He also used a modular design where one block has the ESP32 and RTC, but for the additional blocks those components can remain unpopulated.

Adafruit has announced the availability of the ESP32-S2 WROOM Module with PCB Antenna equipped with 4 MB flash and available to purchase priced at just ...

In terms of hardware, the custom PCB is home to an ESP32 WROOM, a MAX98357A I2S audio amplifier, a FT231XS USB-to-serial chip, with enough passives and regulators to keep them all well fed and happy.