Power Arduino Uno and Adafruit Motor Shield V2 From Single AC/DC Converter

I’m a complete noob to electronics / Arduino … and this forum.

I am building an ‘art project’ that once installed, will be unattended. Consequently it needs to be idiot proof. Simplified description is: a rotating drum on a stand.

Part One.

I have an Arduino Uno and Adafruit Motor Shield v2. Motor(s) are powered via screw terminals on the motor shield. I would like to power the Arduino and the motor shield from the same DC (mains) power supply.

Part Two.

I would like to be able to switch the whole thing on / off at the mains. I don't want to use the socket as that may not be practical, I need a switch on the stand of the device. Somebody needs to turn this thing off at night and know its dead (and safe)


  1. Spec of the DC converter. Max voltage of both Arduino and motor shield is 12v. Max amperage of Arduino is 50mA (?) max amperage of motor shield is 3A. So power supply of 12v 3.05A (amps can be more as what I don't need wont be used) Correct?

NOTE: currently I am using a 12v 350mA stepper motor. This may change, my question is really concerned with the overall logic here.

  1. From what I have read, the best way to power the Arduino is via the DC socket? It would be more practical to use vin, is that possible - what’s the difference (socket has reverse diode) ?

  2. I can connect the Arduino and motor shield in parallel from the power supply as specified above? Correct ?

  3. I can switch power on / off to the whole setup by inserting a switch between the dc converter and the mains wall socket ( I know this is obvious, I’m checking for gotchas )

Link to Adafruit Motor Shield v2(apparently these aren't a thing here so I attached screen grabs also)


  1. A diagram
  2. Arduino spec screen grabbed from website
  3. Adafruit motor shield v2 spec grabbed from website
  4. Screen grab of motor driver chip datasheet.
  5. Stepper Motor datasheet

If you are still reading… any advice is appreciated !

Looks good. You will probably find a 12V 5A power supply very reasonable and they can be gotten in wall wart format. Taking the 12V to the VIN helps reduce the noise on the micro portion of the circuit because of the capacitors etc in the circuit. Also very important be sure the grounds are connected. The motor off thing should be one of the first things you do in your setup portion of your code. You may get a very short glitch on power up however I believe the low voltage detection in the driver will solve that. Be sure the motors are powered by the 12V supply.

Hi, thanks for your response. A clarification.

“You will probably find a 12V 5A power supply very reasonable and they can be gotten in wall wart format”

Power needs to come from a DC power supply inside the unit as the distance to the socket is variable / unknown. I omitted the switch in the diagram that I refer to in my question (updated and attached to this reply)

“Wall wart”, is a term I only learnt this week!

Thanks again.