Learning Goals 5 min
Welcome to Level 4. For three levels you've treated "Arduino" as one board — the UNO R3. The real Arduino family is a dozen boards spanning $5 microcontrollers to $80 IoT devices. The certification exam expects you to know them. By the end of this lesson you will be able to:
- Name the main boards in the official Arduino family (UNO, Mega, Nano, MKR, Nano 33 BLE, Portenta) and roughly when to choose each.
- Identify the four properties that distinguish boards: processor, memory, radios, operating voltage.
- Spot the three biggest "UNO-shaped but different" gotchas: 3.3 V logic, native USB instead of FTDI, and different pinouts despite the same form factor.
Warm-Up 10 min
Lay out whatever Arduino-shaped boards you have. Likely candidates:
- UNO R3 — the original.
- Maybe a UNO R4 WiFi (the 2023 update with an ESP32-S3 co-processor).
- Nano (cheap clones often labelled "Nano V3").
- Nano 33 BLE / Nano 33 BLE Sense (from L03-26).
- An ESP-based board you used in L03-29..38 (NodeMCU, ESP32 DevKit).
Two quick questions
- What's the highest voltage you should ever apply to a UNO R3 GPIO pin? What about a Nano 33 BLE?
- You wrote a sketch using
analogRead(A0)on UNO. Will it return the same numbers if you upload to a Nano 33 BLE?
Reveal
- UNO R3 = 5 V. Nano 33 BLE = 3.3 V. Plug 5 V into a Nano 33 BLE's pin and you may damage the chip.
- No. UNO's ADC is 10-bit (0..1023); Nano 33 BLE's default is also 10-bit but the chip supports 12-bit (0..4095) and the voltage reference is 3.3 V instead of 5 V. So a pot reading "512" on UNO is reading "half of 5 V"; on a Nano 33 BLE it's "half of 3.3 V". Same number, different physical voltage.
New Concept · The board lineup 25 min
The official Arduino families
| Board | Chip | Voltage | RAM / Flash | Radio | Use for |
|---|---|---|---|---|---|
| UNO R3 | ATmega328P | 5 V | 2 KB / 32 KB | — | Learning, hobby, robust |
| UNO R4 Minima | RA4M1 (32-bit ARM) | 5 V (3.3 V GPIO option) | 32 KB / 256 KB | — | UNO drop-in upgrade, more memory |
| UNO R4 WiFi | RA4M1 + ESP32-S3 | 5 V | 32 KB / 256 KB | WiFi + BLE | UNO-shape with internet |
| Mega 2560 | ATmega2560 | 5 V | 8 KB / 256 KB | — | Lots of GPIO (54 + 16 analog) |
| Nano (V3) | ATmega328P | 5 V | 2 KB / 32 KB | — | Tiny breadboard-friendly UNO |
| Nano 33 BLE | nRF52840 | 3.3 V | 256 KB / 1 MB | BLE | BLE projects, low power |
| Nano 33 BLE Sense | nRF52840 + 9 sensors | 3.3 V | 256 KB / 1 MB | BLE | Edge AI, wearables |
| Nano ESP32 | ESP32-S3 | 3.3 V | 512 KB / 4 MB | WiFi + BLE | Modern small WiFi board |
| MKR WiFi 1010 | SAMD21 + NINA W102 | 3.3 V | 32 KB / 256 KB | WiFi + BLE | MKR-family IoT projects |
| Portenta H7 | STM32H747 (dual-core Cortex-M7+M4) | 3.3 V | 1 MB / 2 MB + external | WiFi + BLE | Industrial / pro, runs OpenMV, MicroPython |
The lineup splits into three eras:
- Classic AVR (UNO, Nano, Mega): 8-bit, 5 V, simple, robust. The learning standard.
- Modern 32-bit (Nano 33 BLE, MKR, UNO R4, Nano ESP32): ARM or RISC-V, 3.3 V, much more memory, radios on board.
- Pro (Portenta, Opta): industrial form factors, dual-core, video / Ethernet / industrial bus support.
The four properties that matter
- Processor: 8-bit AVR vs 32-bit ARM/RISC-V. 32-bit is faster and can run bigger libraries (TensorFlow Lite, OpenCV); 8-bit is more power-efficient and forgiving.
- Memory: RAM (working memory, < 1 ms) and Flash (program memory, persistent). 2 KB RAM is tight for anything with a web server; 256 KB RAM runs a small operating system.
- Radios: WiFi, BLE, Bluetooth Classic, LoRa, sub-GHz. Built-in vs add-on shield. Adds cost but removes wiring.
- Operating voltage: 5 V for AVR; 3.3 V for everything modern. A 5 V signal into a 3.3 V GPIO can damage the chip.
The three biggest UNO-shaped gotchas
- 3.3 V GPIO. The UNO R4 still has a 5 V supply rail but its GPIO can be configured 3.3 V. Many newer "UNO shape" boards (Arduino UNO R4 WiFi, Adafruit Metro M0) are 3.3 V GPIO. Old 5 V shields might still work if their inputs accept 3.3 V; old 5 V outputs into your board damage it.
- Native USB. Modern boards use the main chip's native USB instead of a separate USB-serial chip. Different reset behaviour (no auto-reset on serial connect on some), and they can present as USB HID, mouse, keyboard, MIDI.
- Different pinouts. The Mega's I²C pins are 20/21 not A4/A5. The MKR boards don't expose every GPIO on labelled pins. Always check the pinout diagram before connecting.
Worked Example · Pick a board for three real briefs 20 min
Brief 1 — "A wearable that detects when I wave and lights an LED"
Requirements: low power (battery), tiny, BLE optional, accelerometer, runs on a coin cell for hours.
Reveal one good choice
Nano 33 BLE Sense. Built-in IMU + microphone + low power + small form factor. With deep sleep, runs on a CR2032 coin cell for days. BLE for phone control if you want.
A UNO would also work in theory, but: no IMU on board, ~50 mA active = hours not days on coin cell, no BLE.
Brief 2 — "A web-controlled lamp running for years on mains power"
Requirements: WiFi, robust, lots of free memory, OTA updates nice-to-have.
Reveal one good choice
Nano ESP32 (modern, plenty of RAM, WiFi + BLE, USB-C) OR UNO R4 WiFi (UNO-shaped, drop-in for school projects, internet built-in). Both fine.
Avoid: plain UNO R3 with a separate WiFi shield — works but expensive and clunky. Avoid: Portenta H7 — overkill, 5× the price.
Brief 3 — "Replace 30 control wires with a single chassis with lots of GPIO"
Requirements: many digital inputs / outputs, no radio, lots of analog channels too.
Reveal one good choice
Mega 2560. 54 digital + 16 analog + 4 hardware UARTs. Direct UNO drop-in for code; just "way more pins". The right board for industrial fixtures, big LED matrices, organ-style instrument controllers.
Pattern in all three answers
The choice flows from the brief, not from the hype:
- List the must-haves (radio, voltage, GPIO count, memory).
- Filter the table from §3.
- Pick the cheapest board that meets the must-haves.
Try It Yourself · Five board-picking questions 15 min
A sketch declares char buffer[3000]. Will it fit on UNO R3 RAM? On Nano 33 BLE?
Reveal
UNO R3 RAM = 2 KB = 2048 bytes. 3000 won't fit. Nano 33 BLE = 256 KB. Fits 80× over.
You connect a 5 V sensor to a Nano 33 BLE's A0. The sensor outputs 0–5 V. What happens?
Reveal
The Nano 33 BLE's GPIO is rated for max ~3.6 V. Direct connection can damage the input. Use a resistor divider (e.g. 1k + 2k) to scale 0–5 V → 0–3.3 V.
You want a single board with WiFi, BLE, USB-C, and 3 hardware UARTs. Which Arduino?
Reveal
Nano ESP32 fits all four. ESP32-S3 has built-in USB-C, WiFi, BLE, and 3 UARTs.
You need to read a sensor with sub-degree precision via its 0–3.3 V output. UNO ADC is 10-bit; Nano 33 BLE can be configured 12-bit. What's the resolution difference?
Reveal
10-bit: 1024 steps over 3.3 V = ~3.2 mV/step. 12-bit: 4096 steps over 3.3 V = ~0.8 mV/step. 4× finer resolution on the Nano 33 BLE.
An industrial project needs to run a small TensorFlow model on live camera frames at 15 fps. What Arduino-family board fits, and what doesn't?
Reveal
Portenta H7 fits — dual-core M7+M4, 1 MB RAM, runs OpenMV for camera, MicroPython, TFLite Micro. Nano 33 BLE Sense can do TFLite Micro but not at video frame rates (no camera, only mic + IMU). UNO / Nano can't — RAM way too small, no float performance.
Mini-Challenge · Pick boards for your saved projects 10 min
- List 5 of your L1–L3 sketches.
- For each, identify what made the UNO good enough (or not).
- For any project where UNO struggles, name the upgrade board and the specific reason.
Reveal a likely list
- L01-22 Reaction Timer: UNO fine. Tiny memory, no radio, no clock needed.
- L02-43 Weather Station v2: UNO + SD card works but RAM is tight. Nano 33 BLE or Nano ESP32 for more RAM + WiFi reporting.
- L03-28 BT Car: UNO fine for HC-05; Nano 33 BLE for the iOS-compatible BLE upgrade.
- L03-34 WiFi Lamp: UNO can't do WiFi alone. ESP8266 / ESP32 / Nano ESP32 / UNO R4 WiFi.
- L03-44 Plant Monitor: ESP-class board for the WiFi + dashboard. Low power = ESP32 with deep sleep (L04-37).
Recap 5 min
The Arduino family is ~10 boards across three eras. Pick by listing requirements (voltage, GPIO count, memory, radio) and matching to the cheapest qualifying board. 5 V UNO-shaped boards are not always 5 V; modern boards are 3.3 V GPIO. Memory matters more than people think. Tomorrow we make this systematic — a board-picking checklist.
- Microcontroller
- A small all-in-one chip with CPU + memory + peripherals + GPIO. Arduino boards are essentially convenient packaging around microcontrollers.
- AVR vs ARM vs RISC-V
- Processor architectures. AVR = original 8-bit Atmel (UNO, Mega). ARM = 32-bit (Nano 33 BLE, MKR, Portenta). RISC-V = newest open architecture (some ESP32 variants).
- Flash / RAM
- Flash = program storage, persistent, KB to MB. RAM = working memory, volatile, KB to MB. Sketches need both.
- 3.3 V vs 5 V logic
- The voltage that represents "HIGH". Mixing without a level shifter risks damage on the lower-voltage chip.
- Native USB
- USB built into the main chip, not a separate USB-serial converter. Lets the board be a HID device (keyboard, mouse, MIDI), faster, but different reset behaviour.
- Form factor
- The physical shape + pin arrangement: UNO shape, Nano shape, MKR shape. Sometimes interchangeable for shields, sometimes not.
- Shield
- An add-on board that plugs into another Arduino's headers. UNO-shaped shields work on most UNO-shaped boards but pinouts may differ.
- Co-processor
- A second chip handling specific functions (e.g. ESP32-S3 for WiFi on UNO R4 WiFi). Keeps the main chip simple.
Homework 5 min
- Make a one-page reference: every Arduino-family board with its key specs. Tape it inside your notebook.
- For each board you own, record its model, USB-serial chip, default voltage, key radios.
- Read ahead to ARD-L04-02 (Choosing the Right Board). Tomorrow we make the choice systematic.
Bring back next class:
- Your board reference card.
- Boards inventory.