and low-noise amplifier. It supports two input channels, programmable gain (64 or 128), and operates at 2.6–5.5V.
**Software Functions:**
- Initialize and control the TFT LCD.
- Display characters, numbers, and graphics.
- Manage the HX711 ADC for accurate weight readings.
- Handle voice playback via WT588D.
- Integrate all modules into a functional electronic scale.
**Conclusion:**
This project demonstrates a complete electronic scale system using STM32, combining hardware and software to achieve accurate weighing, user-friendly interface, and additional features like voice output and real-time clock. It’s ideal for applications requiring precision and multifunctionality.
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