Definition
A microcontroller (MCU) is a single chip that packs a CPU core, a small amount of RAM and flash memory, and a set of I/O peripherals onto one inexpensive die. Unlike a full System-on-Chip running Linux, an MCU typically runs a single firmware image "bare metal" or under a tiny real-time OS. It is the workhorse of embedded electronics, and it sits at the heart of the open-source Bitcoin mining movement.
MCUs in open-source mining
The Bitaxe and its relatives are built around the Espressif ESP32-S3, a Wi-Fi-capable MCU that runs AxeOS, drives the single hashing ASIC, serves the web interface, and connects to a pool over Wi-Fi. NerdMiner and NerdNOS devices likewise run on ESP32-class microcontrollers. The MCU's low cost and simplicity are exactly what make a $100-class solo-mining device possible — there is no separate computer, just one chip doing everything.
MCU versus the big SoC
An Antminer's Zynq SoC is overkill for a single-chip miner; it exists to coordinate dozens of ASICs and run a full Linux stack. An MCU trades that horsepower for low cost and low power, which suits a small, transparent, hackable device far better. This is one reason open-source miners are so approachable: the entire firmware fits on one well-documented chip.
For the larger integrated processor used in industrial miners, contrast this with System-on-Chip (SoC).
In Simple Terms
A microcontroller (MCU) is a single chip that packs a CPU core, a small amount of RAM and flash memory, and a set of I/O…