This paper selects STMicroelectronics' STM32F103RB, which is based on ARM's latest Cortex-M3 core, as the main control chip. By choosing an appropriate LCD module, a high-performance and low-power Chinese human-machine interface system is developed. The system is designed to be both efficient and user-friendly, making it suitable for various embedded applications.
1. Working Principle of the SystemThe system uses the STM32F103RBT6 as its core processor and employs the AM240320TFT LCD screen from Jingcai Optoelectronics for display purposes. Due to the limited internal flash memory (128KB) of the STM32F103RBT6, storing Chinese character fonts directly on the microcontroller would be inefficient and consume valuable resources. Therefore, the design utilizes the external SPI interface to store static Chinese character data in an external Flash chip. When needed, this data is transferred to the microcontroller via the SPI port. Since the STM32F103RBT6 lacks an FSMC interface, the software is used to simulate the bus for driving the liquid crystal module, ensuring compatibility and performance.
2. System Hardware Design 2.1 Power Supply CircuitThe entire system operates on a 3.3V power supply, so an external voltage regulator circuit is essential to stabilize the voltage. In this design, the LM1117-3.3 three-terminal regulator is used to convert the external battery voltage to a stable 3.3V. This power supply provides energy to the microcontroller, the LCD display, and the SPI Flash. A diode, IN4007, is connected in series with the positive power line to protect the system from reverse polarity. The schematic diagram of the power supply section is shown in Figure 1.
Figure 1 Schematic diagram of the system power supply
2.2 Circuit Design for Liquid Crystal DisplayThe liquid crystal display section is driven by the microcontroller, which controls the display module to show the human-machine interface. Initialization of the display module and the rendering of Chinese characters are handled through command words sent by the microcontroller.
2.2.1 Features of STM32F Series ARM MicrocontrollersThe STM32 processor is built around ARM’s latest V7 architecture, the Cortex-M3 core. Compared to the ARM7, it is one-third faster and consumes three-quarters less power. It includes features such as branch prediction, single-cycle multiplication, and hardware division, significantly enhancing its data processing capabilities. Additionally, it uses the Thumb-2 instruction set, which reduces code density and improves program efficiency. The STM32F103RBT6, selected for this project, runs at 72MHz and has built-in high-speed memory—up to 128KB of flash and 20KB of SRAM. It also features a rich set of I/O ports and peripherals connected to two APB buses, operating within a voltage range of 2.0V to 3.6V. These power-saving modes ensure that the system meets low-power application requirements while maintaining a balance between performance and energy consumption.
2.2.2 Characteristics of the TFT Liquid Crystal Display ModuleThe TFT (Thin Film Transistor) liquid crystal display is a type of active matrix display where each pixel has a semiconductor switch. This allows each pixel to be controlled directly by a dot pulse, making them independent and continuously adjustable. This design enhances the response speed of the display and enables precise control over the color levels, resulting in more accurate and vivid color reproduction. The TFT technology ensures a high-quality visual experience, making it ideal for use in human-machine interfaces where clarity and responsiveness are crucial.
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