4. System operation
Fig. 1 presents the major functional units of the system. The hardware and software of the system must cooperate with each other to display efficiently the specified image on the wheel. The speed and angle of rotated are calculated using an STM32 ARM microcontroller to ensure that the image is stably displayed. The efficient control of hardware and software depend on accurate knowledge of the operational flow of the system.
4.1. System operation slow
Fig. 2 presents the operational slow of the image display system. The LED lighting strip executes the image display processes. The proposed system initializes all of the hardware devices and software programs when the system is booted. The two control modes of this system are the manual control mode and the remote control mode. The manual control can be set using the external button on the main control board. Another remote control is executed by a mobile APP that is installed on a mobile phone, over a Wi-Fi connection. The application program can establish a connection between the mobile phone and the main control board. When the main board receives packets from the mobile APP it determines which image will be generated by the LED lighting strip.
These two control modes select the corresponding image patterns that are stored in the memory of the STM32 microcontroller. An interrupt delay ensures that the imaged patterns are transmitted at the correct time from the main control board to the LED lighting module. The interrupt delay changes with the rate of rotation of the wheel. The interrupt delay is shortened as the rate of rotation increases to ensure that the displayed image is as specified. Therefore, the rate of rotation in all instances dominates the interrupt delay to display an image.
4.2. Hardware interface
Several hardware components for this system are developed. They include the main control board and three LED lighting strips. Three LED lighting strips perform the LED imaging function on the wheel; pairs of boards are separated by an angle of 120 degrees. The two kinds of major circuit board that perform the imaging function are described as follows.
(a) Main control board Fig. 3 presents the main control board. The board receives control commands from the remote application program and executes the imaging algorithm. before transmitting the control signals to the LED lighting strips. The main control board also receives feedback signals from the speed sensing device. The ARM STM32 microcontroller provides the major communication interface between circuit boards and executes the imaging algorithm to control the LED image that is displayed on the wheel. General-purpose input/output (GPIO) ports in this board connect the board to other circuit boards. A wireless network module (Wi-Fi) is also deployed in the main control board to transmit commands or data between the main control board and the mobile APP
(b) LED lighting strip
Fig. 4 presents the designed LED lighting strip. The LED lighting strip comprises sixteen LED chips. The system comprises three LED lighting strips that display the image. The size of the wheel determines the numbers of LED chips and the length of the light column. A larger wheel needs more LED chips to display the image. Each LED lighting strip has three decoding ICs (or called decoders) to resolve the incoming packets and the control commands from the STM32 microcontroller on the main control board. The decoders receive the control commands, decode them, control the corresponding LED chips, and set their colors. The strip uses an I/O expander to control all LED chips.
43. Software interface
Fig. 5 presents the graphic user interface of the Android-based mobile application program. The mobile APP is installed on a mobile phone. When the Wi-Fi wireless network connection function on the phone connects the corresponding Wi-Fi interface on the main control board, the cyclist can control the LED lighting strip on the spokes of the bike. The mobile APP firstly enters the basic mode in which the user can select one of six patterns. When the user selects a pattern, the LED lighting module displays that pattern once the rotational speed of the wheel reaches a particular value. The advanced mode also enables the user to set a cycle of warious patterns and the duration of each.
The LED lighting strip is controlled by the mobile APP via a Wi-Fi wireless network. The control program of the LED lighting strip is installed in the main control board. Commands from the control interface and feedback information from the LED module are packaged using the TCP/IP and Wi-Fi protocols for wireless communication. A specific packet format is used for communication between the mobile APP and the main control board. The sockets of the Android operating system Mobile Control Program; Mobile application program