System Diagrams / Schematics

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Most designs start with a sketch of some type– be it on a napkin, whiteboard, a quick CAD model, or scribbled in the air. When dealing with designs that involve multiple separately developed components, a system diagram (sometimes referred to interchangeably with system architecture or system schematic) becomes valuable.

A system diagram helps break the problem into manageable and manufacturable chunks, providing a visual guide for the development.

Tools and Resources

For anyone venturing into systems engineering, two standout resources are the NASA System Design Handbook and the MIT OCW course. These provide a solid foundation for understanding the principles and practices of systems design.

The MIT OCW course has some excellent walk-throughs of the brainstorming and factoring process.

Categories of System Diagrams

Sketch

The initial step in any design is often a sketch. This is a rough, informal drawing used to start discussions and brainstorm ideas. It’s typically created using tools like Inkscape, Libreoffice Draw / Microsoft Publisher, or even Libreoffice Impress / Microsoft PowerPoint.

A sketch doesn’t need to be polished. Its value lies in its ability to quickly convey concepts and guide conversation. If the mechanical or aesthetic design is crucial, you might use 2D views from mechanical CAD software like FreeCAD to show proposed system decompositions.

Design Cartoon

Once you have a rough idea from the sketch, you can represent it in a design cartoon. This is a more detailed diagram that represents the system with a mix of high-level concepts and specific details. Include notes, topics to discuss and research, and highlight any possible issues visually.

It’s more complex than a sketch but less detailed than a full schematic. It serves as a bridge between the abstract and the technical. The component boundaries, physical details, and interconnects are important to fully detail to make sure no sections are missed that would change the system factoring.

© Canon Inc. All rights reserved.

Interface Control Document

Following the creation of design cartoons, you typically document the interface details of each component in an Interface Control Document (ICD). This document describes how components interact, ensuring clarity and consistency in integration.

System Schematic

Finally, the system schematic is a comprehensive technical diagram. It includes progressively increasing levels of detail, ideally maintaining a consistent amount of information at each layer. The schematic should connect the ICDs into a cohesive representation, leaving no connections ignored. This is a technical document for detailed design and analysis.

Using KiCAD’s Eeschema for System Diagrams

I have been using KiCADs schematic editor (eeschema) to draw both the system cartoons and the system schematics. I will make a library of symbols for each project and draw subsections for the cartoons. For the schematics I’ll use hierachical schematics for each section.

As system diagrams are essentially a schematic or wiring diagram the included tools are a natural fit. It’s a natural tool as an electronics designer but that shouldn’t be seen as a barrier of entry to other users!

# FIXME make a Canon schematic design! Example of a system design cartoon using KiCAD.

KiCAD’s eeschema is a versatile tool not just for designing traditional circuit schematics but also for creating various types of system diagrams, including sketches, design cartoons, and detailed schematics. Here’s how you can leverage eeschema effectively:

Creating System Cartoons

  1. Use Hierarchical Sheets: Utilize hierarchical sheets to break down your system into manageable sections. This allows you to create a high-level overview and then dive into more detailed sections as needed. Hierarchical sheets are especially useful for representing subsystems or modular components in a clean and organized manner.

  2. Create Custom Symbols: For a design cartoon, you might need symbols that are not available in the default library. Use the symbol editor in KiCAD to create custom symbols that represent different components or abstract blocks in your system.

  3. Add Annotations and Notes: Include text boxes to add notes or annotations directly onto your diagram. This can be useful for capturing high-level ideas, design considerations, or areas that need further development. Use the “Place Text” tool for this purpose.

  4. Organize with Colors and Layers: To enhance clarity, use colors and layers to differentiate between various types of connections or components. This can help make your design cartoon more visually intuitive.

Transitioning to Detailed Schematics

  1. Define Component Libraries: As you transition from a design cartoon to a detailed schematic, ensure that you have defined and organized your component libraries. eeschema allows you to manage and import symbols, footprints, and component data, making it easier to create a detailed and accurate schematic.

  2. Create and Connect Symbols: Place symbols from your libraries onto the schematic sheet and connect them using wires. For complex systems, consider using hierarchical sheets to manage connections between different parts of your design.

  3. Utilize Electrical Rules Check (ERC): Run the ERC tool to identify any potential issues or errors in your schematic. This ensures that all connections are valid and that the design meets electrical design standards.

  4. Annotate and Document: Use eeschema’s annotation tools to label components and nets systematically. This helps in maintaining clarity and consistency throughout the schematic. Additionally, generate documentation such as Bill of Materials (BoM) and netlists directly from KiCAD.

  5. Version Control and Collaboration: KiCAD supports version control tools, allowing you to manage different versions of your schematic and collaborate with team members. Use version control to keep track of changes and ensure that everyone is working with the most up-to-date design.

Tips for Effective Use

  • Keep It Organized: Use hierarchical sheets and consistent naming conventions to keep your schematic organized and easy to navigate. This is particularly important for complex designs with multiple interconnected components.

  • Leverage Templates: Create or use existing templates for common design patterns or systems. This can speed up the design process and ensure consistency across different projects.

  • Regular Backups: Regularly save and backup your work to avoid losing progress. KiCAD projects can be complex, and backups ensure that you don’t lose important design data.

  • Explore Community Resources: The KiCAD community is active and full of resources. Explore forums, tutorials, and example projects to learn new techniques and best practices for using eeschema.

Tools for Creating System Diagrams

While KiCAD’s schematic editor (eeschema) is a great tool for both system cartoons and schematics, it’s not the only option.

Closed source tools include:

Resources & Links