Arduino, ESP32 and friends

The word Arduino gets used for three different things.

First, it is a company. Arduino designs and sells boards.

Second, it is an ecosystem. That means a whole family of tools and people that work together. It includes the Arduino IDE, the program you type your code into. It includes a core for each kind of chip, the behind-the-scenes code that makes simple commands work on that chip. It also has thousands of free libraries and a huge community of people sharing projects.

Third, it is the name of a single board, such as the Arduino Uno R4 Minima. That is the 5-volt board this course uses.

Here is the confusing part. The ecosystem reaches beyond the company's own boards. Espressif makes the ESP32 chips, and it publishes its own Arduino core. So you can program an ESP32 board in the Arduino IDE with the same commands. When someone says "it's an Arduino", they might mean "it runs Arduino code", not "Arduino built it". In this course, a bare "Arduino" means the ecosystem. A board always gets its full name.

Arduino names three things, and a sentence can mean any of them:

• The company, Arduino, which designs and sells boards.
• The ecosystem: the Arduino IDE (the program you write code in), the Arduino core for each family of chips (the code that makes digitalWrite() work on that chip), thousands of libraries, and the documentation and community around them. An ecosystem is the whole set of tools, code and people that work together.
• A board: one specific product, such as the Arduino Uno R4 Minima, this course's 5 V board.

The ecosystem is wider than the company's own boards. Espressif, the company behind the ESP32, publishes an Arduino core for its chips, so an ESP32-S3 board is programmed with the same IDE and the same function names. "It's an Arduino" may therefore mean "it runs Arduino code" rather than "Arduino made it". When a page in this course says Arduino, it means the ecosystem; when it means a board, it names the board in full.

"ESP32" can mean four different things, each one inside the next, like boxes inside boxes.

1. The family. Espressif calls it a series. Every chip whose name begins with ESP32 is in it: the original ESP32, the S2, S3, C3, C6, H2 and more. They are different chips, with different processors and different radios.
2. The chip. One member of the family, such as the ESP32-S3. It has two processor cores running at 240 MHz, Wi-Fi, and Bluetooth Low Energy. One chip that holds a processor, memory and a radio is called a system on chip, or SoC.
3. The module. A tiny board under a metal lid. It holds the chip, flash memory for the program, a crystal that keeps the clock steady, and an antenna. The ESP32-S3-WROOM-1 is one. Companies that build products solder a module onto their own board. That saves them designing the tricky radio part.
4. The development board, or dev kit. A module on a bigger board with the extras you need at a desk: a USB port, a part that turns USB's 5 volts into 3.3 volts, buttons, and rows of pins. The ESP32-S3-DevKitC-1 is this course's 3.3-volt board.

The family members really are different. The ESP32-S2 has Wi-Fi but no Bluetooth. The ESP32-H2 has no Wi-Fi at all. It has Bluetooth Low Energy and a radio for smart-home networks called Thread and Zigbee. The ESP32-C6 has all three. So "an ESP32 project" tells you very little until someone names the exact chip.

"ESP32" can name any of four nested things:

1. A family (Espressif says series): every chip whose name starts ESP32. The original ESP32, the S2, S3, C3, C6, H2 and others are different chips with different processors and radios.
2. A chip: one member of the family, such as the ESP32-S3, a dual-core 240 MHz processor with 2.4 GHz Wi-Fi and Bluetooth 5 (LE) (Espressif, ESP32-S3). A chip that holds a processor, memory and radio on one piece of silicon is called a system on chip, or SoC.
3. A module: a small board with the chip, its flash memory, a crystal (the clock's timing part) and an antenna, under one metal shield. The ESP32-S3-WROOM-1 module has a 40 MHz crystal and a PCB antenna (module datasheet v1.8). Product designers solder modules onto their own boards rather than lay out a radio themselves.
4. A development board (dev board, dev kit): a module on a board that adds what a person at a bench needs: USB, a regulator to make 3.3 V from USB's 5 V, buttons and pin headers. The ESP32-S3-DevKitC-1 is this course's 3.3 V board (Espressif user guide v1.1).

Family members differ in ways that matter. The ESP32-S2's datasheet lists a 2.4 GHz Wi-Fi radio and no Bluetooth (ESP32-S2 datasheet v1.9). The ESP32-H2 has Bluetooth 5 (LE) and an IEEE 802.15.4 radio for Thread and Zigbee, and pairs with "another Espressif Wi-Fi SoC" for Wi-Fi (Espressif, ESP32-H2). The ESP32-C6 has Wi-Fi 6, Bluetooth 5 (LE) and 802.15.4 (Espressif, ESP32-C6). So "an ESP32 project" says little until the exact chip is named.

Many sensor chips are smaller than a grain of rice. Their legs are far too small and close together to push into a breadboard. A breakout board fixes that. It is a little board with the chip soldered on. It "breaks out" each tiny connection to a normal pin you can plug in.

A good breakout also adds the small helper parts the chip needs. It might add a part that steadies its power, or one that lets it run from a different voltage.

People also use "breakout" loosely for almost any small add-on board. Either way, ask the same questions you would for a dev board. Which chip is on it? What voltage do its pins expect? Has the seller published a circuit drawing? Chapter 1 turns those questions into a checklist.

A breakout board is a small circuit board that carries one part, often a sensor, and brings its tiny pins out to a row of ordinary header pins spaced to fit a breadboard. A good breakout also adds the few supporting parts the chip needs, such as a capacitor next to its power pin, and sometimes a regulator or a level shifter so the part can run from a different supply voltage than it was designed for.

The word is sometimes used loosely for any small add-on board. What matters is the same question as for dev boards: which chip is on it, what voltage its pins expect, and whether the seller publishes a schematic. Chapter 1 §4 turns that into a checklist.

You will meet other boards on forums and in shops. Here is where each one fits.

• The Raspberry Pi Pico 2 is a cheap microcontroller board. Its chip is the RP2350. It has two processor cores running at 150 MHz, 520 KB of working memory and 4 MB of program memory. The Pico 2 W adds Wi-Fi and Bluetooth.
• STM32 is a huge family of microcontrollers from the company STMicroelectronics. Factories and cars use lots of them. ST's own dev boards are called Nucleo.
• nRF52 is a family from Nordic Semiconductor, built for Bluetooth Low Energy. Many fitness bands use one.
• Teensy boards are small, fast boards from a company called PJRC. You can program them from the Arduino IDE.
• The ordinary Raspberry Pi, such as the Raspberry Pi 5, is the odd one out. It is not a microcontroller board. It is a tiny full computer with a microprocessor, and it runs Linux, an operating system. It takes seconds to start, not milliseconds. Pick it when a project needs a screen, files, or several programs running at once.

You also don't have to write firmware in C++. MicroPython and CircuitPython put a small Python runner on the chip. You type Python and it runs straight away, with no separate build step. This course uses C++ with Arduino's tools instead. Most libraries, examples and jobs use it, and it shows you what the chip is really doing. Python on a chip is a good second skill to pick up later.

Several other families sit beside this course's two boards. Each is a fine choice; they are named here so you can place them when they come up.

• Raspberry Pi Pico 2: a microcontroller board built on the Raspberry Pi RP2350 chip, with two Arm Cortex-M33 cores or two Hazard3 RISC-V cores (you choose at start-up) at 150 MHz, 520 KB of SRAM and 4 MB of flash. The Pico 2 W adds Wi-Fi and Bluetooth 5.2 (Raspberry Pi).
• STM32: STMicroelectronics' large family of Arm Cortex-M microcontrollers, widely used in industry. ST's own Nucleo boards are its dev boards.
• nRF52: Nordic Semiconductor's family of Bluetooth LE microcontrollers, found in many wearables.
• Teensy: small, fast Arm-based boards from PJRC that can be programmed through the Arduino IDE.
• Raspberry Pi (the computer, such as a Raspberry Pi 5): not a microcontroller board at all. It is a small full computer with a microprocessor that runs Linux, an operating system. It boots in seconds rather than milliseconds and is the right tool when a project needs a screen, files, or many programs at once.

Firmware need not be C++. MicroPython and CircuitPython put a Python interpreter (a program that reads and runs Python as it goes) on the microcontroller, so you type Python and see results without a compile step. This course uses C++ with the Arduino core, because that is what the libraries, datasheet examples and most jobs use, and because it shows what the chip is really doing. The Python route is a good second skill.