Every Arduino Nano pin with its capabilities (digital, PWM, ADC, I2C, SPI, UART) and the wiring gotchas that bite. An UNO on a breadboard-friendly stick. Same chip and 5 V logic, plus two extra analog-only inputs (A6/A7).
ATmega328P @ 16 MHzLogic: 5 VFree in app
Arduino Nano pinout diagram
ICSP (2x3) at the far end: MISO · 5V · SCK · MOSI · RST · GND. Download SVG
Pin
Capabilities
Watch out
D0 (RX)
DigitalUART RX
Shared with USB serial
D1 (TX)
DigitalUART TX
Shared with USB serial
D2
DigitalInterrupt
D3
DigitalPWMInterrupt
D4
Digital
D5
DigitalPWM
D6
DigitalPWM
D7
Digital
D8
Digital
D9
DigitalPWM
D10
DigitalPWMSPI SS
SS is convention, not hardwired — any output pin can be chip select. But keep D10 an OUTPUT whenever SPI is master, or the hardware drops into slave mode
D11
DigitalPWMSPI MOSI
D12
DigitalSPI MISO
D13
DigitalSPI SCKBuilt-in LED
The L LED loads this pin; also on the ICSP header
A0
Analog inDigitalpin 14 in code
A1
Analog inDigitalpin 15 in code
A2
Analog inDigitalpin 16 in code
A3
Analog inDigitalpin 17 in code
A4
Analog inDigitalI2C SDApin 18 in code
Using it as GPIO takes out I2C
A5
Analog inDigitalI2C SCLpin 19 in code
Using it as GPIO takes out I2C
A6
Analog in only
Cannot be a digital pin
A7
Analog in only
Cannot be a digital pin
AREF
Analog reference
Call analogReference(EXTERNAL) before feeding a voltage in, or it shorts against the internal reference
RST
Reset
Active LOW — pull to GND to reset
5V
Power out/in 5V
3V3
Power out 3.3V
Weak — from USB chip, ~50 mA
VIN
Power in 7–12V
GND
Ground
Arduino Nano gotchas & notes
A6 and A7 are ANALOG-INPUT ONLY — they can't be used as digital pins.
A0–A5 double as digital pins 14–19: write 14 (or A0) in a sketch, not D14 — that name isn't defined on AVR boards. A4/A5 included, but using them as GPIO takes out I2C.
I2C on A4 (SDA) / A5 (SCL); SPI on D10–D13; PWM on ~3, 5, 6, 9, 10, 11.
External interrupts (attachInterrupt) are only on D2 (INT0) and D3 (INT1); every other I/O pin supports pin-change interrupts (PCINT) via the PCICR/PCMSK registers or a library.
ICSP header (2x3) at the end of the board: MISO, MOSI, SCK, RESET, 5V, GND — same SPI lines as D11–D13, used to burn the bootloader.
Power it from 5 V on the 5V pin, or 7–12 V on VIN; the onboard 3V3 is weak (from the USB chip).
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