Design of home-school communication system based on Hetai single chip microcomputer

    At present, the common ways for parents of primary and secondary school students to contact teachers include parent meetings, phone calls, teacher home visits, parents coming to school, parents signing, etc. These traditional methods have drawbacks and their effects are not ideal. Now many schools use the Aibetong system, but the shortcomings of this system are also obvious. Its functions are relatively simple and it only provides information when students arrive and leave school.

    The function of using text messages to notify parents. In addition, it uses the working mode of IC card. Before swiping the card, there are often many students scrambling for each other, which wastes time and is prone to safety accidents. Students are likely to forget to swipe the card and make parents anxious. Even some senior students who do not like parental constraints will lie to their parents and say that the school's card swiping machine is broken. Therefore, the market promotion of this system in schools is not ideal.

    In view of the above problems, a home-school contact system based on HOLTEK single-chip microcomputer is designed. It can be used by teachers and parents to establish daily contact very conveniently, and can effectively supervise students' learning at school and at home, greatly saving the time for teachers and parents to contact each other. Parents can also use passwords to sign electronically. The system adopts radio transceiver mode, which can automatically record the time of arrival and departure from school, overcomes the shortcomings of the Aibetong system, and can completely replace the Aibetong system. It has a bright market prospect and will be welcomed by teachers and parents. It will definitely obtain high returns after promotion and operation.

    1 Hardware Design

    The hardware of the system mainly consists of two parts: the student extension system and the teacher background system. As shown in Figure 1, the hardware of the student extension system mainly consists of the HT46RU24 microcontroller, display/keyboard, serial port circuit , data storage , battery voltage detection module and wireless module. As shown in Figure 2, the teacher background system mainly consists of the HT46RU24 microcontroller, PC, serial port circuit and wireless module.

    1.1 HT46RU24 MCU

    The core component of the home-school communication system is the HT46RU24 microcontroller, which is a low-power, high-performance 8-bit microcontroller developed by HOLTEK. Its ROM is 8K×16 B, RAM is 384 B, and there are 28 bidirectional I/O ports. In addition, it also has 8-channel 12-bit resolution A/D conversion. A/D conversion can be used to monitor external analog signals, such as detecting battery voltage, current, temperature, humidity, pressure, brightness, etc. 2 modes of PWM output are provided, which can be applied to temperature control, speed regulation, constant voltage, constant current, etc. Controllable PFD output is used for sound, or infrared

    The carrier signal for transmission. The UART of the HT46RU24 is a full-duplex asynchronous communication, the baud rate can be set by software, and it has an automatic error detection function. When using the UART to transmit data with other systems, the burden on the software can be reduced and the efficiency of the entire system can be improved. In addition, the HT46RU24 microcontroller has a built-in ADC to detect the battery voltage, which can display the battery power consumption and remind you to replace the battery in time to avoid failure of the extension due to insufficient battery power.

    1.2 Keyboard/Display

    The keyboard hardware circuit of the system is mainly composed of 4×3 keys, including numeric keys 0~9, reset key, PC and MCU communication key, known model confirmation key, and automatic test key. In order to save I/O ports, the LCD data bus is shared with the 4×4 keyboard. The display hardware circuit is composed of LCD. The LCD is DM12232F, which is a graphic dot matrix liquid crystal display. It is mainly composed of row driver/column driver and 122×32 full dot matrix liquid crystal display. It can complete 16×2 (16×8 dot matrix) ASCII code display and 7.5×2 (16×16 dot matrix) Chinese characters. The interface with the external CPU can be controlled in parallel and powered by 5 V. The Chinese character display occupies one byte, while numbers, English letters and four arithmetic symbols can be displayed using half a byte width. When arranging the screen display, the addresses 80~82h and 90~92h are used as fixed Chinese characters for displaying models and results, the remaining addresses in the first row are used as the number of models to be displayed, and the remaining addresses in the second row are used as the results to be displayed. The main function of the keyboard/display module is to realize the electronic signature of parents. The keyboard module is used to input the password, and the display module is used to display the homework content, correct password and incorrect password information. The hardware circuit of the keyboard/display is shown in Figure 3.

    1.3 Serial port circuit

    The serial port circuit is designed with MAX232 chip. The design scheme is to connect MAX232 with the universal asynchronous receiver/transmitter pin of the microcontroller. Because the RS 232 level of the computer serial port is -10~10 V, and the signal voltage of HT46RU24 is TTL level 0~5 V, MAX232 is used for level conversion. The device contains two drivers, two receivers and a voltage generator circuit to provide TIA/EIA-232-F level. The circuit diagram of the serial port circuit is shown in Figure 4.

    The serial port circuit is mainly used to complete the communication between the HT46RU24 microcontroller and the PC. Teachers can use VB, VC, etc. to design the serial port communication interface on the PC, and input the edited homework into the HT46RU24 microcontroller of the background system through the serial port circuit. Similarly, parents can also edit the message on the PC and input the message into the HT46RU24 microcontroller of the student extension through the serial port.

    1.4 E2PROM

    The chip used here is AT24C256. AT24C256 is an E2PROM with I2C bus structure. It has the characteristics of compact structure and large storage capacity. In addition, the use of I2C interface chip can save I/O ports. The AT24C256 memory chip has a storage capacity of 256 KB, paging storage, each page has a capacity of 64 B, and the address range is 0000h~7FFFh. The main function of E2PROM is to complete the storage and reading and writing of information such as homework and parent messages. The hardware circuit is shown in Figure 5.

    1.5 Wireless Module

    The wireless module uses the nRF2401 chip, which has an operating voltage of 3.3 V. It is a single-chip RF transceiver chip that operates in the 2.4-2.5 GHz ISM band. It has built-in frequency synthesizers, power amplifiers, crystal oscillators, modulators and other functional modules. The output power and communication channels can be configured through the program. The wireless module provides one-way wireless transmission and two-way wireless reception functions. It is directly plugged into the microcontroller target board through a 10-PIN interface and can be used very conveniently. Use the wireless module for multi-machine communication to realize the automatic roll call function and layout

    The circuit of the wireless module is shown in Figure 6.

      2 Software Design

    The whole system is composed of two HT46RU24 microcontrollers and a PC. According to the hardware structure, the software process is divided into three parts: extension software process, background software process and PC software process.

    The extension software flow is shown in Figure 7, which is the basic flow to realize the functions of wireless transceiver, key display processing, serial communication, etc. of the student extension system. The background software flow is shown in Figure 8, which is the basic flow to realize the functions of wireless transceiver of the background system and serial communication with the PC. The PC flow is shown in Figure 9, which is the basic flow to realize the functions of wireless transceiver control, serial communication, and information display of the PC.

    3 Debugging Results

    After the software and hardware are successfully debugged, the system can fully realize the expected functions. As shown in Figure 10, parents can leave messages through this interface; as shown in Figure 11, teachers can assign homework, electronically call the roll, and view parent messages through the teacher background interface; as shown in Figure 12, the display module can realize the function of viewing the homework assigned by the teacher on the student extension; as shown in Figure 13, the parent electronic signature function can be realized on the display/keyboard module, and parents can also reset the password using the keyboard.

    4 Conclusion

    In short, the system makes full use of modern technical means to solve the problem of communication between primary and secondary schools, and can complete functions such as editing information, sending data in both directions, displaying data, and saving data. This method has fast information transmission, is easy to carry, easy to operate, low cost, and complete functions. It greatly facilitates the communication between teachers and parents, and does not occupy teachers' spare time, which is of great practical significance.