Embedded

SPI to 4x UART Bridge

Expand Your Microcontroller with 4 New Serial Ports Over SPI

If you work with electronics, you know how quickly you can run out of hardware serial (UART) ports. Affordable components like Wi-Fi, Bluetooth, GPS, and cellular modules all require UART connections, but most modern microcontrollers—and even the Raspberry Pi—only offer one or two. Upgrading to a larger chip can mean rewriting your entire codebase.

This expansion board solves that problem by turning a single SPI connection into four fully independent, buffered UART channels.
Key Features

Stackable Design: Need more than four ports? Simply stack a second board to get eight channels, and keep expanding as needed.

Large Buffers: Every UART channel features dedicated 1,000-byte transmit and receive buffers to prevent data loss, even during simultaneous, heavy traffic.

Smart LED Indicators: The onboard LED shifts brightness to show power status, UART activity, and active SPI communication at a glance.

Broad Compatibility: Powered by 3.3V, but features 5V-tolerant SPI and UART RX inputs. The 3.3V TX output works seamlessly with both 3.3V and 5V devices without requiring external level shifters.

RS232 Ready: Easily converts to RS232 levels using a standard MAX2323 chip.

Simple Command Structure

Instead of managing complex registers, the board uses a highly efficient, single-byte command system to control everything. You can check buffer sizes, read/write data blocks, and configure baud rates on the fly.

Supported Baud Rates: 1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200.
What's New in Version 2

The V2 board introduces an updated, lower-profile microcontroller that improves manufacturing reliability, reduces waste, and lowers costs. It remains 100% backward compatible with Version 1.
Software & Support

To get you up and running instantly, an Arduino library and Flowcode component are available. The onboard firmware can also be updated using a PICkit 3.