How to Use Protel99se to design ElectronIC Clock PCB

In view of the development trend of modern electronic products, the function of circuit board has more and more obvious influence on the performance of the entire electronic products. Therefore, it is very important to design a PCB that meets the process requirements and meets the normal working performance of the product.

Based on the author's years of experience in teaching and research of electronic courses, combined with the development of single chip microcomputer and the design of circuit board, this paper will specifically describe the important steps and precautions in the design of electronic clock circuit board, a typical product of single chip microcomputer, developed by Protel99se software.

1. Precautions and steps for designing circuit schematic diagram with Protel99se software

The schematic diagram is the most basic basis for realizing circuit functions, and it reflects the electrical connection relationship of electronIC components. In the process of electronic product design, the drawing of schematic diagram is the basis of drawing PCB. The schematic diagram is also the basis for engineering technicians to install and debug products. Therefore, in the process of schematIC design and drawing, the drawing steps and process requirements of schematic must be strictly followed. In the process of drawing the schematic diagram, the basic process requirements such as top-down, left to right, and signal flow direction shall be strictly followed. The components shall be arranged according to the functional modules of the circuit. All connections shall be structured as much as possible. The overall drawing shall be complete in structure, beautiful and readable. For the schematic diagram of more complex products, the hierarchical circuit design thinking can be adopted. In this way, the circuit structure 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, the overall circuit schematic diagram is composed of three sub circuits: the single-chip control circuit, the time display circuit, the date and temperature display circuit. 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 mode of devices in the circuit schematic diagram.

2. Proper package definition and electrical rule inspection for components

component packaging refers to the outer frame and solder joint position indicated by the component placed 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, each component is properly defined as a package according to the actual requirements. In general, the common standard packaging libraries provided in software can meet the design requirements of general products. In modern PCB design and development enterprises, there is generally a standard packaging library built by the company itself.

PCB designers are required to be familiar with the packaging forms of common devices.

For uncertain packaging, actual measurement and self built packaging can be adopted to solve the problem. The form of packaging directly determines the installability of the circuit board, so it must be carefully analyzed and treated when defining.

The final step of schematic design is to check the electrical rules. The software automatically analyzes whether there are multiple network names for the same network in the circuit schematic diagram; Whether there is an input signal hanging in the air; Whether there are errors such as duplicate names of components that do not conform to electrical rules. It should be emphasized here that the inspection of electrical rules cannot replace the verification of the correctness of schematic drawing. The correctness of schematic diagram requires skilLED drawing skills and a high sense of responsibility.

3 Manually lay out all components in the electronic clock printed board

In the layout of electronic clock PCB components, the first thing to be determined is the location of the year, month, day, week, room temperature, and temperature. In this way, the display of the nixie tube can be easily understood. Secondly, considering the placement of nixie tubes at each corresponding position, we must pay attention to the corresponding relationship with the MARKed Chinese characters in this process, so as not to cause display confusion.

On this basis, the positions of the four LEDs can be determined. The four LEDs are designed to display the clock hours, minutes and seconds. The positions must be placed accurately, neatly and beautifully. Then you can determine the location of each interface, and then consider the location of special components such as temperature sensors, relays, etc. Determine the position of the single chip microcomputer and each component constituting the minimum system of the single chip microcomputer, and finally consider other components. The overall layout requires that the performance of normal operation, the aesthetics of the overall PCB, and the Layout of components conform to the modular design idea should be considered.

The rationality of the manual layout and the manufacturability directly determine the performance of the printed circuit board and the direction of the copper film line on the printed circuit board. As a PCB developer, you must accumulate layout experience in the actual engineering design, and summarize the ideas and methods of layout.

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 the wiring function of AI supporting 32 layer PCB. When the automatic routing function of the application software is used for routing, the rules of automatic routing must be set first to enable the software to complete automatic routing under the established rules.

Protel99se supports the setting of multiple utility rules such as safe distance, cabling angle, cabling layer, cabling topology technology, and line width. In the process of use, reasonable settings must be made according to the design requirements and the actual situation, and local adjustments must be made according to the wiring effect. After the automatic wiring is completed, the designer also needs to make local adjustments and modifications to the PCB, add necessary annotation and other work to ensure the realization of the PCB function.

5 Conclusion

As a typical single chip microcomputer product, electronic clock circuit has certain complexity and comprehensiveness. In the process of development and design, the design idea and method of hierarchical circuit schematic diagram, the definition of each component package in the circuit board and the inspection of electrical rules of schematic diagram are extensively involved.

In the PCB design part of PCB manufacturers, the general principles of manual layout and automatic routing are mainly discussed and analyzed, which has certain guiding significance and demonstration role for the PCB design of general electronic products.