In view of the development trend of modern Electronic products, the function of the circuit board has an increasingly obvious influence on the performance of the entire electronic product. Therefore, it is very important to design a circuit board that meets the process requirements and meets the normal working performance of the product.
Based on the author’s many years of experience in teaching and research in electronics majors, combined with the development of single-chip microcomputers and circuit board design, this paper will specifically describe the important steps and precautions of using Protel99se software to develop electronic clock circuit boards for typical products of single-chip microcomputers.
1 Notes and steps for using Protel99se software to design circuit schematics
The schematic diagram is the most basic basis for realizing the function of the circuit, and the circuit schematic diagram reflects the electrical connection relationship of each electronic component. In the design process of electronic products, the drawing of schematic diagrams is the basis for drawing PCBs. The schematic diagram is also the basis for the engineering and technical personnel to install and debug the product. Therefore, in the design and drawing process of the schematic diagram, the drawing steps and process requirements of the schematic diagram must be strictly followed. In the process of drawing the schematic diagram, it is necessary to strictly follow the basic process requirements such as top-down, left-to-right, and signal flow. The layout of components is carried out according to the functional modules of the circuit. All connections should be structured as much as possible. The overall drawing requires a complete structure, beautiful and easy to read. For the schematic diagrams of more complex products, the design thinking of hierarchical circuits can be adopted. In this way, the structure of the circuit is clear and meets the basic requirements of schematic design. In the drawing of the electronic clock schematic diagram, considering the complexity of the circuit, a scheme of the overall circuit schematic diagram composed of three sub-circuits of the single-chip control circuit, the time Display circuit, the date and the temperature Display circuit is adopted in the design. In the sub-circuit, in order to enhance the readability of the schematic diagram and the convenience of wiring, a large number of network labels are used as the electrical connection method of the devices in the circuit schematic diagram. The overall schematic diagram of the designed electronic clock circuit and the time display circuit schematic diagram of one of the sub-circuits are shown in Figure 1 and Figure 2 respectively.
Figure 1 The overall schematic diagram of the electronic clock circuit
Figure 2 Electronic clock sub-circuit time display circuit
2 Appropriate package definition and electrical rule checking for components
Component packaging refers to the placement of components into the frame and solder joint locations indicated on the electronic circuit board. Different components can share the same component package, and the same component can also have different packages. Generally, after the schematic drawing is completed, the appropriate package definition for each component is carried out according to the actual requirements. Generally speaking, the common standard package libraries provided in the software can meet the design requirements of general products. In modern printed board design and development enterprises, there are generally standard packaging libraries built within the company.
The printed board designer is required to be familiar with the packaging forms of common devices.
For uncertain packages, actual measurement and self-built packages can be used to solve them. The form of the package directly determines the mountability of the circuit board, so it must be carefully analyzed and treated with caution when defining it.
The final step in schematic design is electrical rule checking. It is mainly used by the software to automatically analyze whether there are multiple network names in the same network in the circuit schematic diagram; whether there are dangling and unconnected input signals; It should be emphasized here that the checking of electrical rules is not a substitute for verifying that the schematic drawing is correct. The correctness of the schematic requires skilled drawing skills and a high sense of responsibility.
3 Manual layout of all components in the electronic clock printed board
In the layout of electronic clock printed board components, the first thing that needs to be determined is the position of the marked Chinese characters for the year, month, day, week, room temperature, and degree. Only in this way can the display of the digital tube be easy to read. Secondly, considering the placement of the digital tubes in each corresponding position, in this process, we must pay attention to the corresponding relationship with the marked Chinese characters, so as not to cause confusion in the display.
On this basis, the position of the four LEDs can be determined. The four LEDs are designed to display the hours, minutes, and seconds of the clock. The placement must be accurate, neat and beautiful. The location of the various interfaces can then be determined, after which the location of special components such as temperature sensors, relays, etc. can be considered. Determine the position of the single-chip microcomputer and the various components that make up the minimum system of the single-chip microcomputer, and finally consider other components. The overall layout requires consideration of the performance of normal work, the aesthetics of the overall PCB, and the layout of components in line with the modular design concept.
The rationality of the artificial layout and the craftsmanship directly determine the performance of the printed board and the direction of the copper film lines on the printed board. As a printed board developer, you must accumulate layout experience in actual engineering design, and summarize layout ideas and methods.
4 Use the function of software automatic routing to route and adjust the electronic clock PCB
Protel99se has a very complete automatic routing function. It can simulate artificial intelligence to support the routing function of 32-layer circuit boards. When applying the automatic routing function of the software for routing, the rules of automatic routing should be set first, so that the software can complete the automatic routing under the established rules.
Protel99se supports the setting of many practical rules such as safety distance, wiring angle, wiring layer, wiring topology, and line width. In the process of use, reasonable settings must be made according to design requirements and actual conditions, and local adjustments must be made according to the effect of wiring. After the automatic routing is completed, the designer also needs to make local adjustments and modifications to the PCB, add necessary annotations and other work to ensure the realization of the function of the circuit board diagram. The completed PCB of the electronic clock circuit board is shown in Figure 3.
Figure 3 The PCB after the automatic wiring of the electronic clock circuit is completed
As a typical single chip product, electronic clock circuit has certain complexity and comprehensiveness. In the process of development and design, the design ideas and design methods of the hierarchical circuit schematic diagram, the definition of each component package in the circuit board, and the inspection of the electrical rules of the schematic diagram are widely involved.
In the PCB design part of the circuit board, the general principles of manual layout and automatic wiring are mainly discussed and analyzed, which has certain guiding significance and demonstration effect for the circuit board design of general electronic products.
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