introduction
Among various devices, display devices occupy an important position. Less display devices are like people with fewer eyes, and many internal things are invisible. Display devices are important and common, yet their shape is always monotonous, like a model. The rotating LED screen attracts the eyes of electronic enthusiasts with its novel 360° viewing angle. This project is through the main control chip STM32F103, the touch technology and the rotating LED screen can be combined to realize the clock conversion. You can also use the touch technology to play some small games on the rotating LED [1], so that the rotating LED is no longer just a single Ornamental technology.
Rotating LED display is a new type of display that realizes graphic display by synchronously controlling the position and lighting state of light-emitting diodes (LEDs). It has been rapidly developed due to its novel structure, low cost and 360° viewing angle. . At present, the common LED display screens are displayed by scanning mode. The realization principle is to control different batches of LEDs to illuminate in different time periods. According to the visual persistence characteristics of the human eye, when the scanning frame rate reaches 24 Hz. Above, the human eye does not feel the scanning process, but a stable image. The rotating display screen realizes the graphic display by controlling one row or one column of LEDs to quickly move the position and change the lighting state. If the LED is rotated fast enough at each position, a stable image can also be displayed. The principle of POV (ie, the principle of visual detention) is used for display screens. The advantage is that the display can be realized with a small number of LEDs in a traditional way. The MCU is used to control the LED, and the touch button provides the user to interact with the system. The landscape in which the rotating LED floats in midair gives the visual enjoyment.
Based on this status quo and principle, this paper proposes a rotating LED screen display controller design based on TI's TLC5947 driver chip and STM32F103. The rotating LED screen adopts the principle of human eye visual frequency retention, and the rotating LED virtual screen is manufactured under the precise control of the microcontroller, and a small amount of LED can completely realize a new display technology that can be realized by the mass LED in the traditional mode. The rotating three-primary full-color LED is based on the RGB principle. By changing the hue, saturation, and intensity of the three colors, the highest-color image display of up to 36 colors can be realized, thereby making the display more splendid. Compared with flat panel LED display and other display technologies (such as CRT, LCD, PDP), the rotary LED array has several obvious advantages such as low cost, high resolution and low power consumption [2]. .
1 system hardware design
The STM32F103 is connected to the LED [3] via TLC5947 to control the display of the LED light on the rotating board. For example, the STM32F103 can be used to control the LED light to display the clock pattern or various graphics [4]. If conditions permit, some simple games can be displayed. The LED is connected to the ARM processor, and the display mode of the LED lamp is changed by the processing of the touch signal by the ARM processor, and the change from the ground state pointer clock to the digital display type and the background of the display thereof can also be performed. Calibration operation. The TLC5947 drives the rotating LED screen display control circuit as shown in Figure 1 [5].
Figure 1 TLC5947 drives rotating LED display control circuit
1.1 Introduction to STM32F103
The STM32F103 controller is selected. The STM32F103 is an enhanced series with a maximum operating clock frequency of 72 MHz. It has an ARM CortexM3 core, 128~256 KB Flash, 20~48 KB RAM, 8 MHz CPU crystal, 32.768 kHz RTC crystal and rich Peripherals (64 fast I/O ports) and 4 GB of linear address space. The emulator used by ARM is very expensive, and the debugging tools of the MCU are very cheap. In contrast, the CortexM3 reference microcontroller has a dedicated pin for debugging, which saves a lot of manpower and resources. The CortexM3 integrates most of the memory controllers so that Flash can be connected directly outside the MCU, reducing design challenges and application barriers. The CortexM3 processor combines a variety of breakthrough technologies to enable a combination of low power, low cost, and high performance. Programming supports ISP download function, can be powered by USB port and JLINK emulator, it is very convenient to use [6].
1.2 Introduction to TLC5947
The TLC5947 is a 24-channel, 12-bit PWM pulse-width modulated LED driver chip from TI (Texas Instruments). The TLC5947 is available in an advanced package with an ultra-small 32-pin QFN [7]. It provides accurate constant current values ​​for LEDs, with a channel-to-chip difference of only ±2%; high-speed transfer rates (30 MHz for a single chip, cascading at 15 MHz); interleaved time lag between output channels To avoid transmission error; the chip has a temperature detection system inside, when the temperature of the chip is too high, in order to protect the chip, it will automatically disconnect all output channels, when the temperature returns to normal, the chip works normally; the chip supports cascading, Multiple chips can work together to drive larger LED display screens. The current value of the 24 channels is set by the resistance between the external IREF and ground. The resistance in the driver circuit is determined by the current of the LED lamp being driven. The chip has a wide operating voltage of 3?0~5?5V and contains an internal crystal of 4 MHz. The TLC5947 is suitable for driving full color LEDs and displays.
1.3 LED display
Three-color (RGB) LED lights are used to achieve multiple color light sources and colorful output. At the same time, the LED itself also has the functions of considerable stability, high efficiency, high single color purity, and adjustable light intensity. The LED is connected to the ARM processor, and the display mode of the LED lamp is changed by the processing of the touch signal by the ARM processor, and the time is changed from the ground state pointer clock to the digital display type, and the background of the display is changed, and the time can be performed. Calibration operation.
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