[Leejohnston]

Thread 7 — Microcontrollers & Embedded Systems 
How Real Devices Think, Sense and Control the World 

Microcontrollers power almost everything around you — 
from washing machines and thermostats 
to drones, cars, game controllers, and industrial robots.

This thread teaches the fundamentals: 
what microcontrollers are, how they work, and how you can begin using them.

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1. What Is a Microcontroller?

A microcontroller (MCU) is a small, self-contained computer built onto a single chip.

It typically includes:
• a CPU (processor) 
• RAM 
• flash memory 
• input/output pins (GPIO) 
• timers/counters 
• ADC (analog-to-digital converter) 
• communication modules (UART, I2C, SPI) 

MCUs run compact programs that control real-world systems.

Famous examples: 
• Arduino (ATmega328P) 
• ESP32 
• ESP8266 
• STM32 
• Raspberry Pi Pico (RP2040) 

Unlike desktop computers, MCUs are built for one purpose — 
to repeatedly perform specific tasks with reliability.

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2. Microcontroller vs Microprocessor

Microcontroller (MCU): 
• all-in-one chip 
• designed for control tasks 
• low power 
• simple programs 
• interacts directly with hardware 

Microprocessor (CPU): 
• requires external RAM/ROM 
• used in PCs, phones 
• high speed 
• complex operating systems 

If a device reacts to sensors or controls motors, 
it likely uses a microcontroller.

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3. The Architecture of a Microcontroller

Typical MCU internal structure:

• CPU — executes instructions 
• Flash memory — stores your program 
• SRAM — working memory 
• EEPROM — long-term data storage 
• GPIO ports — control external components 
• Timers — generate precise delays 
• ADC — convert analog voltage to digital 
• DAC — convert digital to analog (some MCUs) 

This tiny chip can manage an entire device on its own.

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4. GPIO — Digital Inputs & Outputs

"General Purpose Input/Output" pins let the MCU communicate.

Digital output examples: 
• turn an LED on/off 
• control a motor driver 
• send digital signals to other chips 

Digital input examples: 
• read a button 
• read sensors 
• detect logic signals 

A GPIO pin is the microcontroller’s window to the world.

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5. Timers, PWM & Controlling Motors

MCUs contain timers that allow:

• accurate delays 
• event triggers 
• Pulse Width Modulation (PWM) 

PWM is used to: 
• dim LEDs 
• control servo motors 
• control DC motor speed 
• generate analog-like signals 

Example PWM idea: 
A 50% duty cycle = LED half brightness 
A 10% duty cycle = LED dim 
A 90% duty cycle = LED bright 

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6. Analog Inputs — ADC

Many sensors output analog voltages.

Examples:
• temperature sensors 
• light sensors (LDR) 
• potentiometers 
• gas sensors 
• microphones 

An ADC converts voltage into a number the MCU can use.

Example: 
10-bit ADC → value between 0 and 1023.

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7. Communication Protocols (UART, SPI, I2C)

UART: simple serial communication (text, debugging) 
SPI: fast, used for displays & flash memory 
I2C: two-wire bus used for sensors 

MCUs use these to talk to:
• gyroscopes 
• accelerometers 
• displays 
• other microcontrollers 

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8. Real Examples of Embedded Systems

• drones using sensors + motor controllers 
• thermostats reading temperature & switching relays 
• robots tracking input and moving motors 
• smart watches monitoring heart rate 
• automotive control units 
• home automation systems 

Embedded systems run modern life.

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9. Example Beginner Project (with Code)

Blink an LED — the “Hello World” of embedded systems

Arduino code:

Code:

void setup() {
  pinMode(13, OUTPUT);  // configure pin 13 as output
}

void loop() {
  digitalWrite(13, HIGH); // turn LED on
  delay(500);
  digitalWrite(13, LOW);  // turn LED off
  delay(500);
}

This simple program demonstrates:
• GPIO configuration 
• digital output 
• timing 
• infinite loops 

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10. Intermediate Example — Read a Sensor

Analog temperature sensor (LM35):

Code:

int sensorPin = A0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  int reading = analogRead(sensorPin); 
  float voltage = reading * (5.0 / 1023.0);
  float temperatureC = voltage * 100;

  Serial.println(temperatureC);
  delay(500);
}

Shows:
• ADC usage 
• voltage conversion 
• temperature calculation 
• UART output 

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11. What You Can Build With MCUs

• robots 
• RC cars 
• drones 
• weather stations 
• security systems 
• IoT devices 
• cat/dog feeders 
• automatic greenhouse controllers 
• full home automation systems 

The possibilities are endless.

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12. Recommended Next Steps

• Thread 8 — Power Electronics & Motor Drivers 
• Thread 9 — Digital Signal Processing Basics 
• Thread 10 — Build Your Own Microcontroller Project 

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End of Thread — Microcontrollers & Embedded Systems