Introduction
Designing your own PCB is one thing making it modular and AX22 compatible takes it to the next level. The AX22 standard defines a compact 22 × 22 mm modular interface that brings plug-and-play flexibility to your electronics projects. Whether you are building with ESP32, Arduino, or STM32, integrating an AX22 port into your custom PCB allows you to connect a growing ecosystem of sensors, displays, and actuators effortlessly.
In this guide, we will walk through everything you need to know to add an AX22 port to your board from pin assignments and footprint integration to design tips and common pitfalls to avoid.
AX22 MODULE Dimensions
Every AX22 module follows a precise 22 × 22 mm layout, which is where the name “AX22” Axiometa 22×22 Module comes from. This standard size ensures full cross compatibility between modules and development boards.
The PCB features four 2.7 mm mounting holes, one near each corner, with rounded corners of 2 mm radius for easier handling and enclosure fitting. The holes are spaced 18 mm apart, center to center, allowing modules to be securely mounted or stacked in compact configurations.
For electrical connectivity, the module uses two 1×05 headers (2.54 mm pitch) placed 17.78 mm apart, making it breadboard compatible and easy to prototype.
This spacing ensures you can plug the module directly into standard breadboards or AX22-compatible bases without adapters.
Silkscreen design follows a simple convention:
- Top silkscreen is used for pin labeling and logo
- Bottom silkscreen is used for a module name, and SKU number
- All text uses DM Sans 9 pt for consistency across the ecosystem.
It is worth noting that silkscreen positioning may vary slightly depending on through-hole component placement a small trade-off for mechanical compatibility across different assembly types.
Figure 1. AX22 Module Dimensions
AX22 Pinout
The AX22 interface is built to be flexible, MCU-agnostic, and firmware-friendly, enabling a single port to support analog, digital, UART, SPI, and I²C without redesigning your board. Each module connects through two 1×5 headers, with power, GPIO, and serial buses clearly structured across the left and right sides.
Left Header (Power & GPIO)
| Pin | Name | Primary Use | Alternate Functions |
|---|---|---|---|
| 1 | GND | Ground reference | – |
| 2 | 3.3 V | Power input for the module | – |
| 3 | GPIO 0 | Digital I/O | ADC input |
| 4 | GPIO 1 | Digital I/O | PWM, SPI-CS, UART-TX |
| 5 | GPIO 2 | Digital I/O | UART-RX |
Right Header (Dedicated Serial Buses)
| Pin | Name | Primary Use | Alternate Functions |
|---|---|---|---|
| 1 | MOSI | SPI data (Master Out, Slave In) | – |
| 2 | MISO | SPI data (Master In, Slave Out) | – |
| 3 | SCK | SPI clock | – |
| 4 | SDA | I²C data | – |
| 5 | SCL | I²C clock | – |
Figure 2. AX22 Port Pinout
AX22 Port Dimensions & Integration
AX22 ports can be implemented on a PCB in two primary ways, depending on your assembly method and mechanical requirements. Both versions maintain full pin compatibility, but each offers different advantages when it comes to durability, manufacturing, and how the module is mounted.
Through-Hole AX22 Port （Left）
The through-hole version is the most common and beginner-friendly option. It uses standard 01x05 2.54 mm pin headers and provides strong mechanical anchoring to the PCB.
SMD AX22 Port （Right）
The SMD version is designed for compact products and automated assembly lines where space and manufacturing speed matter. To maintain rigidity, we recommend using 02×05 2.54 mm pin headers for each side rather than single-row headers.
NOTE: While SMD single-row headers are possible, they are more prone to mechanical bending sideways, and from our experience pad tearing. The 02×05 format increases bonding area on both sides and ensures the connector remains secure over long-term use.
Figure 3. AX22 Ports. a) Through hole b) SMD Variant.
Placement Recommendation:
For the best mechanical fit and usability, AX22 ports should ideally be positioned along the edge of the PCB. This allows modules with forward-facing connectors—such as relays, StemmaQT/Qwiic ports, audio jacks, or any module with external I/O—to extend past the board without mechanical interference.
If edge placement is not possible or not required for your design, a good alternative is to leave at least twice the module’s 22 mm length (≈44 mm) of free space in front of the connector. This ensures clearance for modules that extend forward, such as IPS displays or sliding potentiometers. These longer-front modules are less common, but providing this allowance keeps your design compatible with the full AX22 ecosystem.
Ultimately, it is up to the designer to evaluate the intended use case and choose the placement that best fits the product’s form factor, mechanical constraints, and expected module types.
NOTE: Mounting holes for AX22 ports are optional and can be included or omitted depending on your mechanical needs. Many designs will not require them, while others may benefit from the additional stability when using heavier or plug-in modules.
Figure 4. AX22 Ports facing away.
AX22 KiCad Template Project
To make integration as straightforward as possible, a ready-to-use KiCad reference project is available for anyone designing AX22-compatible hardware. This project includes both the schematic symbols and PCB footprints required to implement AX22 ports and modules correctly, allowing you to start building immediately without recreating the standard from scratch.
DOWNLOAD AX22 KiCad Template
Figure 5. AX22 Template Ports in KiCad
Summary
The AX22 standard provides a unified 22 × 22 mm module format with a consistent dual-header pin layout, making it easy to design interchangeable electronic modules that work across different PCBs, development boards, and prototypes. With fixed mechanical dimensions, optional mounting holes, and clear separation of power/GPIO on the left and SPI/I²C on the right, AX22 simplifies routing, maintains signal integrity, and ensures electrical compatibility. Ports can be implemented as through-hole or SMD, placed on the PCB edge or with sufficient clearance, depending on the product’s needs. A downloadable KiCad reference project with schematics, footprints, and a module template is available to help designers integrate AX22 ports or build their own modules quickly and correctly.