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Topic: Choosing the power supply (Read 1 time) previous topic - next topic


I have an Arduino Uno and it's connected to both a 12v wall adapter via the jack socket as well as an android tablet via the USB. The tablet seems to be powering the Arduino as well as it's connected sensors, but I want the unlimited power available from the wall socket to be powering it (the Arduino + sensors are draining the battery on the tablet faster than it can charge)

I know on older versions of the Arduino there was a jumper to select which power source to use.

Does anyone know how to tell (force) the Arduino to draw its power from the wall supply instead of USB ?


I want the unlimited power energy available from the wall socket

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Your answer may already be here: https://forum.arduino.cc/index.php?topic=384198.0


I suppose technically it's not actually unlimited either. But thanks for your constructive response anyway


There's an automatic switch on recent boards.  If there's adequate voltage on the barrel jack, it wins.  You're good to go.


External power should be selected when Vin/2 >3.3V.
Vin is the voltage after the reverse polarity protection diode.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


Thanks for the reply CrossRoads.
So does that mean if Vin > 6.6v it should use the external power?
I have the board connected to both a 12v dc adapter and the USB cable (to communicate with an android app) but the board, sensors and LEDs definitely seems to be powered mainly (if not exclusively) by the USB and therefore draining the tablet's battery.
Any ideas why this would happen?


@ SeanJD

Can I offer 2 ideas ?

In 2011, I did a project using  Opto-couplers.  The Arduino board has it own power supply, and the other end - USB computer side has it own as well.  I was able to communicate with the Arduino and Computer using Processing. Do a search of the forum. 

Also you can do the same using RS232. USB to RS232 attach at the Tablet end, And a MAX232 at the Ardiuno end. That will take care of the communication part.

The power part with the 12 V, that have to provide to the Ardiuno and sensors.

Just 2 ideas.

I have 2 Android device. 1 tablet and a cell phones. Theses two devices don't have enough currents to power Arduino with sensors.  A lonely board... yes, but not a fully loaded board with sensors .... motors !!! no way !!! I don't want to damage my cell phone and my tablet.

@ CrossRoards

Nice to "see" you. Wrote a book ! Nice. 

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