The circuit diagram in the paper can't be read directly. The circuit diagram must be drawn with protel, and do not take screenshots directly. It is not clear to enlarge it after pasting. It is recommended to generate a pdf and take a screenshot after enlargement. A circuit diagram refers to a diagram showing circuit connections with symbols of circuit elements. It is a kind of principle layout diagram, which uses physically and electrically standardized symbols to express the relationship between components and equipment to meet the needs of research and engineering planning. The working principle between components can be known from the circuit diagram, which provides a planning scheme for analyzing performance and installing electronic and electrical products. When designing the circuit, engineers can finish it on paper or computer calmly, and then install it after confirming it is perfect. Improve and fix errors through debugging until success.