Understand the circuit diagram

- Jul 18, 2019-

A circuit diagram usually has dozens or even hundreds of components, their wiring cross-sectional, the form of many ends, beginners often do not know from what place to start, how to read it. In fact, the electronic circuit itself has a strong regularity, no matter how complex the circuit, after analysis can be found that it is composed of a few unit circuits. As if children play with building blocks, although there are only a dozen or twenty or thirty blocks, but in the hands of children can be built into dozens or even hundreds of kinds of graphic or three-dimensional models. By the same token, complex circuits, after analysis, can be seen, it is also composed of a few unit circuits. Therefore, as long as beginners first familiar with the commonly used basic unit circuit, and then learn to analyze and decompose the circuit skills, understand the general circuit diagram should be not difficult.

According to the function of the unit circuit can be divided into several categories, each of which has a variety of, all cell circuits are probably hundreds of kinds. Let's pick the most commonly used basic cell circuits to introduce.

Let's start with the power circuit. Electronic technology enthusiasts like to engage in some small electronic production, not only in practice to improve their own technical level and hands-on ability, but also can achieve real results. When we have identified a small production project, the first thing to understand its circuit diagram, which is the premise of small production.

What is a circuit diagram

Circuit diagrams, also known as circuit schematics, are drawings that reflect the electrical connections of components in electronic devices. Circuit diagrams consist of abstract characters, according to certain rules. Through the analysis and research of circuit diagrams, we can understand the circuit structure and working principle of electronic equipment. Therefore, understanding circuit diagram is an important part of learning electronic technology, is the premise of electronic production or maintenance.

The circuit because of which elements are composed of

A complete circuit diagram is made up of a number of elements, including graphic symbols, literal symbols, lines, and annotated characters. Below we illustrate further with the example of the wireless microphone road map shown in Figure 1.

1. Graphic symbol

A graphic symbol is the body that makes up a circuit diagram. Figure 1 shows the various graphical symbols representing the components that make up the wireless microphone. For example, a small rectangle 074125dpiwp16imfnpm1ferepresents a resistor, two short bars 074125e08u63rmrpiiainprepresent capacitors, a continuous semi-circular 074125ytxa5uxd35rne7berepresents a inductor, etc. The circuit structure of the wireless microphone can be reflected by connecting the graphic symbols of each component by wire, that is, the circuit diagram that constitutes the wireless phone.


2. Text symbols

Text symbols are an important part of the circuit diagram.

In order to further emphasize the nature of graphical symbols, but also to analyze, understand, and elaborate The convenience of circuit diagram, next to the graphic symbol of each component, is marked with the text symbol of the component.

For example, "R" means resistor, "C" means an electric container, "L" means inductor, "VT" means transistor, "IC" means integrated circuit, etc.

3.  Annotated characters

Annotative characters are also an important part of the diagram that makes up the component and is used to illustrate the numerical size or specific model of the component. For example, in Figure 1, we can see through the annotation characters that the value of resistor R1 is 3.3k?

The drawing rules of circuit diagrams

In addition to providing uniform graphic symbols and text symbols, circuit diagrams also follow certain rules of drawing. Understanding and mastering the general drawing regulations of circuit diagrams is essential for understanding circuit diagrams.

1. Signal processing process direction of the circuit diagram

The direction of the signal processing process in the circuit diagram is generally from left to right, and the individual cell circuits that will process the signal in succession are arranged from left to right, which is the most common form of arrangement. For example, the wireless microphone circuit diagram shown in Figure 1, from left to right, is a cell circuit such as voice signal reception (BM), audio release (VT), high frequency oscillation and modulation (IC).

2. Connecting the wires

The connecting wires between the components are represented by solid wires in the circuit diagram. The connection and intersection of the wires are shown in Figure 2, with a dot at the intersection of the two wires in Figure 2(a) indicating that the two wires are connected together. Figure 2 (b) There are no dots at the intersection of the two wires, indicating that the two wires are intersected without connecting. The tinted connection of the wire is shown in Figure 2 (c).


3. Power cord and ground

The power leads are usually arranged above the component and the ground wire is arranged below the component, as shown in Figure 3 (a). Some circuit diagrams do not connect all ground wires together, but instead replace them with isolated ground symbols, as shown in Figure 3 (b), should be understood as all ground symbols are connected together.


Connect the power cord and ground wire as shown in Figure 4.


5. The drawing of integrated circuits

The internal circuits of an integrated circuit - all of which are complex, contain several cell circuits and many components, but are usually viewed only as a component in circuit diagrams, so almost all circuit diagrams do not draw the internal circuits of the integrated circuit, but are represented by a rectangular or triangular block diagram. Integrated amplifiers, voltage comparators and other habits are represented by triangular block diagrams, and other integrated circuits are used to be represented by rectangular block diagrams, as shown in Figure 5. The left side is the input and the right side is the output.


(1) The signal is converted to an electrical signal.

(2) The audio amplification circuit consisting of transistor VT, etc., whose function is to amplify the audio signal output of the BM.

(3) High-frequency oscillation and modulation circuit consisting of integrated circuit IC, which is functioning to produce high frequency carrier signal and complete FM modulation.

Figure 6 shows a diagram of the wireless microphone circuit principle. 

4. Analysis of the circuit working process

Usually the circuit diagram does not draw the integrated release and digital integrated circuit power leads, because this does not affect the analysis of circuit functions, but the analysis of the power circuit and the actual production of its power supply leads can not be forgotten. For example, the integrated circuit IC in Figure 1, actually produced.

Look at the circuit diagram methods and steps

With the above basic knowledge, the circuit diagram can be completely analyzed.

Let's take the wireless microphone circuit diagram shown in Figure 1 as an example to introduce the basic methods and steps for looking at the circuit diagram.

1. Judge the direction of the signal processing process

According to the overall function of the circuit diagram, the signal processing process direction of the circuit diagram can be determined by finding out the total input and the total output end of the whole circuit circle. The function of the wireless microphone is to modulate the voice signal to the high frequency signal to transmit out, in figure 1 circuit diagram, the microphone BM is the total input, antenna W is the total output end. From the total input to the total output is the direction of the signal processing process, and Figure 1 is arranged in a left-to-right direction.

2. Dividing the unit circuit

Generally speaking, transistors, integrated circuits, etc. are the core components of each unit circuit. Therefore, we can use the transistor or integrated circuit and other major meta-devices as a sign, according to the direction of the signal processing process to break down the circuit diagram into several cell circuits, and draw a diagram of the circuit principle block. Block diagrams help us master and analyze circuit diagrams.

Figure 1 circuits can be broken down into 3 cell circuits:

(1) The voice signal reception circuit consisting of the station microphone BM, etc., whose function is to voice the voice

Through the above two-step analysis, we have a basic understanding of the wireless microphone circuit, you can compare the diagram 1 circuit diagram and Figure 6 box diagram, the wireless microphone electrical principle for systematic analysis. The circuit works as follows: after the voice signal is converted to an electrical signal by the station microphone BM, it is entered into the transistor VT base by coupling capacitor C1. R1 is the load resistor of the BM. The transistor VT and other components of the voltage amplifier, the C1 coupled audio signal amplified, by C2 coupling output. R2 is the base resistor and R3 is the collector resistance. Integrated circuit Ic and other components of high-frequency oscillators, oscillating frequency is determined by L, C4 series resonance circuit, C4 is a fine-tuning capacitor, used to regulate the oscillation frequency. C3 is a feedback capacitor. The C2-coupled audio signal makes frequency modulation of the high-frequency oscillation signal, and the FM signal is transmitted by C5 coupling to antenna W.

3. Analysis of DC power supply circuit

The power supply is usually arranged on the right side of the circuit diagram, and the DC power edtheys are arranged from right to left. In Figure 1, the DC operating power supply for the whole electromechanical circuit is a 6V battery, r4, C6 and regulator diode VD constitute a regulator circuit to improve the stability of the circuit operation. S is the power switch.

At this point, the wireless microphone circuit diagram is basically analyzed. Readers can flexibly use the above-mentioned image-viewing knowledge and methods, through practice to continuously improve their own ability to see the picture.