Choosing an MCU

Picking a microcontroller is a trade-off between performance, peripherals, power, cost, robustness and ecosystem — not a single number. This page covers the common families, how to choose, and the traps to avoid.

Popular families

Family	Core / ISA	Sweet spot
AVR (ATmega/ATtiny), PIC, 8051	8-bit	Cheap, simple, robust, low performance — Arduino Uno is AVR
STM32 (ST)	Arm Cortex-M0/M3/M4/M7/M33	The lab default — huge range, rich peripherals, great tooling
ESP32 (Espressif)	Xtensa / RISC-V	Built-in Wi-Fi + BLE — IoT
Nordic nRF52/nRF53	Cortex-M	Bluetooth Low Energy / low power
RP2040 / RP2350 (Raspberry Pi)	Cortex-M0+ / M33 + RISC-V	Cheap, dual-core, hobby & education
TI MSP430	16-bit	Ultra-low-power sensing
NXP, Renesas, Microchip SAM	Cortex-M	Industrial / automotive breadth
GD32, WCH CH32V, SiFive	RISC-V	Low-cost, open ISA, growing ecosystem

Selection criteria

• Performance — see the gotchas below; judge the core + features, not just MHz.
• Peripherals — the right count and type: ADC resolution/channels, timers/PWM, UART/I²C/SPI/CAN/USB/Ethernet.
• Memory — enough flash + RAM, with headroom (an RTOS and stacks eat RAM).
• Power — active and sleep currents, low-power modes — critical for battery devices.
• Connectivity — is Wi-Fi/BLE/Thread/cellular integrated, or external?
• Cost — unit price at your volume, plus dev-board and tooling cost.
• Availability & lifecycle — current stock, longevity/EOL, and a second source. Supply shocks (2021–2022) stranded designs built around single-source parts.
• Operating temperature — match the grade to the environment (see below).
• Robustness & safety — brown-out detect, watchdog, ESD rating, ECC memory; safety certs (IEC 61508, ISO 26262) for critical systems.
• Ecosystem & compatibility — toolchain, HAL/RTOS support, debugger, community, and pin-compatible family members so you can scale up/down without a redesign.
• Security — TrustZone (Cortex-M33), secure boot, hardware crypto.

Operating temperature grades

Grade	Typical range	Use
Commercial	0 … +70 °C	Indoor consumer
Industrial	−40 … +85 °C	Most real-world / outdoor
Automotive (AEC-Q100)	−40 … +125 °C	Vehicles, harsh environments

Match the grade to the environment

A commercial-grade part in an outdoor or engine-bay device will drift or fail. For anything beyond a benign indoor setting, default to industrial (−40…+85 °C).

Gotchas — read before you commit

Don't pick on clock speed alone

MHz is only part of performance. Two chips at the same clock can differ several-fold:

• Architecture / IPC — a Cortex-M7 does far more per cycle than an M0+; DMIPS/MHz varies by core.
• FPU — without a hardware floating-point unit, every float is emulated in software (often 10×+ slower). An M4 @ 80 MHz with FPU can beat an M0 @ 100 MHz on math.
• DSP instructions — Cortex-M4/M7 SIMD/MAC accelerate filtering and control loops.
• Flash wait states / cache — at high clocks the flash can't keep up; an accelerator/cache (or running from RAM) is what delivers the rated speed.

FPU: know what you need

Most Cortex-M4/M7 have a single-precision FPU. If your code needs double precision and the FPU is single-only, those doubles still run in software. Match the FPU to your math.

RISC-V vs. Arm

	Arm Cortex-M	RISC-V
Ecosystem	Mature — tools, RTOS, libraries, support	Younger, growing fast
ISA	Licensed (vendors pay Arm)	Open, royalty-free, customizable
Risk	Very low, proven	Tooling/fragmentation still settling
Cost trend	—	Often cheaper silicon

• Choose Arm for proven tooling, broad RTOS/library support, and lowest project risk (the safe default today).
• Choose RISC-V for cost, openness, or custom silicon — and accept a less mature ecosystem.

Other things people forget

• Check the errata sheet — silicon bugs are real and can block a peripheral you rely on.
• Dev board + debugger availability — you want to prototype on day one (e.g. ST-Link/J-Link; see Programmers & Debuggers).
• Footprint/pin compatibility within a family lets you change memory/speed late without a board respin.

A quick decision flow

1. Connectivity? Need Wi-Fi/BLE → ESP32 / nRF. Otherwise a plain MCU.
2. Performance & math? Heavy float/DSP → Cortex-M4/M7 with FPU. Simple I/O → M0+/8-bit.
3. Environment? Outdoor/harsh → industrial/automotive grade.
4. Power? Battery → low-power family (MSP430, nRF, STM32L).
5. Cost & supply? Check unit price and live stock + a second source.
6. Ecosystem? Favor a family your team and tools already support.

See also: Firmware Approaches and the lab's Microcontrollers hardware guide.