The Iduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source. The FTDI FT232RL chip on the Nano is only powered if the board is being powered over USB. As a result, when running on external (non-USB) power, the 3.3V output (which is supplied by the FTDI chip) is not available and the RX and TX LEDs will flicker if digital pins 0 or 1 are high. Summary: Microcontroller : Atmel ATmega168 Operating Voltage (logic level) : 5 V Input Voltage (recommended) : 7-12 V Input Voltage (limits) : 6-20 V Digital I/O Pins : 14 (of which 6 provide PWM output) Analog Input Pins : 8 DC Current per I/O Pin : 40 mA Clock Speed : 16 MHz Dimensions : 0.73" x 1.70"