Arduino Nano Guide

An Arduino Nano shows up in prototypes and small assemblies where a full-size Uno will not fit on the bench or inside the enclosure. Before wiring a Nano into a project, an engineer needs to understand the pin functions and power inputs. Version identification also matters because the Nano family now includes boards with different processors and logic levels.

This guide uses the classic Arduino Nano, the original ATmega328P board, as the baseline for pinout and power. Later sections cover the newer Nano Every, Nano ESP32, and Nano R4 boards, and note where their pin functions or operating voltage diverge from the classic layout.

Key Takeaways

• The classic Arduino Nano packs an ATmega328P processor and 8 analog inputs into a 45 x 18mm breadboard-friendly footprint.
• A Nano draws power from USB, VIN, or a regulated 5V pin, and each path has its own voltage limits and failure points.
• The Nano Every, Nano ESP32, and Nano R4 share the classic form factor but differ in processor and logic voltage, so they are not automatic drop-in replacements.

Classic Arduino Nano Specifications

What Is an Arduino Nano?

The Arduino Nano is a compact, breadboard-friendly development board built around a microcontroller and the circuitry needed to run it: a voltage regulator, a USB-to-serial interface, and reset circuitry. Where the Uno spreads the same core electronics across a full-size PCB with a barrel jack and USB-B connector, the Nano fits it onto a card small enough to plug directly into a breadboard.

Arduino Nano vs. Uno

The size difference matters more than it looks: a Nano's pins sit on 0.1-inch centers along both long edges, so the board straddles a breadboard's center channel with every pin individually accessible. For a closer look at the larger board, see Flux's Arduino Uno schematic diagram and Arduino Uno beginner's guide. Or, for a broader comparison of Arduino board sizes and capabilities, see how the Arduino Mega, Micro, and Uno differ.

Arduino Nano Pinout and Pin Functions

The classic Arduino Nano exposes 30 pins across two rows for digital I/O, analog input, and dedicated communication interfaces. Each pin group has a distinct role in a schematic, and mixing them up is a common wiring mistake on a first build. Arduino publishes an official pinout diagram alongside the datasheet; the table below covers the same ground for quick reference.

SPI and the onboard LED both use D13, so a device wired to D13 for SPI communication makes the LED flicker during transfers, which is worth remembering when an SPI peripheral seems to work only intermittently.

Keep in mind that pin functions are not identical across the Nano family.

• The Nano ESP32 runs 3.3V logic, is not 5V tolerant on its GPIO pins, and replaces the 5V pin with VBUS.
• The Nano R4 keeps 5V logic but adds a CAN bus and a 12-bit DAC the classic board lacks.

Confirm the pinout diagram for the exact board in hand before reusing a schematic built for a different Nano version.

How to Power an Arduino Nano

A Nano accepts power from three places: the USB connector, the VIN pin, and the 5V pin, and the board automatically selects whichever source supplies the higher voltage. Understanding each path prevents the handful of mistakes that damage more Nano boards than any other wiring error.

Power Input Options

• USB: regulated 5V, limited to roughly 500mA by an onboard polyfuse.
• VIN: unregulated 7-12V (6-20V limit) feeding the onboard regulator, which steps it down to 5V.
• 5V pin: a regulated 5V input that bypasses the regulator, or an output when powered from USB or VIN.
• 3.3V pin: a secondary regulator output, good for up to about 50mA.

VIN and the 5V pin are not interchangeable. VIN expects unregulated voltage above 5V, since it still passes through the onboard regulator. The 5V pin sits after that regulator and needs an already-regulated source; it will not tolerate the higher voltages VIN accepts.

Common Arduino Nano Power Mistakes

• Feeding regulated 5V into VIN: falls below the regulator's dropout voltage, leaving the board under-powered and unreliable.
• Exceeding the regulator's output current: it dissipates the VIN-to-5V difference as heat, so a high VIN with a current-hungry load can overheat it well below rated output.
• Powering external components from 5V or 3.3V: motors and relays need their own supply; the onboard regulator is sized for light peripheral loads.
• Connecting 5V signals to a 3.3V Nano variant: the Nano ESP32 needs a level shifter for any sensor built around the classic Nano's 5V logic.
• Combining supplies without isolation: VIN and USB together is fine, since the board picks the higher source, but two regulated supplies tied to the 5V pin risk a current fight.

Arduino Nano Versions Compared

Four boards currently carry the Nano name, and they share a footprint more than they share silicon. Matching the processor, logic voltage, and memory to the project matters more than matching the board's shape.

Pin compatibility stops at the physical footprint. All four boards share the same 30-pin layout and 0.1-inch spacing, so a carrier PCB designed for one physically accepts any of them. Electrical compatibility is separate: a shield built for the classic Nano's 5V logic can damage a Nano ESP32's 3.3V GPIO pins, and code written for the classic Arduino Nano's pin assignments needs an adjusted board definition before it runs on the ATmega4809 or RA4M1 boards. The AVR-based boards run simpler 8-bit instruction sets, while the ESP32 and R4 use 32-bit cores that handle heavier code faster.

Choosing a Nano Version

• Classic compatibility, lowest cost: the original Nano, for reproducing an existing 5V design.
• More memory, same voltage: the Nano Every, once sketches outgrow 2KB of SRAM.
• Wireless connectivity: the Nano ESP32, for Wi-Fi or Bluetooth without a separate radio module.
• 32-bit processing, extra peripherals: the Nano R4, for CAN bus, a built-in DAC, or headroom beyond 8-bit AVR.
• Low idle power draw: the classic Nano, or an ESP32 board's deep-sleep modes if wireless is still needed.

Using Arduino Nano in Projects and Custom PCBs

A Nano moves through several stages between a first prototype and a finished product, and each stage changes how the board should be mounted. Breadboard prototypes use the header pins directly. Permanent assemblies often solder wires straight to the board or use a socketed carrier that stays swappable for repairs. Custom PCB projects mount the Nano as a module, either socketed or soldered flush with castellated edges.

Design Considerations for a Nano Carrier Board

• Schematic placement: place the Nano as one schematic symbol rather than redrawing the ATmega328P, and verify every symbol pin maps to the correct physical pin.
• Header spacing and orientation: match the 0.1-inch pitch and keep the USB connector and reset button on an accessible edge.
• USB connector access: leave clearance around the connector (Mini-B, Micro-USB, or USB-C) so a cable can seat without hitting an enclosure wall.
• Reset-button access: add a cutout or external reset button if the onboard one will be covered once mounted.
• Power and decoupling: add a bulk capacitor near VIN and a bypass capacitor near the 5V and 3.3V pins.
• Mechanical clearance: check the USB connector and crystal height against anything mounted directly above.
• Antenna clearance: on the Nano ESP32, keep copper pours and shielding away from the module's antenna area.

Flux supports each step directly:

Bringing an Arduino Nano into Your Next PCB

An Arduino Nano earns its place in a design once the pinout, power path, and version are locked in. From there, the remaining work is turning a breadboard prototype into a board that survives outside the lab. Flux keeps that transition in one place: a shared component library for the Nano module, footprint validation, and DFM review before a carrier PCB goes to fabrication. Start a Nano-based PCB project in Flux.

FAQs

What is an Arduino Nano used for?

Is the Arduino Nano a 5V or 3.3V board?

What is the difference between Arduino Nano and Uno?

Can an Arduino Nano replace an Arduino Uno?

How do you power an Arduino Nano?

Do all Arduino Nano boards have the same pinout?

Which Arduino Nano version should I use?