The necessity of introducing EDA software into SCM course design
With the rapid development of modern electronic technology, SCM has been widely used in industrial control and consumer electronic products. As an application-oriented course, in the teaching process of SCM course, it is necessary to teach students certain theoretical knowledge in limited classroom time, and give students practical space to give full play to their hands-on ability in practice teaching. Especially in the course design process, due to the short design cycle (generally two weeks) and students’ lack of practical design experience, the previous method is that the teacher gives the circuit schematic diagram, and then the students “follow the picture” in the test box or bread board, and finally see the experimental phenomenon is considered successful. In this way, many students do not understand the experimental principle, let alone design or innovate, and the actual teaching effect is not ideal. The main reason is that the efficiency of students in the design process of hand drawing circuit diagram is low, and when the bread board is full of wires, it will be very troublesome to check the error or modify the circuit parameters, which greatly hit the students’ creative enthusiasm, so the actual effect is not very good. However, the introduction of EDA software, through the powerful computer aided design ability, can greatly improve the efficiency and accuracy of circuit design, students can adjust and modify the parameters of the designed circuit at any time, greatly enhance the students’ interest in learning and creative enthusiasm, so as to improve the teaching effect of practice teaching.
2 example of course design — 4-digit digital display instrument
In order to explain the application of Protel software in SCM course design in detail, this paper takes 4-digit digital display instrument as a specific example to explain the design method and design process of SCM circuit in detail. This example comes from the actual engineering project. After being introduced into the course design, it has been appropriately simplified, but it requires students to complete most of the design work independently. The circuit form and parameters designed by each student can be different. The key is to master the design idea and method of single chip microcomputer circuit. The specific design process is divided into functional module division, circuit schematic design, PCB design, circuit board manufacturing, circuit board welding debugging and other steps. The teaching goal is to let students master the design idea and general method of single chip microcomputer circuit through this course design, which can be used as a reference for practical circuit design in the future.
2.1 introduction of functional modules
The main function of the 4-bit digital display instrument is to send the analog signal collected by the sensor to the AD converter for AD conversion after conditioning and amplification; the single chip microcomputer calculates and processes the AD conversion result, drives the 4-bit digital tube to display the collected data, and has the function of overrun sound and light alarm (driving buzzer and relay) and communication with PC (RS232). In order to achieve the above functions, the 4-bit digital display instrument is divided into 6 functional modules: signal conditioning module, AD conversion module, MCU main control module, display drive module, communication module and power supply module. In the actual course design process, according to the specific situation of students, they can be asked to choose some of the modules, or adopt the form of group division of labor and cooperation. In the teaching method, we should pay attention to the requirement that students must adopt the method of block design and block debugging, first the part and then the whole, instead of starting debugging after the whole system is completely built, otherwise, it will be more difficult to check if there are errors.
2.2 function module design
(1) Signal conditioning module and AD conversion module.
The signal conditioning module uses two OP07 to condition and amplify the analog signal input by the sensor, and then send it to the AD conversion module for AD conversion. The AD converter uses 24 bit AD converter cs5550 to convert the analog signal into digital signal, and then send it to the MCU for calculation and processing.
(2) MCU main control module.
The main control module uses stc11f16xe enhanced 51 as the control core of the system. Its pins and functions are compatible with the traditional 51 single chip microcomputer, but the instruction execution speed can reach 12 times of the traditional 51. In addition, some other functions are added. The minimum system schematic diagram of stc11f16xe is similar to that of traditional 51. Most MCU textbooks have detailed introduction, which can be drawn by students themselves after consulting.
(3) Display driver module.
The display driver module uses CH452 and ULN2803 to drive 4-bit common positive 8-segment nixie tube. The reason why CH452 is used is that it occupies less MCU port line and the driving method is relatively simple. Students can also use 74HC595 or IO port with triode to drive in the design process. Here, we need to remind students to pay attention to the total driving current that the driver chip can bear, so as to avoid burning the chip.
(4) Communication module.
The communication module uses MAX232 chip to realize the communication with PC. In the course of curriculum design, the corresponding host computer communication software is provided to students by teachers to detect whether the communication module works normally. The design of this module can deepen students’ understanding of RS232 communication principle, and master the most basic communication handshake protocol format.
2.3pcb board design and circuit board making
In the past course design of single chip microcomputer, when the circuit schematic diagram is drawn, students use breadboard or universal board and wire to make circuit board, which has low efficiency and is very troublesome to find out when there are errors. After the introduction of Protel software, the components in the circuit diagram can be imported into the PCB diagram and drawn, and then the circuit board can be made by heat transfer printing and PCB engraving machine. The circuit board made in this way is more exquisite, and the manufacturing efficiency is also higher. Because there is no additional wires, it is more convenient to find errors and modify circuit parameters.
2.4 welding and debugging of circuit board
Under the guidance of teachers, students gradually complete the welding and debugging of the circuit board. In this process, attention should be paid to the training of students’ practical ability, from the selection of components, judgment of good or bad, block welding and debugging according to the circuit function, to the final realization of the overall function of the electronic tug of war device.
In the practical teaching of SCM course design, the introduction of EDA software for aided design can not only greatly improve the design efficiency and success rate, but also stimulate students’ interest in learning and innovation ability, and the teaching effect has been significantly improved. And these design ideas, design processes and design methods can be applied to the practical circuit design in the future work, which has a strong practical application value.
Editor in charge: Tzh