9v Battery - Arduino Uno R3 - PWR_SEL pins? Vin input - 5v output

What pair of PWR_SEL pins do I put a jumper on to use external power? I've got a 9volt battery clip with pos/neg wires. Do i plug directing into board's power connecters Vin/GND? After I've powered the board from an external source using Vin/GND, can I use the power connecters 5V/GND like most examples use? I understand the Vin pin as an input/output pin. I def don't want to fry my board. Thank You! XD

Are there RWR_SEL pins on an Arduino UNO R3 ?

After I've powered the board from an external source using Vin/GND, can I use the power connecters 5V/GND like most examples use?

: Yes!
I understand you supply +9V to Vin, Battery minus to GND, and can take +5V from the 5V pin
(assuming you do not take a too big current to fry the power regulator on the Arduino board)
If you need more amps @ 5V than the on board regulator can provide, you'll have to consider that something might be wrong in general, with your 9V battery design. ( A 12V wallwart and taking a big current from 5V or the output pins can become a problem )

I understand the Vin pin as an input/output pin

I understand it as an input.
5V can be output and input (input not recommended, however. see Chapter Power on this page: http://arduino.cc/en/Main/ArduinoBoardUno

Hi,
The board is very flexible in how you power it. If you have a supply greater than 7.5 volts, you can feed it in via the power jack or the vin/gnd pins, the on board regulator will drop this down to the 5 volts needed by the chip. This regulated five volts is also available through the 5v pin. You do not need to add any jumpers, the five volts line is simply the output of the regulator attached to vin.

Its also very useful that you can still use a USB connection for programming and serial communication when the UNO is powered through the regulator.

Lastly, 9v batteries are not a very good power source if you plan on running any other devices connected to the Arduino - check the two links in my signature for details.

Duane B

rcarduino.blogspot.com

encryptor:
What pair of PWR_SEL pins do I put a jumper on to use external power?

That isn't an UNO R3. It is a Diecimila.

( A 12V wallwart and taking a big current from 5V or the output pins can become a problem )

How is this a problem? I read that the max limit to input voltage is 20V.

encryptor:
( A 12V wallwart and taking a big current from 5V or the output pins can become a problem )

How is this a problem? I read that the max limit to input voltage is 20V.

The on-board regulator is linear and so it burns up more power with higher input voltages. The more power the regulator dissipates, the hotter it gets. The hotter the regulator gets, the less current output it can sustain. Since the PCB is the only heat sink, it limits the practical input voltage to about 12V. This is not a hard limit, but look what happens as you increase Vin.

Assume you want to draw 500mA on the 5V when powered through Vin.

9V:
Voltage Drop of Regulator = 9V - 5V = 4V
Power Dissipated: 4V * 500mA = 2W

12V:
Voltage Drop of Regulator: 12V - 5V = 7V
Power dissipated: 7V * 500mA = 3.5W

20V:
Voltage Drop of Regulator: 20V - 5V = 15V
Power dissipated: 15V * 500mA = 7.5W

There's no way the regulator will dissipate 7.5W without a proper heat sink. 2W is really pushing it even at 9V. And we see this problem from many people. Everything works fine when powered over USB but not so well when powered through Vin, because the regulator can't support that much current at high voltages.