We present to our readers a book about digital electronics. “From simple to complex” examines code examples and connection diagrams for the most popular components: Arduino, Raspberry Pi, BBC Micro:bit, ESP and ESP32, and the “classic” type NE555 is not forgotten. Connection methods and examples of using various modules are also discussed: LCD screens, real-time clocks, motor control, etc. The book is designed for those starting their journey in mastering electronics, and for schoolchildren from 10-12 years old. Therefore, the theory is given in a minimal amount, and the main emphasis is on practical exercises. The book is distributed free of charge in electronic form, the latest version can be downloaded at To preserve the formatting of the text and code, it is recommended to select the PDF format for reading. Text version 1.4. Contents Part 1. Basics of Electronics - Parts and Tools - Electrical circuit - Measurements - Symbols on diagrams - Experiments with LED - Experiments with capacitors - NE555 microcircuit - Field-effect and bipolar transistors Part 2. Using Arduino - Basics of the C language - Data types in Arduino - Flashing the LED - Width - pulse modulation - Data output via Serial port - Button press detection - Input of analog values - Audio output - DS1820 temperature sensor - Connecting an OLED screen - Connecting a gyroscope, compass and accelerometer - Real time clock (RTC) - Connecting an ultrasonic range finder - Connecting a motor control module - Multiwii - making a quadcopter - Internet access: ESP Serial to WiFi Part 3. ESP32 - General introduction - I/O ports - Connect to WiFi - Connect the display - Get the time from the atomic clock - Display the number of friends in “Contact” - We display the number of subscribers, views and likes on Youtube - We launch our own Web server - We control the LED via the Web - We display images on the web server - Remote monitoring - We make a one-way messenger - Cloud services: we send data via Dropbox Part 4. Single board computer with Linux Raspberry Pi - General introduction - System setup - Basic Linux commands - Python language basics - GPIO: input/output ports - Using I2C - Connecting an OLED display - Connecting buttons - Going to the Web: make requests to the server - Launch your HTTP server - Remote control from a smartphone - Connect a webcam - Launch video surveillance - Time-lapse photography - Connect to the camera using OpenCV - Launch a video broadcast server - Send data via Dropbox - Face recognition using OpenCV Part 5. BBC Micro:bit - a computer for the little ones - Introduction - The first program for BBC Micro:bit - I/O capabilities - Controlling board tilts - using the accelerometer - Game “Snake” - Playing sound - Using the radio module - Using the serial port - Connecting external devices