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RULES.md

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NOWAE - KiCad6 Schematic Symbols Design Rules

Ispired by Library Conventions. This document contains our rules to design schematic symbols and is more or less the same of KiCad Conventions.

Symbol libraries files

Symbol libraries are individual .kicad_sym files. Symbol library names must be defined based on the priority list below, with each element separated by the underscore character:

  • Function (e.g. Sensor, Amplifier, MCU)
  • Sub-function (e.g. Temperature, CurrentSense)
  • Manufacturer name (e.g. Atmel, Infineon)
  • Symbol series name (e.g. PIC24, STM32)
  • Extra library descriptors

Symbol name

  • General symbol naming guidelines

    • Library naming should not be duplicated in symbol name
    • If symbol with same name exists for multiple manufacturers, the manufacturer name is written first
    • Fully specified symbols are named based on the manufacturer part number

  • Non-functional variations in part number should be replaced with wildcard.

  • Separate symbol must be drawn for each footprint: where parts are available in multiple footprint options, a separate symbol must be drawn for each footprint.

General symbol requirements

  • Origin is centered on the middle of the symbol.

  • Text fields should use a common text size of 1.27mm (pin name, pin number, value, reference, footprint, datasheet).

  • Symbol outline body must have a line width of 0.254mm.

  • Symbols with complex functionality may incorporate simple functional diagrams.

  • Pin connection points must be placed outside of the symbol

  • For IC components with exposed pads, the number of the exposed pad should start one greater than the pin-count of the footprint.

  • For symbols with multiple units that are drawn separately, where the units share common power pins, the power pins must be added to the first part (A).

  • Footprint field position: X=0 Y=1.27mm

  • Datasheet field position: X=0 Y=-1.27mm

Pin requirements

  • Using a 2.54mm grid, pin origin must lie on a grid node (IEC-60617),

  • Pins should have a length of at least 2.54mm

  • Pin numbers must be unique (no two pins may have the same number)

  • Where possible, pins should be grouped by similar function, rather than by their physical location on the associated footprint.

  • Pin Electrical type should be set to match the appropriate pin function.

  • Pins not connected on the footprint may be omitted from the symbol.

  • Active low pins should be designated using a bar above the symbol name.

Footprint Association

  • Symbols with a default footprint link to a valid footprint file.

Metadata

Component Reference Designator (RefDes)

Designator Component Type
BT Battery
C Capacitor
D Diode
DL Diode LED
F Fuse
FB Ferrite bead
JP Jumper
K Relay
L Inductor
M Motor
P Connector
Q Transistor
R Resistor
SW Switch
T Transformer
TP Test point
U Integrated Circuit
Y Crystal/Oscillator
Z Zener diode

Symbol metadata fields

  • Symbol and alias fields and metadata filled out as required:
    • Reference field is selected appropriately for the symbol and is visible,
    • Value field contains the name of the symbol and is visible
    • Footprint field contains footprint link for fully specified symbols and must be invisible
    • Datasheet entry is filled out, and is invisible
    • TODO

Special Symbols

  • Power flag symbols are special symbols in KiCad, used to designate global nets. These symbols use a special RefDes value to indicate that they must be considered as global power flags. Label dimension should be 1.27mm