What am I missing here?
kikitsu:
What am I missing here?
"Voltage Regulator"
Yes there is a on-board +5vdc regulator that takes any external voltage 7-12vdc applied to the external voltage connector or the Vin shield pin and supplies the arduino with the +5vdc Vcc voltage it requires. The USB connector is another way to power the board via the +5vdc included in the USB connection. If there is both USB and external power avilable at the same time a on board voltage selection function uses the external power and cuts off the USB power.
Lastly those small rectangular 9 volt batteries are a very poor choice to power an arduino board. They provide pretty low maximum current capacity and have pretty poor battery duration (mAH rating) and cost a fortune per energy supplied. They are designed to power smoke alarms for several years not an arduino for a day or so.
Lefty
Why does a 9V battery power a 5V Arduino?
Some people have a lot of money.
This means that while a 9V battery can power an Arduino, you should not do it. This is because the battery current capacity is so low that they do not last very long.
@ dhenry Are You Bragging?
Bob