Embedded-cHow-ToBeginner · 4 min read

How to Design Raspberry Pi HAT PCB: Step-by-Step Guide

To design a Raspberry Pi HAT PCB, start by using the official 40-pin GPIO header footprint and follow the HAT mechanical dimensions from Raspberry Pi Foundation. Create the schematic with required components, route signals carefully, and ensure compliance with the EEPROM specification if your HAT needs auto-detection.

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Syntax

Designing a Raspberry Pi HAT PCB involves these key parts:

GPIO Header Footprint: Use the official 40-pin GPIO connector footprint matching Raspberry Pi.
Mechanical Dimensions: Follow Raspberry Pi HAT size and mounting hole specs for proper fit.
Schematic: Draw the circuit with components connected to GPIO pins.
PCB Layout: Route traces, place components, and add mounting holes.
EEPROM: Optional chip for HAT identification by Raspberry Pi.

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GPIO Header Footprint: 2x20 pins, 2.54mm pitch
Mounting Holes: 4x M2.5 holes at 65mm x 56.5mm spacing
EEPROM: 24C32 or 24C64 I2C EEPROM connected to pins 27 (SDA) and 28 (SCL)

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Example

This example shows a simple Raspberry Pi HAT schematic snippet with GPIO header and EEPROM connections.

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E1: GPIO Header 40-pin
Pins 27 (SDA) and 28 (SCL) connected to EEPROM
EEPROM: 24C32 I2C EEPROM
VCC and GND connected properly
Mounting holes placed at corners

Output

Schematic includes GPIO header with pins 27 and 28 connected to EEPROM SDA and SCL lines, power and ground connected, and mounting holes positioned correctly.

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Common Pitfalls

Common mistakes when designing Raspberry Pi HAT PCBs include:

Using incorrect GPIO header footprint causing poor connection.
Ignoring mechanical dimensions leading to misfit on Raspberry Pi.
Forgetting to add the EEPROM or wiring it incorrectly, so the Pi cannot detect the HAT.
Poor trace routing causing signal interference or shorts.
Not placing mounting holes in the right spots, risking physical damage.

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Wrong: Using 2x19 header instead of 2x20
Right: Use official 2x20 40-pin header footprint

Wrong: EEPROM missing or not connected to pins 27 and 28
Right: Connect EEPROM SDA to pin 27 and SCL to pin 28 with pull-up resistors

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Quick Reference

Aspect	Details
GPIO Header	40-pin, 2x20, 2.54mm pitch, official footprint
Mechanical Size	65mm x 56.5mm with 4 mounting holes (M2.5)
EEPROM	24C32 or 24C64 I2C EEPROM on pins 27 (SDA) and 28 (SCL)
Power	3.3V and 5V pins connected as needed
Mounting Holes	4 holes at corners for secure attachment

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Key Takeaways

Use the official 40-pin GPIO header footprint to ensure compatibility.

Follow Raspberry Pi HAT mechanical dimensions for proper fit and mounting.

Include and correctly wire the EEPROM for automatic HAT detection.

Route PCB traces carefully to avoid signal issues and shorts.

Place mounting holes accurately to secure the HAT safely.