Multifunctional circuit module design

0 Introduction

Electrical courses represented by "Circuit Fundamentals" are core basic courses for mechanical, electronic, and automotive majors in higher vocational colleges. Due to the abstract principles, complex content, and strong applicability of such courses, students in higher vocational colleges now have a lower starting point than undergraduate students and have a slightly poorer ability to accept and understand. Although the courses have corresponding experimental training, the integrity of the experimental training equipment teaching module and the convenience of the operation process cannot allow students to truly contact and understand circuits. The current problems of students being difficult to learn and teachers being difficult to teach in electrical courses in higher vocational colleges are becoming increasingly prominent. The multifunctional teaching circuit module integrates the construction, analysis, and design of actual circuits into the teaching of basic core professional courses, which can essentially solve the problems existing in students' learning.

The multifunctional circuit module is a multi-mesh circuit constructed by printed circuit boards, electronic components, signal sources, electrical instruments, etc. In the circuit design, each branch has a reserved jack. The signal source type can be adjusted according to the needs of the classroom teaching process to construct different circuit types such as single-power supply or multi-power supply DC circuits and AC circuits. Each branch is connected in series with an ammeter and in parallel with a voltmeter to detect the circuit parameters of each branch and each component. The multifunctional circuit module has the external connection of the signal source and the adjustability of the circuit structure. It can be flexibly used in the teaching process of the "Basics of Circuits" courses in mechanical, electronic and automotive majors in higher vocational colleges, so that different projects can be constructed for teaching at different teaching stages. Focusing on specific projects, a "theoretical and practical integration" teaching model that integrates "teaching, learning and doing" can be carried out.

At the same time, the construction and design of multifunctional teaching circuits allow students to get to know various electronic components in real life, and to construct and analyze the structure and performance of various circuits from easy to difficult. This can stimulate students' curiosity and interest in learning while improving their hands-on skills, and ultimately train and cultivate students' basic ability to detect, analyze and design circuits.

1 Multifunctional teaching circuit design scheme

"Electrical and Electronic Technology" and "Circuit Fundamentals" are professional basic courses for the first semester of electronics, communications, mechanics, and automobiles in higher vocational colleges. The multi-functional teaching circuit module is used to train students in real scenes to have a specific understanding of the performance of basic electronic components in circuit courses, the welding construction of multi-mesh circuits, the operation and use of electronic instruments, multi-environment monitoring of the main physical quantities of circuits, physical verification of basic circuit laws, and quantitative analysis of various circuit analysis methods such as superposition theorem, Thevenin theorem and Norton theorem.

As shown in FIG1 , a multifunctional teaching circuit device includes a basic circuit, a signal source, instruments, etc.; the signal source includes a DC voltage source, a DC current source, a sinusoidal AC power supply or other non-sinusoidal power supplies; the basic circuit includes five sockets and three resistors R1, R2, and R3; the instruments can be an ammeter, a voltmeter, an oscilloscope, etc.

2 Analysis of the Multifunctional Teaching Circuit Module

FIG2 shows a multifunctional teaching circuit module, which is composed of three resistors and five power strips. As can be seen from the figure, due to the reasonable distribution of the power strips, the three resistors are independent of each other. After the power strips are connected to the wires, they can be short-circuited or disconnected, and can also be effectively connected to other instruments or signal sources.

2.1 Measurement Analysis of Kirchhoff’s Law

Figure 3 shows that the basic circuit is connected to the power supply and instrument. Specifically, the 12 and 78 sockets are connected to the voltage sources u1 and u2 (either DC power or AC power), respectively. They can also be connected to a current source. The 34, 56, and 910 sockets are connected to the ammeter, which are the branch currents of the three branches respectively. It should be noted here that if the power supply is a DC source, the direction of its connection should be considered. Generally speaking, the current flows into the positive terminal of the ammeter and flows out of the negative terminal. Therefore, the branch current of the circuit can be calculated before connecting the ammeter. In this way, the test results and calculation results can be used for error calculation to verify Kirchhoff's current theorem, that is, at any time, the sum of the branch currents flowing into any node in the circuit is zero.

Connect a voltmeter between 23, 67, and 59. If the power supply is a DC source, the direction of the voltage should also be considered when connecting it. However, since we have calculated the current size above, the connection direction of the voltmeter and the ammeter is the same. In this way, the voltage of each component in the entire circuit can be measured to verify Kirchhoff's voltage theorem, that is, for any loop, at any time, the algebraic sum of all branch voltages along the loop is equal to zero.

If 12 and 34 are connected to an AC power supply, the results of the voltmeter and ammeter are their effective values. We can analyze from the measurement results that Kirchhoff's law can also be applied to AC circuits.

2.2 Measurement Analysis of the Superposition Theorem

The content of the superposition theorem is: in a linear circuit, the voltage or current of any branch can be regarded as the algebraic sum of the voltage or current generated in the branch when each independent power source in the circuit acts alone. In Figure 3, voltage sources u1 and u2 act together. On the basis of Figure 3, 12 can be short-circuited, u2 acts alone between 78, and the others remain unchanged. The branch current under the action of u2 alone and the voltage of the resistor can be measured; similarly, 78 can be short-circuited, u1 acts alone between 12, and the others remain unchanged. The branch current and the voltage of the resistor under the action of u1 alone can be measured; the measured results should be equal to the results in Figure 3 after superposition, which verifies the superposition theorem.

In FIG3 , a voltage source and a current source may work together. It should be noted that if the voltage source works alone, the current source should be short-circuited.

2.3 Measurement Analysis of Thevenin’s Theorem and Norton’s Theorem

Based on Figure 3, the 9th and 10th sockets are disconnected, that is, the resistor R3 is disconnected. How to use the Thevenin theorem or Norton theorem to quantitatively analyze the current and voltage of the resistor R3?

Thevenin's theorem states that any active two-terminal network can always be replaced by an actual voltage source consisting of a voltage source Us and a resistor Rs in series, where: the voltage source Us is equal to the open-circuit voltage Uoc of the active two-terminal network, and the internal resistance Rs is equal to the equivalent resistance R0 after all independent power sources in the network are set to zero (voltage source short-circuited, current source open circuit).

Norton's theorem states that any active two-terminal network can always be replaced by an actual current source consisting of a current source Is and a resistor Rs in parallel, where the current source Is is equal to the short-circuit current Isc of the active two-terminal network, and the internal resistance Rs is equal to the equivalent resistance R0 after all independent power sources in the network are set to zero (voltage source short-circuited, current source open-circuited).

As shown in Figure 3, after 9 and 10 are disconnected, a voltmeter is connected between 58 to measure the open circuit voltage Uoc; if a current source is connected between 58, the short circuit current Isc can be measured. Remove the power supply of the 12 and 78 sockets (removing the voltage source is equivalent to a short circuit; if it is a current source, it is an open circuit.), connect a multimeter between 58 and set it to the resistance range, and the equivalent resistance R0 can be measured. In this way, the current and voltage of the resistor R3 can be solved according to the equivalent circuit, and the results can be compared with the voltage and current measured by R3 in Figure 3.

In addition, if the 12th and 78th sockets are connected to AC power, the 34th, 56th, and 910th sockets can be connected to an oscilloscope individually to observe the size and graph of each branch current; 23th, 67th, and 59th sockets can also be connected to an oscilloscope to observe the size and graph of the voltage of each resistor.

3 Conclusion

Due to the integrity of this teaching circuit and the convenience of the operation process, students can complete the welding of the basic circuit by themselves, and can also verify the principle on the circuit they have welded, and truly get in touch with the use of circuit components and instruments. In addition, the basic circuit has the advantages of simple structure and low implementation cost.

The multifunctional teaching circuit module allows the basic part of the "Circuit Fundamentals" course to no longer remain at the explanation of theoretical concepts, and allows students to no longer be confused about the derivation and verification of formulas and the analysis process of circuit diagrams. Instead, it allows students to learn and operate in the actual operation process, deepening their understanding of theoretical knowledge. At the same time, it also greatly stimulates students' curiosity and improves their hands-on ability.