Arduino 小技巧 - 使用GPIO當作5V or GND的方法

有時候測試時沒有使用麵包版，
版子上又有多餘的GPIO時，若電流很小(例如驅動一般LED)，可以使用GPIO當作VCC/GND

以Leonardo為例，GPIO可以輸出40mA
http://arduino.cc/en/Main/ArduinoBoardLeonardo#.Uym72PmSyXo

Summary

Microcontroller	ATmega32u4
Operating Voltage	5V
Input Voltage (recommended)	7-12V
Input Voltage (limits)	6-20V
Digital I/O Pins	20
PWM Channels	7
Analog Input Channels	12
DC Current per I/O Pin	40 mA
DC Current for 3.3V Pin	50 mA
Flash Memory	32 KB (ATmega32u4) of which 4 KB used by bootloader
SRAM	2.5 KB (ATmega32u4)
EEPROM	1 KB (ATmega32u4)
Clock Speed	16 MHz

ex:
  pin8: 5V
  pin9: 0V

code:

  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);

  digitalWrite(8, HIGH);
  digitalWrite(9, LOW);