Even as a six-year-old, my son is great at organizing his toys and personal belongings. At that age, I used to chuck all my possessions into a huge storage box. My son, on the other hand, has a knack for orderliness that borders on obsessive. Although his meticulous attention to detail can be mildly frustrating at times, it means that I can always trust him to keep his play area organized.
In PCB design, you need to exhibit the same level of organization in your schematics document to ensure that any hardware designers inheriting your project can progress with ease. The last thing you want is being constantly harassed by calls and emails because no one can understand your schematics.
Schematic Design Basics
Many electronics design articles discuss PCB layout best practices, like reducing electromagnetic interference (EMI) or high-speed design. But before you can even start routing the first net on a PCB, you have to get the schematics right. Schematics design is, in fact, one of the most overlooked aspects of PCB design.
When you’re starting a hardware design, you probably have a general idea of what the complete circuit should look like. A approach to schematic design is to start by placing the main components, like the microcontroller, memory chips, and special function integrated circuits (IC). Then, you would place the passive components before making connections between components.
The schematic is then exported to the PCB layout, where the respective footprints are populated with the interconnecting nets. A schematic design that generates the correct connections in the PCB seems to be all that matters; but in reality, a schematic design needs to be properly organized to ensure that it's easily understood and reused.
How to Organize Your Schematic Design
Keeping your schematic organized is a combination of habit and the features of the PCB design software that you’re using. Here’s how I normally organize my schematics:
1. Segregate Schematic Sheets by Function
In a simple design with a relatively low component counts, it makes sense to create the whole circuit on a single schematic sheet. But when you’re taking on complicated hardware design where hundreds of components are involved, squeezing everything on a single schematic sheet can be rather overwhelming.
Instead, you may want to create different schematic sheets for different functions like the diagram above. Not only does this make the schematics in the individual sheets more manageable, but they can also be easily reused in new designs.
Schematic documents organized in rows
2. Create a System for Designators
Designators can be a great way to quickly cross-reference components within the schematic. You’ll be glad to have a designator system in place when you’re trying to locate or remove a single capacitor amidst hundreds of components.
In my schematics, designators are built to represent the type of components, the number of the sheets that it belongs to, and the component index within the sheet itself. For example, D0512 represents a diode in the fifth schematic sheet and is the twelfth similar component. For a general overview of the component count, you can also list the range of each component at the bottom of the schematic sheet.
3. Create Subcircuit Separations on Schematic Sheet
Keeping schematics neat and tidy involves more than simply splitting the circuit into separate sheets. Some sheets contain more components and are vastly complicated than others. It always helps to create sub-schematic groups to clearly highlight the different purposes of the schematics.
For example, the “memory” schematic sheet contains circuits that relate to SRAM, FRAM, Flash and SD Card. It’s important to ensure that components related to each memory type are positioned close to each other but sufficiently separated from others.
4. Use Net and Port Labels
The easiest way to represent a physical connection between two pins is to draw a wire connection. In simple schematics, this gives you a complete picture of the circuit with a single glance. But with complex circuits involving hundreds or thousands of nets, using net or port labels is a better option.
It’s a good practice to use netlabels for signal connections within the same schematic sheet and port labels for connections between different sheets, as illustrated in the figure above. It’s also important to use the same punctuation and spelling when repeating labels.
Schematic information with corresponding designators
5. Add Useful Comments
It doesn’t hurt to add comments to the schematic where necessary. Besides basic information like the version, , and date, you may also want to include notes on any design concerns to keep in mind during the PCB prototyping process. Clearly spelling out instructions helps minimize issues for others who may be involved in the design process.
With PCB design, usually you’re not going to be the only one looking at your documents. Being able to manage your information effectively will become a true gift the more involved your design process becomes with the rest of your department and team. Whether it’s easily translatable data formats, or just clearly communicated designators and component information, your schematic can hold a lot of the necessary information for involved parties.
Whether you need to add schematic sheets or include comments, Altium Designer® offers the right tools to simplify your organizational process. Need more help clearing up the mess in your schematic? Talk to an expert at Altium.
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