Feature: Embedded design
Figure 1: PCB layout of the Arduino UNO R4 Minima
standalone applications, educational environments or projects where wired connectivity (via USB) suffices. Despite its minimalist designation, the R4 Minima is far from basic: it delivers a robust feature set in a compact, UNO-compatible footprint, making it a compelling upgrade path for users transitioning from older Arduino models. Figure 1 shows the Arduino UNO R4 PCB layout. Te PCB
footpath and the placement of the headers on the PCB are the same as the UNO R3. In the centre of the PCB is the RA4M1 microcontroller. On the leſt-hand side of the PCB, you can see the reset button, USB-C connector for connecting to a PC, and the barrel connector for supplying external power. At the far right of the PCB, you can see the 6-pin ICSP pins
(SPI) and the 10-pin SWD/JTAG pins. An on-board LED is connected to port 13 as in UNO R3. Additionally, yellow LEDs are connected to the serial TX and RX pins to indicate serial data transmission, a green LED indicates power to the board, and a yellow LED indicates the state of the SCK pin. Te soſtware ecosystem surrounding the Arduino R4 series has
also been updated to support its advanced hardware. Te boards are fully compatible with the Arduino IDE (both desktop and Web Editor), and benefit from ongoing support in the Arduino CLI and third-party development environments like PlatformIO. Libraries have been updated or newly developed to take advantage of the DAC, op-amp and wireless features, ensuring that users can quickly begin prototyping without needing to dive into low-level register manipulation. Additionally, the R4 Wi-Fi’s wireless capabilities are accessible through high-level APIs, abstracting much of the complexity of Wi-Fi and Bluetooth protocols and enabling rapid development of connected applications.
32 December 2025/January 2026
www.electronicsworld.co.uk From a soſtware architecture perspective, the availability of
interrupt priority levels and nested vectored interrupts (NVIC) means systems can be scaled intelligently using pre-emptive multi-tasking techniques. You can design schedulers with task preemption, context preservation and independent timer allocation – features far more complex to implement on the R3’s AVR core.
Transitioning from UNO R3 to R4 Migrating existing projects involves both hardware and soſtware considerations: Soſtware: • Code portability: Arduino core abstracts most functions, but direct register manipulations will differ.
• Timing mechanisms: ARM timers and clock scaling are different and require adjusted delay logic.
• Interrupt handling: Vector naming and nesting behaviour changes; NVIC offers priority management.
• Compiler toolchain: ARM-GCC introduces different optimisation flags and memory models
Hardware: • GPIO mapping: Maintains the same pinout, simplifying shield reuse.
• Logic levels: Maintains 5V tolerance. However, the source and sink currents of the UNO R4 are rather limited.
• Form Factor: No physical changes required – enclosures and mounts remain valid.
Example project: Sinewave generator In this project, the UNO R4 (Minima or Wi-Fi) is programmed
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