When encountering some small objects, or encountering electronic products without drawings, you need to draw the circuit schematic according to the real thing.
There are the following points:
1. Select components such as integrated circuits, transformers, transistors, etc., which are bulky, have many pins and play a major role in the circuit, and then draw from the selected reference pins to reduce errors.
2. If the component number (such as VD870, R330, C466, etc.) is marked on the PCB, since these serial numbers have specific rules, the components with the same Arabic numerals after the English alphabet are the same functional unit, so the drawing should be used. Correctly distinguishing the components of the same functional unit is the basis of the drawing layout.
3. If the serial number of the component is not marked on the printed board, it is best to number the component yourself for easy analysis and proofreading. When designing printed circuit board components, the manufacturer generally arranges the components of the same functional unit relatively in order to minimize the copper foil routing. Once you find a device that has a core function, you can find other components of the same functional unit as long as you can find it.
4. Correctly distinguish the ground, power and signal lines of the printed board. Taking the power supply circuit as an example, the negative terminal of the rectifier connected to the secondary of the power transformer is the positive pole of the power supply, and a large-capacity filter capacitor is generally connected between the ground and the ground, and the capacitor casing has a polarity mark. The power and ground lines can also be found from the three-terminal regulator pins. When the factory is wiring the printed circuit board, in order to prevent self-excitation and anti-interference, the ground copper foil is generally set to the widest (high-frequency circuits often have large-area grounded copper foil), the power supply copper foil is second, and the signal copper is used. The foil is the narrowest. In addition, in electronic products with both analog and digital circuits, the printed boards often separate their ground lines to form an independent grounding grid, which can also be used as a basis for identification and judgment.
5. In order to avoid excessive wiring of the components, the wiring of the circuit diagram is cross-interleaved, resulting in a messy picture, and the power supply and ground lines can be used in a large number of terminal markings and grounding symbols. If there are many components, the unit circuits can be drawn separately and then combined.
6. When drawing a sketch, it is recommended to use transparent tracing paper, and use a multi-color pen to draw the ground wire, power cable, signal wire, components, etc. by color. When modifying, gradually deepen the color to make the drawing visually eye-catching for analysis of the circuit.
7. Proficiency in the basic composition of some unit circuits and classic drawing methods, such as rectifier bridges, voltage regulator circuits and op amps, digital integrated circuits. These unit circuits are directly drawn to form a frame of the circuit diagram, which can improve the drawing efficiency.
8. When drawing a circuit diagram, you should find a circuit diagram of a similar product as much as possible for reference, which will do more with less.
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