In Part 2 we looked at how the Arduino families fit together and how to choose a board for a project. This article is the companion reference. For every current Arduino board, shield, and kit on my buying list, you will find an overview, a photo, a feature list, and a card that shows where to buy it. Wherever Arduino publishes an official pinout diagram, which is the labeled map of what each pin on the board does, it is included too. At the end there is a section on retired boards, which no longer have buy links but still turn up in old tutorials, secondhand listings, and search results.
You do not have to read this from top to bottom. Use the list below to jump to a family, or scan for the board that your project mentions. A few things to know first. Terms like flash, SRAM, and PWM are explained the first time they appear (the Uno R3 overview does it), and the rest of the series goes deeper. The buy cards use affiliate links, which means I may earn a small commission at no extra cost to you, and each card shows every store that carries the board. The specs come from the manufacturers' documentation, so check the product page for anything critical before you order.
Jump to a family:
- Uno Series
- Nano Series
- Mega Series
- Due Series
- Leonardo and Micro
- MKR Series
- GIGA Series
- Portenta Family
- Nicla Series
- Opta Series
- Pro Mini and Fio
- Shields and Expansion
- Modulino Nodes
- Robots and Connected Devices
- Starter and Project Kits
- Legacy and Discontinued Arduino Boards
Uno Series
The Uno is the board most people start with, and the family now includes both the original R3 and the newer R4 boards, plus the very different Uno Q.
Arduino Uno Mini Limited Edition Pinout Diagram
Pinout: Arduino
Arduino Uno R3 Pinout Diagram
Pinout: Arduino
Arduino Uno R4 Minima Pinout Diagram
Pinout: Arduino
Arduino Uno R4 WiFi Pinout Diagram
Pinout: Arduino
Arduino Uno Q Pinout Diagram
Pinout: Arduino
Arduino Uno Q 4 GB Pinout Diagram
Pinout: Arduino
Nano Series
Nano boards are the compact members of the Arduino line. They fit across a breadboard, and they come in everything from the classic 5V Nano to wireless boards with built-in sensors. Check the voltage on each one, because the family mixes 5V and 3.3V boards.
Arduino Nano Pinout Diagram
Pinout: Arduino
Arduino Nano V3 Pinout Diagram
Pinout: Arduino
Arduino Nano Every Pinout Diagram
Pinout: Arduino
Arduino Nano 33 IoT Pinout Diagram
Pinout: Arduino
Arduino Nano 33 BLE Pinout Diagram
Pinout: Arduino
Arduino Nano RP2040 Connect Pinout Diagram
Pinout: Arduino
Arduino Nano ESP32 Pinout Diagram
Pinout: Arduino
Arduino Nano ESP32 with Headers Pinout Diagram
Pinout: Arduino
Arduino Nano 33 BLE Sense Rev2 Pinout Diagram
Pinout: Arduino
Arduino Nano Matter Pinout Diagram
Pinout: Arduino
Arduino Nano R4 Pinout Diagram
Pinout: Arduino
Arduino Nano Connector Carrier Pinout Diagram
Pinout: Arduino
Mega Series
The Mega boards are the large, pin-rich end of the classic Arduino line. They are built for projects that need many inputs and outputs at once.
Arduino Mega 2560 Pinout Diagram
Pinout: Arduino
Arduino Mega ADK Pinout Diagram
Pinout: Arduino
Due Series
The Due sits alone in this group. It is the board to look at when an 8-bit chip is not enough, as long as you can live with 3.3V logic.
Arduino Due Pinout Diagram
Pinout: Arduino
Leonardo and Micro
These two boards share a chip with built-in USB, which lets them behave like a keyboard, mouse, or other USB device.
Arduino Leonardo Pinout Diagram
Pinout: Arduino
Arduino Micro Pinout Diagram
Pinout: Arduino
MKR Series
The MKR boards are compact, 3.3V boards with battery charging built in. Most of them add a particular kind of connectivity, such as WiFi, LoRa, or cellular.
Arduino MKR Zero Pinout Diagram
Pinout: Arduino
Arduino MKR WiFi 1010 Pinout Diagram
Pinout: Arduino
Arduino MKR WAN 1310 Pinout Diagram
Pinout: Arduino
Arduino MKR GSM 1400 Pinout Diagram
Pinout: Arduino
Arduino MKR NB 1500 Pinout Diagram
Pinout: Arduino
Arduino MKR ENV Shield Rev2 Pinout Diagram
Pinout: Arduino
Arduino MKR ETH Shield Pinout Diagram
Pinout: Arduino
Arduino MKR CAN Shield Pinout Diagram
Pinout: Arduino
Arduino MKR GPS Shield Pinout Diagram
Pinout: Arduino
Arduino MKR THERM Shield Pinout Diagram
Pinout: Arduino
Arduino MKR RGB Shield Pinout Diagram
Pinout: Arduino
Arduino MKR 485 Shield Pinout Diagram
Pinout: Arduino
Arduino MKR MEM Shield Pinout Diagram
Pinout: Arduino
Arduino MKR Relay Proto Shield Pinout Diagram
Pinout: Arduino
GIGA Series
The GIGA is the most powerful Arduino aimed at hobbyists, and it keeps the familiar Mega and Due layout.
Arduino GIGA R1 WiFi Pinout Diagram
Pinout: Arduino
Arduino GIGA Display Shield Pinout Diagram
Pinout: Arduino
Portenta Family
Portenta is Arduino Pro, the line aimed at industry and product design. These are modules and add-ons that plug into carrier boards, so they work differently from the boards above.
Arduino Portenta H7 Pinout Diagram
Pinout: Arduino
Arduino Portenta H7 Lite Pinout Diagram
Pinout: Arduino
Arduino Portenta H7 Lite Connected Pinout Diagram
Pinout: Arduino
Arduino Portenta X8 Pinout Diagram
Pinout: Arduino
Arduino Portenta C33 Pinout Diagram
Pinout: Arduino
Arduino Portenta Max Carrier Pinout Diagram
Pinout: Arduino
Arduino Portenta UWB Shield Pinout Diagram
Pinout: Arduino
Arduino Portenta Mid Carrier Pinout Diagram
Pinout: Arduino
Arduino Portenta Hat Carrier Pinout Diagram
Pinout: Arduino
Nicla Series
The Nicla boards are tiny, sensor-focused boards that are about the size of a postage stamp. They are aimed at product developers, wearables, and edge AI.
Arduino Nicla Vision Pinout Diagram
Pinout: Arduino
Arduino Nicla Voice Pinout Diagram
Pinout: Arduino
Arduino Nicla Sense Env Pinout Diagram
Pinout: Arduino
Arduino Nicla Sense ME Pinout Diagram
Pinout: Arduino
Opta Series
Opta is Arduino's line of micro PLCs, which are rugged controllers for machines and buildings. They mount on a DIN rail (the standard metal rail inside electrical cabinets) and many of their outputs switch mains-level loads, so treat them with care.
Arduino Opta Lite Pinout Diagram
Pinout: Arduino
Arduino Opta RS485 Pinout Diagram
Pinout: Arduino
Arduino Opta WiFi Pinout Diagram
Pinout: Arduino
Pro Mini and Fio
These are small, no-USB boards meant to be built into a finished project. You program them with a separate USB-to-serial adapter.
Shields and Expansion
A shield is a board that plugs on top of another board to add a feature. This section covers the Arduino shield on the buying list.
Modulino Nodes
Modulino nodes are small, single-purpose modules that snap together with Qwiic cables. Each one does a single job, such as sensing distance or lighting up LEDs, and you chain them together instead of wiring a breadboard.
Arduino Modulino Buttons Pinout Diagram
Pinout: Arduino
Arduino Modulino Distance Pinout Diagram
Pinout: Arduino
Arduino Modulino LED Matrix Pinout Diagram
Pinout: Arduino
Arduino Modulino Motors Pinout Diagram
Pinout: Arduino
Arduino Modulino Movement Pinout Diagram
Pinout: Arduino
Arduino Modulino Vibro Pinout Diagram
Pinout: Arduino
Arduino Modulino Hub Pinout Diagram
Pinout: Arduino
Arduino Modulino Extender Pinout Diagram
Pinout: Arduino
Arduino Modulino Buzzer Pinout Diagram
Pinout: Arduino
Arduino Modulino Pixels Pinout Diagram
Pinout: Arduino
Arduino Modulino Joystick Pinout Diagram
Pinout: Arduino
Robots and Connected Devices
These two are finished devices, not bare boards. One is a wheeled learning robot, and the other is a pocket-sized IoT gadget with its own screen and battery.
Arduino Nesso N1 Pinout Diagram
Pinout: Arduino
Starter and Project Kits
Kits bundle the parts for a particular goal, from learning sensors to building a household gadget. Some include a board and some do not, so read each description.
Legacy and Discontinued Arduino Boards
This section covers the boards, shields, and kits that Arduino no longer makes or that retailers no longer stock. There are no buy links, because the aim here is identification. If you have inherited a box of old parts, or you found an old Arduino at a garage sale, use the photos, the specs, the pinouts, and the archived documentation links to work out what you are holding. The entries run roughly oldest to newest, starting with the earliest boards and ending with the retired kits and accessories. Most sketches written for these boards still run on current boards with little or no change.
Arduino Serial
Photo: Arduino.
The Arduino Serial is one of the very first Arduino boards. It talks to a computer through an RS-232 serial port, the wide D-shaped connector (called a DB9) that was on the back of every PC before USB took over. If you find a board with that connector, a big black chip, and no USB socket, you may be holding one of these.
It was designed to be built by hand, with the simplest through-hole parts possible, so assembling one was a learning exercise in itself. Modern computers no longer have serial ports, so to program one today you would need a USB-to-serial adapter. It is mostly of historical interest, but if you do inherit one, it is a piece of Arduino history.
Key features and specs:
- Programs and communicates over RS-232 (DB9 connector)
- Through-hole parts, designed to be assembled by hand
- ATmega8-class AVR microcontroller on the early boards
- No USB port: needs a USB-to-serial adapter on modern computers
- Replaced by the USB-based Arduino boards
Arduino USB
The Arduino USB board replaced the serial connection with USB by adding an FTDI chip, the small converter that lets a computer talk to the microcontroller as if it were a serial device. It was sold as a kit that you assembled yourself, and the documentation walks through soldering the surface-mount FTDI chip, which is the hardest step.
It is part of the lineage that led to the NG, the Diecimila, and finally the Uno. If you come across a hand-soldered board with an FTDI chip and a USB-B port, this may be what you have. The software you would use today has long since moved on, but the circuit is the same idea that every later board refined.
Key features and specs:
- USB connection through an FTDI FT232 chip
- Sold as a do-it-yourself soldering kit
- AVR microcontroller (early versions used the ATmega8)
- Predecessor of the NG, Diecimila, and Duemilanove
- Retired, replaced by later USB boards
Arduino NG (Nuova Generazione)
Photo: DustyDingo, Public domain, via Wikimedia Commons.
NG stands for Nuova Generazione, Italian for "new generation," and the board lived up to the name by being easy to plug in: it connected over USB, like the boards after it. The first NG boards used an ATmega8 chip, and later "Rev C" boards moved to the more capable ATmega168.
The one thing it lacks compared with later boards is auto-reset. To upload a sketch to an NG, you had to press the reset button at just the right moment. Arduino's documentation even has a guide to upgrading an NG with a single small capacitor so it resets itself the way a Diecimila does. If an old tutorial mentions timing the reset button, this is the board it was written for.
Key features and specs:
- Microcontroller: ATmega8 (early) or ATmega168 (Rev C)
- USB connection through an FTDI chip
- 14 digital I/O pins, 6 analog inputs
- No auto-reset: reset button pressed by hand before uploading (can be modified)
- Succeeded by the Diecimila
Arduino NG Pin Mapping (ATmega8)
Pinout: Arduino.
Arduino Diecimila
Photo: ッ Zach Hoeken ッ, CC BY-SA 2.0, via Wikimedia Commons.
Diecimila is Italian for "ten thousand." The board was named to mark a milestone for the project, and it introduced one beloved improvement: auto-reset. When you clicked Upload in the software, the board reset itself, so you no longer had to time a button press.
It looks like a classic blue Arduino, with a USB-B socket, a power jack, and a long white chip socket holding an ATmega168. Compared with the Uno, it has half the program memory (16 KB instead of 32 KB), and a small jumper selects whether it runs from USB or an external supply. A lot of early Arduino tutorials were written for this board, so if a project asks for a "Diecimila," a modern Uno will run the same code.
Key features and specs:
- Microcontroller: ATmega168, 16 MHz
- 16 KB flash, 1 KB SRAM, 512 bytes EEPROM
- 14 digital I/O pins (6 PWM), 6 analog inputs
- USB connection, power jack, ICSP header, reset button
- Auto-reset on upload, 5V operating voltage
Arduino Diecimila Pin Mapping (ATmega168)
Pinout: Arduino.
Arduino Duemilanove
Photo: Minime72706, Public domain, via Wikimedia Commons.
Duemilanove is Italian for "2009," the year the board came out, and it was the Arduino that most people learned on just before the Uno arrived. It looks almost identical to the Diecimila, but it picks between USB power and an external supply by itself, with no jumper to move.
Early boards use an ATmega168, and later ones use an ATmega328, which doubles the memory to 32 KB of flash and 2 KB of SRAM. You can tell them apart by the text printed on the chip. Nearly every sketch written for a Duemilanove works on an Uno without changes, so old books and tutorials that mention it are still usable.
Key features and specs:
- Microcontroller: ATmega168 or ATmega328, 16 MHz
- 16 KB or 32 KB flash, 1 KB or 2 KB SRAM
- 14 digital I/O pins (6 PWM), 6 analog inputs
- Automatic power source selection (USB or external)
- USB connection, power jack, ICSP header, reset button
Arduino Duemilanove Pin Mapping (ATmega168)
Pinout: Arduino.
Arduino Mega (original)
Photo: Arduino.
The first Arduino Mega was the board for projects that needed lots of pins. It used the ATmega1280 chip and gave you 54 digital pins and 16 analog inputs, which was a huge jump from the 14 and 6 on the other boards of the time. Like the current Mega, it also offered four hardware serial ports.
It was replaced by the Mega 2560, which doubled the program memory. The two boards look nearly the same, and sketches for one will normally run on the other, so if you have an older shield or project that says it needs a Mega, the 2560 is the modern equivalent.
Key features and specs:
- Microcontroller: ATmega1280, 16 MHz
- 128 KB flash, 8 KB SRAM, 4 KB EEPROM
- 54 digital I/O pins (14 PWM), 16 analog inputs
- Four hardware serial ports (UARTs)
- 5V logic, replaced by the Mega 2560
Arduino Mini
Photo: Arduino.
The Arduino Mini is a tiny board, only about 30 by 18 millimeters, made for breadboards and projects where space matters. It has no USB port, so you program it through a USB-to-serial adapter plugged into its header pins, which is the same approach the Pro Mini still uses today.
It was originally built on the ATmega168 and later on the ATmega328, and it gives you 14 digital pins and 8 analog inputs. If you are sorting through a box of parts and find a very small blue board with a row of through-holes along each side, it is probably a Mini. The Pro Mini and Nano are its modern successors.
Key features and specs:
- Microcontroller: ATmega328 (originally ATmega168), 16 MHz
- 32 KB flash, 2 KB SRAM, 1 KB EEPROM
- 14 digital I/O pins, 8 analog inputs
- Size: about 30 x 18 mm, no USB port
- Programmed through a USB-to-serial adapter, 7 to 9 V input
Arduino Mini Pinout Diagram
Pinout: Arduino.
Arduino Pro
Photo: Arduino.
The Arduino Pro was a full-size board for people who wanted to leave a project installed for a long time. It strips out the USB chip and the power jack and leaves holes for you to add the connectors you actually need, which keeps it cheaper and lets it fit into a finished product.
It came in two versions: 3.3V running at 8 MHz, and 5V running at 16 MHz, both with an ATmega328. To program one, you connect an FTDI cable or a USB-to-serial board to its six-pin header. If you are looking at a skinny blue board with no USB port and a six-pin header, it could be a Pro, or its smaller sibling, the Pro Mini.
Key features and specs:
- Microcontroller: ATmega328
- Two versions: 3.3V at 8 MHz or 5V at 16 MHz
- 32 KB flash (2 KB used by bootloader), 2 KB SRAM, 1 KB EEPROM
- 14 digital I/O pins (6 PWM), 6 analog inputs
- No USB port: six-pin header for an FTDI cable or adapter
Arduino Pro Pin Mapping (ATmega328P)
Pinout: Arduino.
Arduino BT
Photo: David Mellis, CC BY 2.0, via Wikimedia Commons.
The Arduino BT put a Bluetooth radio on an Arduino board, so a sketch could talk to a phone or computer without a cable. It carries a Bluegiga WT11 Bluetooth module, and it could even be programmed wirelessly. It uses Bluetooth for serial communication only, so it does not work with Bluetooth headsets or other audio devices.
It was originally based on the ATmega168, and later boards carry the ATmega328P. A green PCB with a large silver module on one end is the giveaway. Modern boards with Bluetooth Low Energy, such as the Nano 33 BLE, have taken its place.
Key features and specs:
- Microcontroller: ATmega328P (originally ATmega168), 16 MHz
- Bluegiga WT11 Bluetooth module for wireless serial communication
- 14 digital I/O pins, 6 analog inputs
- 32 KB flash, 2 KB SRAM, 1 KB EEPROM
- Input voltage 2.5 to 12 V, 5V operating voltage
Arduino BT Pin Mapping (ATmega328P)
Pinout: Arduino.
LilyPad Arduino
Photo: Arduino.
The LilyPad was designed by Leah Buechley and SparkFun Electronics for e-textiles, which means projects where circuits are sewn into clothing and fabric. The board is a flat round disc with large petal-shaped pads around the edge, so you can stitch it down with conductive thread instead of soldering. If you find a purple, round board in a drawer, it is very likely a LilyPad.
There were several versions. The Main Board has an ATmega168 or ATmega328 and 14 pins. The Simple has 9 pins plus a battery connector with built-in charging for lithium polymer batteries. The SimpleSnap has a battery built in and uses conductive snaps so you can remove it to wash your project. The LilyPad USB is built on an ATmega32U4 and connects with a micro USB cable. All run at low voltage and 8 MHz, so they sip power.
Key features and specs:
- Designed by Leah Buechley and SparkFun Electronics
- Main Board: ATmega168V or ATmega328V, 14 digital pins, 6 analog inputs
- Simple: ATmega328P, 9 pins, LiPo connector and charger
- USB: ATmega32U4, 9 pins, micro USB, 3.3V
- 8 MHz clock, 2.7 to 5.5 V operation (3.3V on the USB version)
- Large sew-through pads for conductive thread
Arduino Ethernet
Photo: Arduino.
The Arduino Ethernet is an Uno-style board with a wired network jack built right onto it, so there is no shield to stack on top. It is based on the ATmega328P with a WIZnet W5100 Ethernet controller, and an RJ45 connector sits on the end. A version with PoE (Power over Ethernet) could even be powered by the network cable itself through an add-on module.
Four of its pins (10 through 13) are reserved for talking to the Ethernet chip, so they are not available for your own use. There is also no USB port, so you program it through a header with an FTDI cable or adapter. It was a good fit for permanent, wired network projects such as door sensors and web-controlled relays.
Key features and specs:
- Microcontroller: ATmega328P, 16 MHz, WIZnet W5100 Ethernet controller
- 32 KB flash (0.5 KB used by bootloader), 2 KB SRAM, 1 KB EEPROM
- RJ45 Ethernet connector, microSD card slot
- Pins 10 to 13 reserved for the Ethernet chip
- Optional Power over Ethernet (36 to 57 V), 5V operating voltage
- No USB port: programmed with an FTDI cable or adapter
Arduino Leonardo ETH
Photo: Arduino.
The Leonardo ETH is a Leonardo with an Ethernet port added. It combines the ATmega32U4 chip, which handles USB on its own, with a newer W5500 Ethernet controller, so one board can act as a USB keyboard or mouse and also talk over a wired network. That is useful for connected control panels and gateways.
It has 20 digital pins (7 with PWM, and 12 that can read analog signals), a micro USB port, an RJ45 jack, and a microSD card slot. Pin 4 is used for the SD card and pin 10 for the Ethernet chip. A PoE (Power over Ethernet) version existed too. It has been retired, and current projects usually pair a newer board with an Ethernet shield or use WiFi.
Key features and specs:
- Microcontroller: ATmega32U4, 16 MHz, W5500 Ethernet controller
- 32 KB flash (4 KB used by bootloader), 2.5 KB SRAM, 1 KB EEPROM
- 20 digital I/O pins (7 PWM, 12 analog), 5V logic
- RJ45 Ethernet, micro USB, microSD card slot
- Pins 4 (SD) and 10 (Ethernet) reserved
- Optional PoE version
Arduino Leonardo ETH Pin Mapping (ATmega32U4)
Pinout: Arduino.
Arduino Yún and Yún Mini
Photo: Arduino.
The Yún (pronounced "yoon," Italian for "cloud") was Arduino's first board with two processors. One is the familiar ATmega32U4 microcontroller. The other is an Atheros AR9331 running a version of Linux called Linino OS (based on OpenWrt), the same kind of chip found in small WiFi routers. A software layer called Bridge lets your sketch hand work off to the Linux side.
The result was a board with built-in WiFi, Ethernet, a USB-A port, and a microSD slot that could fetch web pages, run scripts, and serve a web page, all while keeping Arduino's real-time pins. The Yún Mini is a smaller version that fits a breadboard. Both are retired, and today the Uno Q and Portenta X8 do the same job in a much more capable way.
Key features and specs:
- ATmega32U4 microcontroller (16 MHz, 32 KB flash, 2.5 KB SRAM) plus Atheros AR9331 (MIPS, 400 MHz)
- Linino OS (OpenWrt-based Linux), 16 MB flash, 64 MB DDR2 RAM
- WiFi 802.11 b/g/n 2.4 GHz and 10/100 Ethernet
- USB-A host port and microSD slot (Yún)
- 20 digital I/O pins (7 PWM, 12 analog), 5V logic
- Yún Mini: compact breadboard version
Arduino Yún Rev2 Pinout Diagram
Pinout: Arduino.
Arduino Uno WiFi
The original Uno WiFi is a regular Uno with a WiFi radio added. It uses the same ATmega328 chip as the Uno R3, paired with an ESP8266 WiFi module, so your sketch can join a network without a shield. The ESP8266 is a very popular low-cost WiFi chip in its own right.
It keeps the Uno shape and 5V logic, so existing shields fit. It was replaced by the Uno WiFi Rev2, and later by the Uno R4 WiFi. If you see an Uno with a small metal-shielded module near the USB connector, check the printing on the board to tell which generation you have.
Key features and specs:
- Microcontroller: ATmega328, 16 MHz, ESP8266 WiFi module
- 32 KB flash, 2 KB SRAM, 1 KB EEPROM
- 14 digital I/O pins (6 PWM), 6 analog inputs, 5V logic
- Uno layout: existing shields fit
- USB connection, power jack, ICSP header
Arduino Uno WiFi Pin Mapping (ATmega328P)
Pinout: Arduino.
Arduino Uno WiFi Rev2
Photo: Arduino.
The Uno WiFi Rev2 kept the Uno shape but rebuilt the inside. It uses an ATmega4809 processor, which has more memory than the original Uno chip, paired with a u-blox NINA-W13 module for WiFi and Bluetooth, a six-axis motion sensor, and a crypto chip for secure connections.
That made it a convenient board for connected projects that also needed to sense movement. It has been retired, and the Uno R4 WiFi is the modern replacement, with an LED matrix on top. Note that the Rev2 uses a different chip from the Uno R3, so a few libraries that talk directly to the old ATmega328 hardware may not work on it.
Key features and specs:
- Microcontroller: ATmega4809, 20 MHz, u-blox NINA-W13 (WiFi and Bluetooth)
- 6-axis motion sensor and ECC608 crypto chip
- Uno layout and 5V logic
- USB connection, power jack
- Retired, replaced by the Uno R4 WiFi
Arduino Uno WiFi Rev2 Pinout Diagram
Pinout: Arduino.
Arduino Zero
Photo: Arduino.
The Arduino Zero was the first board on the familiar Uno layout to use a 32-bit ARM processor. It is built around the ATSAMD21G18, a Cortex-M0+ running at 48 MHz, which gives it far more memory than the AVR boards, and it has a true analog output (a DAC) on one pin.
Its best feature is a built-in debugger. Most Arduinos have no way to pause a program and look inside, but the Zero has one on board, which is a big help when hunting a bug. It runs at 3.3V, so be careful with 5V parts. The MKR and Nano 33 families later built on the same chip.
Key features and specs:
- Microcontroller: ATSAMD21G18, 32-bit ARM Cortex-M0+, 48 MHz
- 256 KB flash, 32 KB SRAM
- 14 digital I/O pins (12 PWM), 6 analog inputs, 1 DAC output
- On-board debugger (Atmel EDBG), USB connection
- Uno layout, 3.3V logic
Arduino Zero Pinout Diagram
Pinout: Arduino.
Arduino M0 and M0 Pro
Photo: Arduino.
The M0 and M0 Pro are 32-bit versions of the Uno layout. Both use an ATSAMD21G18 Cortex-M0+ processor at 48 MHz, with 256 KB of flash and 32 KB of SRAM, which is a big step up from the 8-bit Uno. They run at 3.3V and add features like 12 PWM pins and a DAC.
The difference is that the M0 Pro includes a built-in step-by-step debugger, which lets you pause your program and inspect it as it runs. They are retired now, and the Zero and later MKR and Nano 33 boards cover the same ground. They came with the product codes A000103 (M0) and A000111 (M0 Pro).
Key features and specs:
- Microcontroller: ATSAMD21G18, ARM Cortex-M0+, 48 MHz
- 256 KB flash, 32 KB SRAM
- 20 digital I/O pins (12 PWM), 6 analog inputs plus 1 DAC output
- 3.3V logic, 5 to 15 V input voltage
- M0 Pro adds a built-in step-by-step debugger
- Product codes: A000103 (M0), A000111 (M0 Pro)
Arduino 101 (Genuino 101)
Photo: Arduino.
The Arduino 101 was built with Intel around the Curie module, a tiny chip that packs a processor, Bluetooth Low Energy, and a six-axis accelerometer and gyroscope into one package. It kept the Uno shape and pin layout, so existing shields fit, and it could recognize simple gestures, such as taps and steps, using the motion sensor.
The board runs at 3.3V with a 32 MHz processor, which was slow by modern standards, but the built-in Bluetooth and motion sensing made it a handy teaching board for wearables and connected projects. Intel retired the Curie, and Arduino retired the board with it. The Nano 33 BLE and Nano 33 IoT are the modern boards with similar features.
Key features and specs:
- Microcontroller: Intel Curie, 32 MHz, 3.3V logic
- Bluetooth Low Energy and a 6-axis accelerometer/gyro built in
- 196 KB flash, 24 KB SRAM
- 14 digital I/O pins (4 PWM), 6 analog inputs
- Uno layout: existing shields fit
- Retired when Intel discontinued the Curie module
Arduino Esplora
Photo: Arduino.
The Esplora looks like a game controller, and that is the point. It is based on the Leonardo, but instead of a row of pins it has a joystick, four buttons, a slider, a light sensor, a temperature sensor, a microphone, a 3-axis accelerometer, a buzzer, and an RGB LED all built in. You can plug in and start experimenting without touching a breadboard.
It was designed for people who want to start with Arduino without having to learn electronics first. Because it is built on the Leonardo's ATmega32U4 chip, it can also act as a USB keyboard or mouse. There is a socket on the side for an optional TFT screen. If you find a rounded blue board with a joystick, this is the one.
Key features and specs:
- Microcontroller: ATmega32U4, 16 MHz, 5V
- 32 KB flash (4 KB used by bootloader), 2.5 KB SRAM, 1 KB EEPROM
- On-board joystick, four buttons, and a slider
- Light, temperature, and sound sensors plus a 3-axis accelerometer
- Buzzer and RGB LED, connectors for extra inputs and outputs
- Socket for an optional TFT screen, can act as a USB keyboard or mouse
Arduino Esplora Pin Mapping (ATmega32U4)
Pinout: Arduino.
Arduino Robot
Photo: Arduino.
The Arduino Robot is a round wheeled robot made of two boards stacked together: a Control board on top and a Motor board underneath. Each has its own ATmega32U4 microcontroller. The Control board has a screen, buttons, and a compass, and the Motor board drives the wheels and reads sensors that let the robot follow a line on the floor.
It was Arduino's first official robot and was aimed at teaching, with a library for controlling it and a getting-started guide. It has been retired, but it is a good one to recognize: a yellow-and-white disc about the size of a dinner plate. Today, the Alvik and Braccio do the same job.
Key features and specs:
- Two stacked boards, each with an ATmega32U4 microcontroller
- Control board: screen, buttons, compass, and expansion connectors
- Motor board: two drive motors and sensors for following lines
- Programmed with the Arduino IDE and the Robot library
- Retired, replaced by newer educational robots
Arduino Gemma
Photo: Arduino.
The Gemma is a tiny round wearable board, about 28 millimeters across, built around an ATtiny85. It was made by Adafruit for sewing into clothing and costumes, and it has a connector for a small lithium battery and a micro USB port for programming.
It only has three pins, two of which can do PWM and one that can read an analog signal, and 8 KB of program space, so it works best for simple jobs like blinking or fading LEDs and reading one sensor. It is not a full-featured Arduino, but it is cheap and small. The Gemma was retired, and wearable projects today use boards such as the Nano family.
Key features and specs:
- Microcontroller: ATtiny85, 8 MHz, 3.3V
- 8 KB flash (2.75 KB used by bootloader), 512 bytes SRAM, 512 bytes EEPROM
- 3 digital I/O pins (2 PWM, 1 analog input)
- Micro USB port and a JST connector for a 3.7V battery
- Size: round, about 27.9 mm in diameter
- Made by Adafruit
Arduino Primo
Photo: Arduino.
The Primo was the first board Arduino developed with Nordic Semiconductor. It brings together a Nordic nRF52 processor for Bluetooth Low Energy, an ESP8266 for WiFi, NFC (near-field communication, the tap-to-pair technology in phones), and an infrared transmitter and receiver, plus several sensors and a battery charger. In total, there are three microcontrollers on the board.
The aim was to put every common wireless technology on one board for IoT experiments. It was retired and replaced by the Nano 33 and MKR boards, which are smaller and cheaper. A round version called the Primo Core was also made, with just the Nordic processor and no WiFi chip.
Key features and specs:
- Main processor: Nordic nRF52 with Bluetooth Low Energy
- Espressif ESP8266 for WiFi (80 MHz, 4 MB flash)
- NFC, infrared transmit and receive, and onboard sensors
- Battery charger, 3.3V operating voltage
- Three microcontrollers on one board
- Primo Core: a round version without the WiFi chip
Arduino Tian
Photo: Arduino.
The Tian is a two-processor board. A 32-bit SAMD21 microcontroller handles the real-time pins, and a Qualcomm Atheros AR9342 MIPS processor running at 560 MHz runs Linux (Linino OS, based on OpenWrt). It is a larger sibling of the Yún with much more power: dual-band WiFi, gigabit Ethernet, a USB host port, 64 MB of RAM, and 4 GB of built-in flash storage.
It was aimed at IoT gateways and projects that need a small Linux computer next to hard real-time control. It has been retired, and the Portenta X8 and Uno Q fill that role today.
Key features and specs:
- SAMD21G18 microcontroller (ARM Cortex-M0+, 48 MHz, 256 KB flash, 32 KB SRAM)
- Qualcomm Atheros AR9342 processor (MIPS, 560 MHz), 64 MB DDR2 RAM
- 16 MB flash plus 4 GB eMMC storage
- Dual-band WiFi 802.11 b/g/n (2.4 and 5 GHz), 10/100/1000 Ethernet
- USB 2.0 host port, Linino OS
- 3.3V logic
Arduino Tre
Photo: Arduino.
The Tre was the first Arduino made in the United States, and it was developed with BeagleBoard.org. It pairs an ATmega32U4 microcontroller with a 1 GHz Texas Instruments Sitara AM3359 processor, with 512 MB of RAM, running Linux. Texas Instruments described it as up to 100 times more powerful than the Leonardo or Uno.
It has HDMI video, stereo audio, 10/100 Ethernet, and four USB host ports, so it behaves like a small desktop computer with Arduino pins on the side. It was always a rare, high-end board and has been discontinued. The Portenta X8 and Uno Q are its modern descendants.
Key features and specs:
- ATmega32U4 microcontroller (16 MHz, 32 KB flash, 2.5 KB SRAM)
- Texas Instruments Sitara AM3359 processor, 1 GHz, 512 MB DDR3L RAM
- HDMI video and stereo audio input and output
- Ethernet 10/100, four USB 2.0 host ports, one USB 2.0 device port
- Runs Linux, made in the USA with BeagleBoard.org
Arduino Industrial 101
Photo: Arduino.
The Industrial 101 is a small Yún-style module designed to be built into other products. Like the Yún, it pairs an ATmega32U4 microcontroller with an Atheros AR9331 processor running Linino OS, and it has WiFi, an Ethernet connection, and a USB host port, but it is smaller and meant to be mounted on a baseboard.
It was aimed at manufacturers who wanted Arduino-compatible connectivity in a compact form. Only a few pins (3 GPIOs and 4 analog inputs) come out of the main module, and it was retired along with the Yún family.
Key features and specs:
- ATmega32U4 microcontroller (16 MHz, 2.5 KB SRAM) plus Atheros AR9331 (MIPS, 400 MHz)
- Runs LininoOS (OpenWrt-based Linux), 16 MB flash, 64 MB DDR2 RAM
- WiFi 802.11 b/g/n 2.4 GHz and 10/100 Ethernet
- USB 2.0 host port
- Small form factor for product integration
- Retired along with the Yún family
Arduino Industrial 101 Pinout Diagram
Pinout: Arduino.
Arduino MKR1000
Photo: MakeMagazinDE, CC BY-SA 4.0, via Wikimedia Commons.
The MKR1000 was the first board in the MKR family, the compact, battery-friendly line that Arduino built for IoT projects. It has a SAMD21 processor, a WiFi chip (the Atmel ATWINC1500), and a crypto chip for secure connections, in a board about the size of a few postage stamps.
It has a connector for a lithium polymer battery with a charging circuit built in, and it runs at 3.3V. Its pin layout set the pattern for every MKR board after it, which is why so many MKR shields still fit. It was replaced by the MKR WiFi 1010.
Key features and specs:
- Microcontroller: ATSAMD21G18, ARM Cortex-M0+, 48 MHz
- Atmel ATWINC1500 WiFi module and ECC508 crypto chip
- 256 KB flash, 32 KB SRAM, 3.3V logic
- Li-Po battery connector with built-in charger
- First board in the MKR family, replaced by the MKR WiFi 1010
Arduino MKR1000 Pinout Diagram
Pinout: Arduino.
Arduino MKR FOX 1200
The MKR FOX 1200 was built for Sigfox, a network designed to send very small messages over very long distances while using almost no power. It paired the SAMD21 processor with a Sigfox radio module, so a battery-powered sensor could report a reading from far away.
Sigfox's network has shrunk considerably in recent years, so the board has little practical use today, and it has been retired. LoRa and cellular boards, such as the MKR WAN 1310 and MKR NB 1500, are the usual alternatives.
Key features and specs:
- Microcontroller: ATSAMD21G18, ARM Cortex-M0+, 48 MHz
- Sigfox radio module for long-range, low-power messaging
- Li-Po battery connector with charger
- 3.3V logic, MKR form factor
- Retired, Sigfox network coverage has shrunk
Arduino MKR FOX 1200 Pinout Diagram
Pinout: Arduino.
Arduino MKR WAN 1300
The MKR WAN 1300 added LoRa, a long-range, low-power radio technology, to the MKR format. It used a Murata LoRa module and the SAMD21 processor, and it could talk to LoRaWAN networks to send small readings over several kilometers.
It was replaced by the MKR WAN 1310, which fixed a power-consumption issue so the board could sleep for long stretches on a small battery. If you have an old 1300, it still works, but the 1310 is the better choice for new projects.
Key features and specs:
- Microcontroller: ATSAMD21G18, ARM Cortex-M0+, 48 MHz
- Murata LoRa module for LoRaWAN networks
- Li-Po battery connector with charger
- 3.3V logic, MKR form factor
- Replaced by the MKR WAN 1310
Arduino MKR WAN 1300 Pinout Diagram
Pinout: Arduino.
Arduino MKR Vidor 4000
The MKR Vidor 4000 is one of the most unusual boards Arduino ever made. Next to its SAMD21 processor it carries an FPGA (an Intel Cyclone 10), a chip whose internal wiring you can reconfigure to build your own custom hardware. It also has a WiFi and Bluetooth module, a mini HDMI port for video output, and a camera connector.
It let makers design hardware such as video processors and extra serial ports and then use them from an Arduino sketch. FPGAs are hard to learn, so it never became a mainstream board, and it has been retired. It remains a fun find for anyone curious about programmable logic.
Key features and specs:
- Microcontroller: ATSAMD21G18, ARM Cortex-M0+, 48 MHz
- Intel Cyclone 10 FPGA for custom hardware
- u-blox NINA-W102 module: WiFi and Bluetooth
- Mini HDMI video output and a camera connector
- Li-Po battery connector, 3.3V logic
Arduino MKR Vidor 4000 Pinout Diagram
Pinout: Arduino.
Arduino MKR IoT Carrier
The first MKR IoT Carrier was a board that a MKR board plugs into, adding a small round display, touch buttons, relays, LEDs, and a set of sensors. It let students build a connected device without any wiring at all, and it was the heart of Arduino's educational IoT kits.
It has been replaced by the Rev2 carrier, which is the one that comes in the Explore IoT Kit. If you have an old kit with a round black board, this is probably the original.
Key features and specs:
- Carrier for MKR boards, no wiring needed
- Built-in display, touch buttons, relays, and LEDs
- Onboard sensors for environment and motion
- Used in Arduino's educational IoT kits
- Replaced by the MKR IoT Carrier Rev2
Arduino MKR IoT Carrier Pinout Diagram
Pinout: Arduino.
Arduino MKR IMU Shield
Photo: Arduino.
The MKR IMU Shield adds a motion sensor to a MKR board. It is built around the Bosch BNO055, a 9-axis sensor that combines an accelerometer, a gyroscope, and a magnetometer, and that works out its own orientation. That makes it good for projects like a tilt-aware gadget or a small robot that needs to know which way it is facing.
It plugs onto the top of a MKR board with no soldering. It is no longer sold, but later Nano boards and the Modulino Movement node cover the same ground.
Key features and specs:
- Bosch BNO055 9-axis orientation sensor
- Accelerometer, gyroscope, and magnetometer in one chip
- Plugs onto MKR boards, no soldering
- No longer sold, see the Modulino Movement node
Arduino MKR IMU Shield Pinout Diagram
Pinout: Arduino.
Arduino MKR Proto Shields
Photo: Arduino.
The MKR Proto Shield, the MKR Proto Large Shield, and the MKR SD Proto Shield were blank prototyping boards for the MKR family. Each had an open grid of holes where you could solder your own parts, and the SD version added a microSD card slot so you could store data.
They are no longer available, but a few remain in drawers. If you have one, it can still be used to build a permanent version of a project that you tested on a breadboard.
Key features and specs:
- Blank prototyping area with through-holes for your own parts
- Three versions: Proto, Proto Large, and SD Proto
- SD Proto adds a microSD card slot
- Plugs onto MKR boards
- No longer available
Arduino MKR SD Proto Shield Pinout Diagram
Pinout: Arduino.
Arduino Portenta Breakout
Photo: Arduino.
The Portenta Breakout makes every signal on a Portenta board's high-density connectors available as an individual pin. Those connectors are tiny and hard to wire by hand, so a breakout is a convenient way to probe signals and connect external hardware while you are developing.
It has been retired, and the Portenta Mid Carrier is the modern way to do the same job, with ready-made connectors added.
Key features and specs:
- Breaks out all Portenta high-density connector signals
- For prototyping and testing external hardware
- Compatible with the Portenta family
- Retired, see the Portenta Mid Carrier
Arduino Portenta Breakout Pinout Diagram
Pinout: Arduino.
Arduino Tiny Machine Learning Kit
Photo: Arduino.
The Tiny Machine Learning Kit paired a Nano 33 BLE Sense with a small camera module and a shield, and it was built for learning TinyML, which means running small machine-learning models on the board itself. Projects included recognizing words and gestures and identifying objects with the camera.
It is no longer being stocked by the retailers I checked. The Nano 33 BLE Sense Rev2 covers the same ground on its own, and the Nicla Vision is a more capable camera board.
Key features and specs:
- Nano 33 BLE Sense board with sensors
- OV7675 camera module and a TinyML shield
- Built for TensorFlow Lite for Microcontrollers projects
- No longer being stocked
Arduino Ethernet Shield (original)
Photo: Arduino.
The original Ethernet Shield plugged on top of an Uno or Mega and added a wired network port. It used the WIZnet W5100 chip, which supports a few simultaneous connections, and it had a microSD card slot as well. With it, your board could serve a web page or fetch data from the internet.
It uses pins 10 through 13 to talk to the Ethernet chip and pin 4 for the SD card. The newer Ethernet Shield 2 uses a W5500 chip. If your Arduino sketch includes the Ethernet library, this is the shield it was written for.
Key features and specs:
- WIZnet W5100 Ethernet controller
- RJ45 connector and microSD card slot
- Plugs onto an Uno or Mega
- Uses pins 10 to 13 (SPI) and pin 4 (SD card)
- Works with the standard Arduino Ethernet library
- Replaced by the Ethernet Shield 2
Arduino GSM Shield
Photo: Arduino.
The GSM Shield connected an Arduino to a mobile network, using a SIM card from a carrier that supported GPRS. With it, a project could send and receive text messages, make and receive voice calls (with an external speaker and microphone circuit), and connect to the internet over the slow cellular network of the day.
GSM networks have been shut down in many countries, so the shield has little use today. Arduino's own suggestion was the MKR GSM 1400, which is also discontinued now. For cellular projects today, look at boards with LTE support such as the MKR NB 1500.
Key features and specs:
- GSM and GPRS cellular modem on a shield
- SIM card slot, text messages and voice calls
- Plugs onto an Uno or Mega
- Uses pins 2, 3, and 7 (and the serial pins)
- Retired, replaced by the MKR GSM 1400
Arduino GSM Shield Pin Use
Pinout: Arduino.
Arduino WiFi Shield
Photo: oomlout, CC BY-SA 2.0, via Wikimedia Commons.
The original WiFi Shield added a wireless network connection to an Uno or Mega, plus a microSD card slot. It worked with the standard WiFi library, which meant a project could join a home network, serve a page, or send data online.
It used several pins for its own communication (including the SPI pins and pin 10), so those were not free for your own use. It was replaced by the WiFi Shield 101, and today most boards have WiFi built in.
Key features and specs:
- 802.11b/g WiFi shield with microSD card slot
- Plugs onto an Uno or Mega
- Uses the SPI pins and pin 10 for communication
- Works with the Arduino WiFi library
- Replaced by the WiFi Shield 101
Arduino WiFi Shield Pin Use
Pinout: Arduino.
Arduino WiFi Shield 101
Photo: Arduino.
The WiFi Shield 101 was a more modern IoT shield, developed with Atmel, with a built-in crypto chip for secure connections. Connecting to a network took only the network name and password, and a simple library handled the rest.
It worked with the Uno, the 101, the Zero, and the Mega, although it used up part of each board's memory, so it worked best on the larger boards. It is retired now, and the MKR WiFi 1010 and Uno R4 WiFi have WiFi built in.
Key features and specs:
- Atmel WiFi module with crypto-authentication
- Plugs onto Uno, 101, Zero, and Mega boards
- Easy-to-use library: only the network name and password are needed
- Secure connections through a crypto chip
- Retired, replaced by boards with built-in WiFi
Arduino USB Host Shield
Photo: Arduino.
The USB Host Shield lets an Arduino act as the host of a USB connection, the way a computer does. That means you can plug in devices like keyboards, mice, gamepads, flash drives, or Android phones and have your sketch talk to them. It is built around the MAX3421E, a chip that handles the USB side.
It runs at 5V and is TinkerKit compatible. It has been retired, but the Leonardo and newer boards can act as a USB device on their own, and the Mega ADK had a similar host port for Android phones.
Key features and specs:
- USB host controller: Maxim MAX3421E
- Connects keyboards, mice, gamepads, flash drives, and more
- Plugs onto an Uno or Mega, 5V operating voltage
- Up to 500 mA when powered externally, 400 mA from USB
- TinkerKit compatible
Arduino Wireless SD, Wireless Proto, and XBee Shields
Photo: Arduino.
These shields added a radio to an Arduino using XBee modules from Digi (originally MaxStream). An XBee is a small radio module that can talk to other XBees up to about 100 feet indoors or 300 feet outdoors with a clear line of sight. It can replace a serial or USB cable, or be put into a command mode and configured for broadcast and mesh networks.
The Wireless SD Shield added a microSD slot as well, and the Wireless Proto Shield added a prototyping area. All three are retired. Be aware that the shield's serial pins are shared with USB, so a switch lets you choose between uploading and using the radio.
Key features and specs:
- Socket for an XBee module (or similar footprint)
- About 100 ft indoors and 300 ft outdoors with line of sight
- Replaces a serial or USB cable, supports mesh networking
- Wireless SD version adds a microSD slot
- Wireless Proto version adds a prototyping area
- Switch selects between USB and the radio
Arduino Lucky Shield
Photo: Arduino.
The Lucky Shield packed a collection of sensors into a single shield, so you could try many ideas without wiring anything. It could read barometric pressure, humidity, temperature, light, motion, and presence, and it also had a relay, a buzzer, and a joystick.
You could use it as a simple controller and drive a small OLED display. It was open-source hardware, with its schematics published. It has been retired, and the Modulino nodes are the modern way to get the same mix of sensors.
Key features and specs:
- Bosch BME280 sensor: pressure, humidity, and temperature
- PIR motion sensor and an ambient light sensor
- 3-axis magnetometer and 3-axis accelerometer
- Omron relay, buzzer, and a 5-direction joystick
- Support for a small OLED display
- Open-source hardware
Arduino Yún Shield
Photo: Arduino.
The Yún Shield gave other Arduino boards the Yún's Linux side. Plugged onto an Uno or a Leonardo, it added WiFi, Ethernet, and a Linux processor running Linino OS, and the Bridge library let your sketch hand work to it. That meant a simple board could suddenly fetch web pages and run scripts.
It was sold as the Genuino Yún Shield. Retired now, it has been replaced by boards with their own built-in connectivity.
Key features and specs:
- Adds WiFi, Ethernet, and a Linux processor (Linino OS)
- Works with Uno, Leonardo, and similar boards
- Uses the Bridge library to share work with the sketch
- Sold as the Genuino Yún Shield
- Retired
Arduino Basic Kit
Photo: Arduino.
The Arduino Basic Kit was a starter kit developed in collaboration with Autodesk. It included the parts for simple projects, such as LEDs, sensors, and resistors, along with online access to 15 step-by-step tutorials that taught how to turn an idea into a working project.
It has been replaced by the Starter Kit R4 and the Plug and Make Kit. If you inherit a Basic Kit box, the components are still usable, and the tutorials are a good introduction.
Key features and specs:
- Developed in collaboration with Autodesk
- Online access to 15 step-by-step tutorials
- Components for simple projects with sensors and outputs
- Retired, replaced by the Starter Kit R4
Arduino Proto Extension Kit and Mega Proto Kit
Photo: Arduino.
These two kits were bare prototyping shields for people who wanted to build their own circuit on top of an Arduino. The Proto Extension Kit was for the Uno and similar boards, and the Mega Proto Kit Rev3 was for the Mega. Each came as a blank circuit board with pin headers and a few parts, and you soldered your own circuit onto it.
The Mega Proto Kit contents were the bare shield, a 40-way and an 18 by 2-way pin header strip, two pushbuttons, five 220 ohm, five 1K ohm, and five 10K ohm resistors, and three LEDs. The Arduino board itself was not included. They are retired, but proto shields are still a useful way to make a project permanent.
Key features and specs:
- Blank proto shield with connections to every I/O pin
- Pin headers, two pushbuttons, three LEDs, and resistors
- Space for through-hole and surface-mount parts
- Proto Extension Kit for the Uno, Mega Proto Kit Rev3 for the Mega
- Arduino board not included
Arduino IoT Prime Bundle
Photo: Arduino.
The IoT Prime Bundle was made with the distributor Distrelec. It was a starter kit for connecting things to the cloud: the box held an MKR WiFi 1010, an MKR ENV Shield for environmental sensors, an MKR Relay Shield for switching devices, and a bag of small components.
The idea was to read data and control real electrical devices from the Arduino Cloud. It is retired, but the same boards are sold separately and combine in the same way.
Key features and specs:
- Made with the distributor Distrelec
- MKR WiFi 1010 board
- MKR ENV Shield and MKR Relay Shield
- Small components for building IoT experiments
- Read data and control devices from the Arduino Cloud
- Retired
Wrap-Up and What's Next
That is every board, shield, and kit on the list, plus a look back at the retired ones. If you are still unsure which one to buy, go back to Part 2, where the decision guide matches boards to the kinds of projects you might build. If you already have a board in hand, the next article in the series is Part 3, where we start programming it: how a sketch runs, the core functions you will use constantly, and how to bring in libraries.
Up Next: Part 3: Programming Arduino, Sketches, Core Functions, and Libraries
Now that you have met the boards, Part 3 covers what to do with one: how a sketch actually runs, the core functions you will use in almost every project, how to install and manage libraries, and a simple debugging routine using the Serial Monitor.
