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Arduino: Standard project pin-out usage [2009-03-13]

Overview

Default Arduino pin-out usage shared amongst modular examples to allow them to work together.

Pin number	I/O	PWM	Description	Timer
Analog 0	In		Accelerometer X
Analog 1	In		Accelerometer Y
Analog 2	In		Accelerometer Z
Analog 3	In		Potentiometer 1
Analog 4	In		Potentiometer 2
Analog 5	In		Light Dependent Resistor
Digital 0	In		Serial Receive
Digital 1	Out		Serial Transmit
Digital 2	Out		LCD Clock signal (3-wire interface using MC14094 8-bit shift/latch)
Digital 3	Out	Yes	LED Red	Timer 2
Digital 4	Out		LCD Data signal (3-wire interface using MC14094 8-bit shift/latch
Digital 5	Out	Yes	LED Green	Timer 0
Digital 6	Out	Yes	LED Blue	Timer 0
Digital 7	Out		LCD Strobe signal (3-wire interface using MC14094 8-bit shift/latch
Digital 8	In		Control button for LCD menu / command
Digital 9	Out	Yes	Relay output 1 or Servo motor 1	Timer 1
Digital 10	Out	Yes	Relay output 2 or Servo motor 2	Timer 1
Digital 11	Out	Yes	Relay output 3 or Servo motor 3	Timer 2
Digital 12	In / Out		1-wire bus (temperature sensor) or CANBus
Digital 13	Out		Status LED

Save PWM outputs for those things that can really use PWM.
For cheap LCD display, use minimal 3-wire interface and only consume 3 Arduino pins, not 6 or more.

You can get a Serial LCD display, requiring only a single Arduino pin, but they are more expensive.