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Arduino UNO R3 pinout

Every Arduino UNO R3 pin with its capabilities (digital, PWM, ADC, I2C, SPI, UART) and the wiring gotchas that bite. The classic beginner board. 5 V logic, forgiving, huge library support.

ATmega328P @ 16 MHzLogic: 5 VFree in app

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
D11	DigitalPWMSPI MOSI
D12	DigitalSPI MISO
D13	DigitalSPI SCKBuilt-in LED
A0	Analog inDigital
A1	Analog inDigital
A2	Analog inDigital
A3	Analog inDigital
A4	Analog inI2C SDA
A5	Analog inI2C SCL
5V	Power out 5V	Total board current limited by USB/regulator
3.3V	Power out 3.3V	Max ~150 mA
VIN	Power in 7–12V
GND	Ground

Arduino UNO R3 gotchas & notes

PWM (analogWrite) on pins marked ~: 3, 5, 6, 9, 10, 11.
I2C is shared with A4 (SDA) and A5 (SCL).
Pins 0/1 are the USB serial — avoid using them while Serial is active.

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