Ex1-backplane

Setup

Git Large File Storage

Install git-lfs to fetch datasheet PDFs and other large files.

KiCad Libraries

TODO

KiCad Style Guide

TODO

Schematics

Naming

• Group decoupling caps with ICs (so U1 has cap C1, etc)
• Keep references contiguous for related parts (R10+R11, not R23+R14)
• Always prefer ~NET to nNET/etc
• Always prefer NET+/NET- to NET_P/NET_N/etc

Hierarchy

• Use hierarchical schematics for large functional blocks
• Always prefer hierarchical pins to global net names

Passives

• Prefer resistor arrays on proto boards (smaller component count)
• Use R_Small and C_Small to keep schematic smaller
• Always use the Capacitor_SMD_RD and Resistor_SMD_RD footprints
• Prefer 0603 for NFF boards and 0402 for FF boards

Connectors

I2C

• Follow the SparkFun Qwiic standard
  • Right-angle connector: JST SM04B-SRSS-TB
  • Vertical connector: JST BM04B-SRSS-TB
  • Pin order:
    1. GND (black)
    2. 3V3 (red)
    3. SDA (blue)
    4. SCL (yellow)
• ~INT can be exposed by a 2 pos 2.54mm header
  • Pin order:
    1. ~INT
    2. GND

UART

• Use the same Qwiic connector as for I2C
  • Pin order:
    1. GND (black)
    2. 3V3 (red)
    3. TX (blue)
    4. RX (yellow)

USB

• Prefer JAE DX07B024JJR1500 mid-mount USB-C 3.1 connector
• TODO(benvanik): test JAE DX07W024JA1R1000 for waterproof use

Board-to-Board

• Samtech Q Strip-series QSE/QTE
  • QSE-020-01-F-D-A 40-pos receptacle
  • QTE-020-01-F-D-A 40-pos header

PCBs

Units

• Prefer metric
• Larger components aligned to 0.5mm grid
• Smaller components/traces aligned to 0.25mm grid

Silkscreen

• Use 1x1mm / 0.15mm font (smaller may be unreadable from JLCPCB)
• Align reference labels to footprint boundary when possible
• Hide reference labels for mounting holes and other misc footprints
• Prefer human-readable labels instead of references for major IO ports

Physical Design

• Prefer M2 grounded mounting holes with vias (or M3 for larger boards)
• Use 90deg arcs with a 0.55mm radius for board corners
• Include several 0.5mm fiducials
• Avoid through-hole components where possible (prefer SMD pin headers/etc)
• Use 2.54mm pin headers for NFF boards (jumpers/etc)

Layer Stackup

(from Controlling Radiated EMI Through PCB Stack-up)

4 Layers

1. Signal
2. GND
3. Power
4. Signal

6 Layers

1. Signal
2. GND
3. Signal
4. Power
5. GND
6. Signal

8 Layers

1. Signal
2. GND
3. Signal
4. Power
5. GND
6. Signal
7. GND
8. Signal