An ATmega4809 "Breadboard Arduino"
David Johnson-Davies' minimal microcontroller is based on the same megaAVR 0-series processor as the Nano Every and Uno WiFi Rev2.
Unlike the classic Arduino Uno with its ATmega328P microcontoller, the newer Arduino Nano Every and Arduino Uno WiFi Rev2 are based on the ATmega4809 from Microchip's megaAVR 0-series.
Aside from more program memory and RAM than the ATmega328P, the ATmega4809 has some interesting features, including a faster 20 MHz clock, configurable logic, and an event system. It's also the only member of its family available in a breadboardable DIP package for easy prototyping. Naturally, Technoblogy’s David Johnson-Davies went to work turning the chip into a DIY next-gen “Arduino,” complete with a USB interface.
His design takes two forms, the slightly simpler of which mounts an FTDI USB-to-serial board on the the breadboard for communication. The other option uses an MCP2221A USB-to-serial converter on the board itself, which involves soldering a USB connector up to a four-pin header for data transfer. This version has a reset button as well, needed to set the chip up to program as it lacks the proper handshaking signal.
To get it functioning, Johnson-Davies also had to install a bootloader on the ATmega4809. The one provided by Arduino doesn’t work here, but he was instead able to implement a core for the megaAVR 0-series written by Hans Eirik Bull. Once done, the MCU/breadboard can be programmed like a normal Arduino in the IDE, or you can even get feedback over the serial monitor for troubleshooting. Perhaps you could install Johnson-Davies’ uLisp interpreter that we featured here, running on an ATtiny3216.