Microcontroller (MCU)
IC (Compute)
A tiny computer on a chip: CPU, memory and I/O pins in one package. You program it to read sensors, drive outputs and run the logic of a product.
Schematic symbol
Integrated circuit (DIP)
How microcontroller (mcu) appears in a circuit diagram.
Types & variants
Key specs
Core / clock
MHzArchitecture and speed (e.g. 16MHz AVR, 240MHz ESP32).
Flash / RAM
KBProgram storage and working memory.
GPIO / peripherals
-Number of pins; ADC, PWM, UART/SPI/I2C, timers.
Operating voltage
VTypically 1.8-3.3V or 5V; watch pin logic levels.
Connectivity
-Built-in Wi-Fi/Bluetooth/USB/CAN on some parts.
Markings
Part number laser-etched on top; pin 1 dot/notch. Use the datasheet pinout - it varies per chip.
Standard values
ATmega328P, ATtiny85, STM32F103/F4, RP2040, ESP32, ESP8266.
How to choose
Match needs: pins, flash/RAM, ADC/PWM, comms (Wi-Fi?), voltage and power budget. Pick one with good toolchain/community (Arduino, STM32Cube, ESP-IDF). Start on a dev board, then bare chip.
Pinout & package
Power + GND, crystal/oscillator (some), reset, and GPIO multiplexed with peripherals. DIP (ATmega), QFP/QFN (STM32), modules (ESP32). Add decoupling caps on every VCC.
Example circuits
- Read a sensor over I2C and show on a display
- PWM motor/LED control
- Wi-Fi data logger (ESP32)
- Button + debounce + relay control
Common failures
Bricked by bad firmware (re-flash/bootloader), latch-up or fried pin from over-voltage/static, brown-out from a weak supply, missing decoupling causing resets.
How to test
Flash a blink program. Check 3.3/5V on VCC pins and a clean reset line. No serial/upload = check bootloader, crystal, and power.
Substitutes
Same family/footprint with >= flash/RAM/pins (e.g. ATmega168->328). Cross-family swaps mean re-writing firmware.