Mastering The Arduino Uno R4Programming and Projects for the Minima and WiFi Based on the low cost 8 bit ATmega328P processor, the Arduino Uno R3 board is likely to score as the most popular Arduino family member, and this workhorse has been with us for many years. Eleven years later, the long overdue successor, the Arduino Uno R4, was released. It is built around a 48 MHz, 32 bit Arm Cortex M4 microcontroller and provides significantly expanded SRAM and Flash memory.