I recently purchased an Arduino Uno. After playing with it for a few days I decided to run my LED blinking project
in a stand-alone mode. I read the power requirement specification for the Uno online at http://arduino.cc/en/Main/ArduinoBoardUno
. It says any voltage between 6 and 20 volts as Vin will work. 7 to 12 volts is highly recommended. I hunted down a few wall-wart power supplies. I first found a 12Vdc 1.2A supply with the exact adapter plug.(what luck!) I hooked it up and like any good hack, I whipped out the Fluke and measured the on-board supply voltages. Here's what I found:
Vin: 14.47 Vdc
+5V: 4.98 Vdc3V3: 4.7Vdc !!!
WTF? (What the Fluke)
I unplugged it and hooked up choice wall-wart #2 which was a 9 Vdc 300mA RS special. (RS is a registered trademark of Tandy Corporation)
+5V: 4.98 Vdc
It looks like there may
be a 3.3Vdc regulation problem when Vin is above +12 Vdc.