The IoT market is an emerging one. New hardware solutions appear almost daily, while others disappear quickly. At the moment of writing the first version of this book (2016-2019), some hardware solutions that seemed to be prominent for at least a couple of years existed. After a few years, while the 2nd edition of the publication is being prepared (2023–2025), most of the hardware solutions described previously are still present on the market, even strengthening their position and having modernized and improved versions (e.g. ESP32 as the successor of ESP8266). However, some other platforms increased their popularity, mainly because of their appearance in the VSCode programming environment with PlatformIO, and what is even more important, the possibility of writing programs in the Arduino model. In the following sections, a short review of these platforms is provided.

• AVR: Arduino – a development board using the Atmel microcontroller, undoubtedly the most popular development platform for enthusiasts and professionals. Arduino itself barely offers networking capabilities yet; there is a vast number of extension boards, including network interfaces (both wired and wireless);
• ESP: Espressif (Espressif Systems) – the great SoC solutions with wireless network interfaces built-in; the family of Espressif chips includes ESP8266 (WiFi) and ESP32 (WiFi, Bluetooth)
• nRF52: Nordic Semiconductor SoC that is based on ARM architecture and offers NFC, Bluetooth and ZigBee capabilities
• STM32: Another ARM-based family of SoCs; some of them have Bluetooth wireless module built-in
• ARM: Raspberry Pi (and its clones) – advanced boards, including Linux operating system with GUI interface, even able to replace desktop computers. There are also, however, low-powered, constrained devices with ARM cores, such as Cortex-M0+ (Raspberry Pi Pico: RP2040).

The following chapters are dedicated to the families of the devices, describing their main features:

• Arduino

• ESP8266 ESP8266 Jarek Paduch

• ESP32 [jpaduch] ESP32 Jarek Paduch

• nRF52 [ktokarz] nRF52

• STM32 [pczekalski] STM32

• Raspberry PI RPI Oleg Antemijczuk