It is almost always better to add a schematic to your question. Backwards engineering from a picture can be confusing at time and lead to incorrect assumptions.

What you want to do appears to be possible. It looks like you are injecting 9 Volts positive at VIN. Examining the Arduino Uno R3 schematic here we see the VIN net connected to the input pin 8 and also to the input side of the 5 Volt regulator (NCP1117ST50T3G). This distributes the 5 Volts to the Atmel processor (appears to power the LED directly) and to the external switch which is assumed to be normally open.

The total current needed by external devices connected to the Arduino Uno R3 5 Volt regulator should be considered. The NCP1117ST50T3G data sheet here state the regulator can handle in excess of 1 Amp.

Assuming a

  10Kohm pull up resistor connected to the external switch.

However, Alkaline 9 Volt battery only have about 550mAh while Alkaline AA 1.5 Volt batteries have about 2000mAh.. You would need 6 AA 1.5 Volt batteries in series to generate 9 Volts. But they should last about 4 times longer.

It is almost always better to add a schematic to your question. Backwards engineering from a picture can be confusing at times and lead to incorrect assumptions.

What you want to do appears to be possible. It looks like you are injecting 9 Volts positive at VIN (Pin 8 of the POWER header). Examining the Arduino Uno R3 schematic here we see the VIN net connected to the input Pin 8 of the POWER header and also to the input side of the 5 Volt regulator (NCP1117ST50T3G). This distributes the 5 Volts to the Atmel processor (appears to power the LED directly) and to the external switch which is assumed to be normally open but when closed connects to a 10Kohm resistor to ground.

The total current needed by external devices connected to the Arduino Uno R3 5 Volt regulator should be considered in such a design. The NCP1117ST50T3G data sheet here state the regulator can handle in excess of 1 Amp (or 1000mA).

Assuming the LEDs take at most 20mA each and a worse case of all LED in the on state, that is 6 x 20mA or 120mA. Also, when the switch is closed there is a current path from 5 Volts to ground through a 10Kohm resistor. Using V = A x R we see that A = V / R = 5 / 10000 = 0.5mA when the switch is closed. So the total current the external devices might use is likely no more than 120.5mA. This is far less than 1000mA (the upper limit of the Arduino's 5 Volt regulator) so appears well withing safety margins.

However, an Alkaline 9 Volt battery only contains about 550mAh. Ignoring the current it takes to run the Arduino Uno R3, we see that dividing the worst case external current demand of 120.5mAh into 550mAh we get 4.6 hours of use. An Alkaline AA 1.5 Volt battery contains about 2000mAh.. You would need 6 AA 1.5 Volt batteries in series to generate 9 Volts. But they should last about 4 times longer.

It is almost always better to add a schematic to your question. Backwards engineering from a picture can be confusing at time and lead to incorrect assumptions.

What you want to do appears to be possible. It looks like you are injecting 9 Volts positive at VIN. Examining the Arduino Uno R3 schematic here we see the VIN net connected to the input pin 8 and also to the input side of the 5 Volt regulator (NCP1117ST50T3G). This distributes the 5 Volts to the Atmel processor (appears to power the LED directly) and to the external switch which is assumed to be normally open.

10Kohm pull up resistor connected to the external switch.

However, Alkaline 9 Volt battery only have about 550mAh while Alkaline AA 1.5 Volt batteries have about 2000mAh.. You would need 6 AA 1.5 Volt batteries in series to generate 9 Volts. But they should last about 4 times longer.

It is almost always better to add a schematic to your question. Backwards engineering from a picture can be confusing at time and lead to incorrect assumptions.

What you want to do appears to be possible. It looks like you are injecting 9 Volts positive at VIN. Examining the Arduino Uno R3 schematic here we see the VIN net connected to the input pin 8 and also to the input side of the 5 Volt regulator (NCP1117ST50T3G). This distributes the 5 Volts to the Atmel processor (appears to power the LED directly) and to the external switch which is assumed to be normally open.

The total current needed by external devices connected to the Arduino Uno R3 5 Volt regulator should be considered. The NCP1117ST50T3G data sheet here state the regulator can handle in excess of 1 Amp.

Assuming a

10Kohm pull up resistor connected to the external switch.

However, Alkaline 9 Volt battery only have about 550mAh while Alkaline AA 1.5 Volt batteries have about 2000mAh.. You would need 6 AA 1.5 Volt batteries in series to generate 9 Volts. But they should last about 4 times longer.