Every Arduino Leonardo pin with its capabilities (digital, PWM, ADC, I2C, SPI, UART) and the wiring gotchas that bite. An UNO-shaped board whose chip has native USB — it can pretend to be a keyboard, mouse or game controller. Great for HID projects.
ATmega32u4 @ 16 MHzLogic: 5 VPro in app
Arduino Leonardo pinout diagram
ICSP (2x3) on the bottom edge carries the 32U4's SPI. Download SVG
Pin
Capabilities
Watch out
D0 (RX1)
DigitalUART1 RXInterrupt
Serial1 header pins, not the USB serial
D1 (TX1)
DigitalUART1 TXInterrupt
Serial1 header pins, not the USB serial
D2 (SDA)
DigitalI2C SDAInterrupt
I2C here, not A4
D3 (SCL)
DigitalPWMI2C SCLInterrupt
I2C here, not A5
D4
DigitalAnalog in (A6)
D5
DigitalPWM
D6
DigitalPWMAnalog in (A7)
D7
DigitalInterrupt
D8
DigitalAnalog in (A8)
D9
DigitalPWMAnalog in (A9)
D10
DigitalPWMAnalog in (A10)SPI SS (soft)
D11
DigitalPWM
D12
DigitalAnalog in (A11)
D13
DigitalPWMBuilt-in LED
No SPI SCK here — SPI is on the ICSP header only
A0
Analog inDigital
A1
Analog inDigital
A2
Analog inDigital
A3
Analog inDigital
A4
Analog inDigital
A5
Analog inDigital
AREF
Analog reference
Call analogReference(EXTERNAL) before feeding a voltage in
IOREF
Power out 5V
Logic-level reference for shields — output only
RESET
Reset
Active LOW
5V
Power out 5V
3.3V
Power out 3.3V
VIN
Power in 7–12V
GND
Ground
Arduino Leonardo gotchas & notes
Native USB (the Keyboard and Mouse libraries work): the board can type or move the cursor on your PC.
I2C is on D2 (SDA) / D3 (SCL) — different from the UNO's A4/A5.
USB serial is 'Serial'; the TX/RX header pins are a separate 'Serial1'.
PWM on ~3, 5, 6, 9, 10, 11, 13.
SPI (MISO/MOSI/SCK) is ONLY on the ICSP header — not on D11–D13 like the UNO. Shields that take SPI from D11–D13 will not work; ones that use ICSP will.
External interrupts on 0, 1, 2, 3 and 7. Extra analog inputs A6–A11 live on D4, D6, D8, D9, D10, D12.
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