Schematics

Owned by Jack Christensen
Last updated: Apr 18, 2022
3 min read

Schematics are first and foremost a communication tool. Don’t try to make things as compact as possible, aim for understandability at a glance.

Common Errors

Expand each point for more detailed information.

PDFs are useful for when you need to look at a schematic on a device that doesn’t have KiCad installed. We definitely don’t want to be making critical fixes in the field using an out of date schematic!

This helps keep things understandable and prevents name collisions. Power rails should be kept as global.

Use text fields liberally to explain what each part of the schematic does and how part values were decided upon (eg “from the datasheet” or showing calculations).

This is nitpicky and hard to define but it’s nice when a schematic ‘looks good’. For example,

  • Try to align similar components.

  • Keep some wire (I like 2 grid cells) on either side of intersections / corners. For example,

A readable but not very pretty schematic.
The same schematic, but with some padding at the intersections.

 

We try to place input connectors (data / power) on the left side of the schematic with wires exiting to the right, and output connectors on the right of the schematic with wires coming in from the left.

 

Other Things to Look Out For

Power (All boards):

  • Are all chips driven by the correct voltage?

  • Are all chips correctly grounded?

  • All components: what is the current draw?

    • If this board will be battery powered, what is the battery lifespan?

  • Linear regulators

    • Can they supply the necessary current at the specified voltage difference? See performance curves on datasheet.

    • Is the supply voltage above the dropout voltage?

    • Would a switching regulator be more appropriate? Is the efficiency of the regulator reasonable under the given load? Does it matter?

  • Are there appropriate decoupling caps on all regulators? Check datasheet for value suggestions.

  • Is power actually connected to the board? (There should be a connector coming in that supplies power).

 

Logic & Communication:

  • Are the logic levels of all communicating devices compatible? If not, make sure there’s an appropriate logic level shifter.

  • Voltage dividers: check that resistor values work out for the desired voltage.

  • Are I2C lines pulled up with an appropriate resistor?

  • Do reset pins need to be tied anywhere?

 

Schematic Misc:

  • Do all components have annotations? (R1, C3, etc)

  • Are the proper power symbols (GND, +5V) being used rather than global labels?

  • Are NC pins marked as NC, and not grounded or connected to other crap?

  • Are all non-generic components labeled with their part number?