Keepin' It Real-Time

Before starting on a new embedded electronics project, one of the first decisions you'll need to make is choosing between a microcontroller and a single-board computer. To determine what you need, you’ll have to ask yourself a few questions. Do you need a full operating system, perhaps with multitasking and a desktop interface? What are the power constraints for the project? Do you need real-time precision?

The choice is usually clear, but sometimes the answer falls somewhere between the two options. If you need a multitasking operating system and real-time code execution, things get more complicated. Fortunately, Redditor Machinehum just built something that makes this situation easier to deal with. It is a Raspberry Pi HAT named RPI RTShield. It adds an RP2350 microcontroller and a few other goodies to a Raspberry Pi. It is something like an Arduino UNO Q for the Raspberry Pi ecosystem.

You've got perfect timing

The RTShield is designed to act as a dedicated real-time companion for a Raspberry Pi, offloading time-critical tasks from Linux while still maintaining a connection between the two systems. At the core of the HAT is the RP2350 microcontroller, which communicates with the Raspberry Pi over a UART serial link. Rather than wiring sensors and external hardware to the Raspberry Pi, all sensor connections are routed through the microcontroller, allowing deterministic control and monitoring that would be difficult to guarantee under a multitasking operating system.

Users get eight 12-bit analog inputs operating from 0 to 3.3 volts, four 12-bit analog outputs, two relays for dry-contact switching, three status LEDs, configuration DIP switches, and Arduino-compatible pin headers for expansion. This makes the board suitable for robotics, industrial monitoring, automation projects, and other applications that need both Linux-level software capabilities and microcontroller-style hardware control.

Who needs an external programmer anyway?

The RP2350 can be programmed directly from the Raspberry Pi using OpenOCD and GPIO-connected SWD signals. This eliminates the need for a separate programming adapter and streamlines firmware development. The initial installation consists of cloning the project repository, installing the required build tools, compiling the firmware, flashing the microcontroller, and installing the accompanying software package.

To simplify communication with the hardware, Machinehum also created a Python module that runs under Linux on the Raspberry Pi. With only a few lines of code, users can read analog inputs, drive digital outputs, control relays, toggle LEDs, and monitor switch states. This allows developers to combine high-level Python applications with low-level real-time hardware control without needing to constantly switch between environments.

The project is currently open source and available under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 license. Full details are available in RTShield’s GitHub repository.