The Microcontroller World — AVR, ARM Cortex-M, ESP32, RP2040

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Learn with your AI

Open this lesson in your favourite AI. It'll walk you through the why, explain the demo, and quiz you on the try-it list.

Open in Claude Open in ChatGPT

Why this matters

Picking the wrong MCU is the single most expensive mistake in IoT product design: it sets your power budget, your toolchain, your radio options, and your unit cost for the next five years. The market today splits into four practical camps — AVR / PIC (legacy 8-bit, Arduino Uno class), ARM Cortex-M (STM32, NRF52, SAMD — the mainstream professional choice), ESP32 family (Wi-Fi + BLE on-die, dominant in maker and Asian consumer IoT), and RP2040 (Raspberry Pi's dual-core M0+, increasingly the hobby default). The way to choose isn't 'which one is best' — it's 'which one fits the four constraints my product cares about: cost, power, radio, ecosystem.'

Demo

Side-by-side spec sheet for the four families.

Try it yourself

For each of the four families, pick one real shipped consumer or industrial product that uses it. (Hint: teardown.com and ifixit.com are gold mines.)
Pin down the four constraints (cost, power, radio, ecosystem) for a product idea of your own. Then map them to one of the families and write one sentence on why you'd reject each of the other three.
Open the datasheet for the ESP32-WROOM-32E and find the line that gives modem-sleep current draw. Compare it to the figure in the table above. Datasheets are the source of truth; comparison tables are sales material.

Prompt your AI

Use these three in order. Each builds on the one before.

1. Basics & terminology

In one paragraph, explain what a microcontroller is and how it differs from a general-purpose CPU like the one in a laptop.

2. Why it works (the mechanism)

Walk me through what happens when an ESP32 wakes from deep sleep, including which peripherals are still powered, where the program counter resumes, and how it re-establishes Wi-Fi.

3. Advanced — application & what's next

Given a battery-powered asset tracker that must run for 3 years on a single CR2032 coin cell and report GPS location once a day over LTE-M, which MCU family would you choose and what compromise would you make on the other three constraints?

References

Family ATmega328P STM32F4 ESP32-WROOM-32E RP2040 (Arduino Uno) (Cortex-M4) (Tensilica LX6) (Cortex-M0+ x2) ───────────────────────────────────────────────────────────────────────────────── Cores 1 1 2 2 Architecture 8-bit AVR 32-bit ARMv7E-M 32-bit Xtensa 32-bit ARMv6-M Clock 16 MHz 84-180 MHz 240 MHz 133 MHz Flash 32 KB up to 2 MB 4 MB (external) no on-chip (uses ext. QSPI) RAM 2 KB 128-256 KB 520 KB 264 KB FPU ✗ single-precision ✗ (LX6) ✗ Wi-Fi ✗ ✗ (add module) ✓ (built-in) ✗ (add module) Bluetooth ✗ ✗ (add module) ✓ BLE 4.2 ✗ ADC 10-bit 12-bit 12-bit (noisy) 12-bit USB ✗ (need FTDI) USB FS/HS ✗ (need bridge) ✓ FS device + host Cost (chip, 1k) ~$2 ~$5-15 ~$2-4 ~$1 Toolchain Arduino IDE, STM32CubeIDE, Arduino, ESP-IDF, Arduino, Pico SDK, avr-gcc arm-none-eabi-gcc PlatformIO CircuitPython Sleep current 0.1 µA 0.3-2 µA ~10 µA deep ~1 mA (no deep ~150 µA modem sleep on chip) Killer use case Teaching; Real industrial Wi-Fi/BLE-needed Hobby, USB devices, simple sensors / safety / RT consumer IoT PIO state machines DECISION MATRIX ─────────────── Need Wi-Fi or BLE on the chip itself? → ESP32, NRF52 (BLE), or add a module Need very low sleep current (years on battery)? → STM32L, NRF52, ATmega328P Need professional ecosystem (debugger, RTOS)? → STM32 (Cortex-M) Cheap and good enough? → RP2040 or ESP32 Safety-critical / regulated industry? → STM32 / NXP / TI (mature M-class)