RA4M1 Nano Board From David Johnson-Davies Shrinks the UNO R4 Minima to a Breadboard-Friendly Size

The most welcomed feature when Arduino introduced the UNO R4 boards at Arduino Day 2023 was that its new microcontroller, a Renesas RA4M1, was 32-bit and 5-volt logic tolerant! But some people asked, what about the breadboard-friendly Nano? Until now, there has not been an option. David Johnson-Davies of Technoblogy created the RA4M1 Nano Board, which puts the R4AM1 chip on a PCB that is highly compatible with the UNO R4 Minima Arduino board package and pin-compatible with existing Nano boards.

Even though the RA4M1 Nano board is not an official Arduino, Johnson-Davies went to great lengths to give it the same size and pinout as existing Nano boards. It most resembles the newer Arduino Nano 33 series boards. All components are on the top side of the board, and the silk screen identifiers for pin names are on the bottom.

Initially, Johnson-Davies debated between the Nano 33 and Adafruit Feather form factors. However, the decision to follow the Nano came about because the 8-bit boards are popular for 5-volt applications, and the Feather form factor targets 3.3-volt.

Unlike many Arduino-derived boards, the RA4M1 Nano does not require a special board package in the Arduino IDE! From the IDE's perspective, the RA4M1 Nano looks just like an Arduino Uno R4 Minima. For example, you can use the same bootloader for the Uno R4 Minima on this smaller board! Despite this similarity, Johnson-Davies warns of a few minor differences.

One difference is that the Uno R4 Minima uses a voltage divider to monitor the 5 volt rail on an analog pin. The RA4M1 Nano has this divider but with more readily available E12-series resistor values. If you use this pin to check the voltage of the rail, you will need to adjust the conversion factor slightly. The analog inputs also have a minor difference. No A6 or A7 exists since the Uno R4 Minima does not support them. And A0 is located where A7 is on the Nano 33 boards. Also, the Uno R4 Minima sported a switching regulator that could accept up to 24 volts on VIN. The RA4M1 Nano uses a linear regulator and can only accept up to 12 volts.

Assembly is easy enough that individuals can solder these boards with a hot air tool. The Renesas R4AM1 has a 64-pin LQFP footprint, and Johnson-Davies used 0805-sized devices for the passive components. Since all components are on one side, you only need a single stencil to apply the solder paste.

Head over to the R4AM1 Nano post on Technoblogy for detailed information on the board. For example, Johnson-Davies explains how to flash the bootloader with DFU mode. You'll also find links to the GitHub Repo with the EAGLE design files. Alternatively, the blog post also has links to order PCBs directly from OSH Park or PCB Way.