How to power motor shield

Hee folks,

I have completed the Arduino Started kit recently and I'm now building a project for my own, which includes the following:

Now my problem is the following: for prototyping I want to connect the arduino uno to my computer via the USB cable. I want to power the motor shield with a second power supply. Now here comes my problem: I prefer to buy a wall adapter AC-DC 12 Volt, 2A (and I will adjust the voltage giving to the motor with the stepper driver, DRV8825). But all adapters have a DC Jack, but I need to connect two seperate wires to the motor shield. This might be a really stupid question, but do I have to cut off the jack and try to seperate the wires and then connect these to the motor shield? Isn't there a better solution for this?
I have been googling a lot to find solutions how to power up or wire/connect a power supply to a motor shield, but couldn't find the right answer.

Secondly, is there a way to power up the Arduino and the CNC motor shield with only one power supply with this configuration? That the CNC Shield gives 5V DC to the Arduino?

I hope someone could help me out, thanks a lot in advance

You could buy a socket to match the wall wart plug and wire that to the CNC shield, but I would just cut the plug off.

The CNC shield does not supply 5V to the Uno. You could get a 12V to 5V DC DC converter.

Thanks groundFungus for your quick reply. I will buy an adapter then and just cut it off and connect the wires to the shield. Should check polarity first ofcourse.
Is this the best way you think? Or would you recommend to buy something else/to power up the Shield in a different way?

As long as the 12V supply has plenty of current capability it should work fine. And, absolutely, insure correct polarity.

Make sure to adjust the stepper coil current limit on each stepper driver This Pololu page has instructions.

Think twice about powering the Arduino through the Vin or the power jack. Powering through Vin or the power jack means that the Arduino and all peripherals that are on the 5V rail are powered by the onboard 5V regulator. The on board 5V regulator is not heat sinked so will supply limited current before it overheats and shuts down. The recommend max power dissipation for the regulator is 1 Watt. With 12V into the regulator the max current is about 140 mA (1W / (12V - 5V)). The Arduino uses around 50ma of that leaving less than 90mA (max) for everything else.

I would use a buck converter to drop the 12V to 5V and connect that to the 5V on the Arduino, bypassing the, weak, 5V regulator.

Once again, thanks groundFungus.
Correct me if I’m wrong, but for my first testing case I will be using the adapter AC-DC 12V/2A To the motor shield and regulate the current limit with the stepper driver and it’s Vref for the motor.
The arduino in this case will be powered by a separate power supply (usb to computer).

After finishing my test results, I will try to make a first fully functioning prototype with 1 power supply by connecting the motor shield to the adapter. A DC-DC step down convertor, 12V to 5V, will be needed as well, to power the arduino from the motor shield and connect that to the arduino uno.

Is that correct, or do I miss out on something?

Yes that is correct. Connect the output of the 12V to 5V DC DC converter to the 5V pin of the Arduino, not the power jack or Vin. There are a couple of places on the CNC shield to connect 5V and ground from the DC DC converter. Look in the black boxes.

Available at numerous other sources.

GroundFundus, thanks!
So I have to split the output wire from the DC adapter into two wires, one connecting to the power supply of the cnc shield and one connecting to the buck concertor, which then can be connected to one of the 5 Volt pins on the CNC shield which needs to be connected to 5V pin of the arduino, or I can simply just plug the wire from the buck converter into the 5 volt plug of the arduino straight away..?

Furthermore, now I’m using a CNC Shield with one DRV8825 to control one steppermotor. I have bought the CNC shield and the DRV8825 because they are so cheap, but it gives me the feeling that a CNC shield, meant for controlling 4 motors, is a bit overkill and that there is a more simple configuration to do this?! I saw some motor shields to control one stepper motor, but they didn’t have the right voltage requirements for my motor... what is your view on this?

Thanks also JCA34F, that is nice one indeed.

can simply just plug the wire from the buck converter into the 5 volt plug of the arduino straight away..?

With the CNC shield in place there is no 5V or ground accessable on the Uno itself. Connecting to the 5V and grounds on the CNC shield (black boxes) will supply power to the Uno.

Do not power the Uno through the 5V pin (external 5V supply) and USB at the same time.

I like the CNC shield because it simplifies connection of multiple motors, limit switches, etc. The downside is that the pins on the Uno are less accessable. For just one motor I would probably do the wiring on proto board (soldered).

Alright! Thank you so much for all your help. I will try it first with the CNC shield (after all I already have it now and it is so easy to use) later on I will try to solder my own proto boards. Only disadvantage then is that I have to go back to the separate power supply set up again.