Is it safe to use the same power source for Arduino and its Motor shield?

Question

Is it safe to use a unique 12V 5A DC power source to feed both Arduino and its connected Motor shield, provided that

• the motor (connected to the shield) will eat 3A maximum
• the Arduino Vin will get the power

Arduino and the shield exchange information, and use both the same power supply, is there some risk of "interference" of some kind?

edit

This is the motor controller shield I intend to use. In the manual, the connections show that

• the Arduino and the shield have different power supplies
• the Arduino power pins are not used by the shield

• Len: Only if the motor gets it's power from the power source itself. If you power it through the shield and Arduino, you will still kill your Arduino.

Answer 1

In my case, when I was running my DC motors at full load, I noticed a large voltage drop in the circuit. This could affect the signals or transmission of data on the Arduino.

It is definitely recommended to power the arduino and motor shield with separate power source. Make sure the the share a common GND.

Answer 2

I'm assuming your shield has its own power input and you feed the circuit from there. If you are sure that your motor shield can hold that much current there shouldn't be any problem. You should see your motor shield's specs for that.

And actually if your shield has the standard arduino layout, it probably has an header goes into Vin pin. So even if you try to supply arduino from USB or power jack along with your power supply, the auto selector circuit of arduino board will use the power from 12 volt power source.

• Déjà vu: Please see my edit
• packt: Yea, it seems it's better to power the arduino seperately then like @goddar tells.