This paper presents a high-performance, low-power human-machine interface (HMI) system based on STMicroelectronics' STM32F103RB microcontroller, which is built around ARM's advanced Cortex-M3 core. To enhance the user experience, an appropriate LCD module was selected to support Chinese character display and provide an intuitive interface.
1. System Working PrincipleThe system centers around the STM32F103RBT6 microcontroller, paired with the AM240320TFT LCD screen from Jingcai Optoelectronics for visual output. Given that the internal flash of the STM32F103RBT6 is only 128K, it would be inefficient to store Chinese font data directly on the chip. Therefore, this design leverages the external SPI interface to store static Chinese character data in an external Flash chip. When needed, the data is transferred via the SPI bus to the microcontroller. Since the STM32F103RBT6 lacks an FSMC interface, software-based simulation of the bus is used to drive the LCD module effectively.
2. System Hardware Design 2.1 Power Supply CircuitThe entire system operates on a 3.3V power supply, requiring a stable voltage source. In this design, the LM1117-3.3 three-terminal regulator is employed to convert the input battery voltage to a consistent 3.3V, ensuring reliable operation for the microcontroller, LCD, and SPI Flash. A diode IN4007 is connected in series on the positive power line to protect the system against reverse polarity. The schematic diagram of the power supply circuit is shown in Figure 1.
Figure 1: Schematic of the system power supply
2.2 LCD Circuit DesignThe LCD section is driven by the microcontroller, which sends commands to initialize and display characters on the screen. This process involves precise timing and command sequences to ensure correct display output.
2.2.1 Characteristics of STM32F Series ARM MicrocontrollersThe STM32F series microcontroller uses ARM’s latest V7 architecture, the Cortex-M3 core. It offers performance that is one-third faster than ARM7 while consuming only a quarter of the power. Features such as branch prediction, single-cycle multiplication, and hardware division significantly improve processing efficiency. Additionally, the Thumb-2 instruction set reduces code density and increases program execution efficiency. The STM32F103RBT6 used in this project runs at 72MHz, has 128KB of internal flash and 20KB of SRAM, along with multiple I/O ports and peripherals connected to two APB buses. It supports a wide voltage range of 2.0–3.6V and includes various power-saving modes, making it ideal for low-power applications without sacrificing performance.
2.2.2 Characteristics of TFT LCD ModuleThe TFT LCD module features thin-film transistors that act as switches for each pixel, enabling individual control through dot pulses. This allows for faster response times and more accurate color control, resulting in a clearer and more vivid display. The ability to independently manage each pixel makes TFT technology highly suitable for applications requiring high-quality visual output.
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