I've read around about this topic.
Here's my question: I'm running a project with 2 stepper motors both of which require 12v. The Arduino (mega) takes 12v input in the barrel jack.
Instead of adding another 12v power supply, why can't I just power the motors either by using the vin pin on the arduino, or just soldering cocnnections to the 12v barrel pin mount on the arduino? I read that the Arduino doesn't care how much amperage there is in the power supply, so why can't I just use a more powerful 12v adapter to power both the Arduino and the motors?
Am I missing something here? thx in advance...
Who said that you can't?
I'm not much of an electronics engineer but I think that the only thing to be aware of is that peek current by the servos might introduce drops in the 12V voltage. A fat electrolytic capacitor over the 12V that goes to the Mega should solve that.
Also be aware that you can not draw much current from the Mega's 5V pin when powering it with 12V.
There's a diode between the barrel connector and the Vin pin. The M7 diode is rated for 1A. As long as your steppers don't take more than that (minus whatever the Mega needs), it'll be okay. Remember that it will have ~1V drop across it.
That would remove the diode from the equation and the 1A limitation would vanish. Also you'd get the full power supply voltage to your steppers.
Or split the power supply cable. More elegant way would be this:
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The problem you face is if you power the motors from the Arduino you will probably fry (damage) it. This includes ground current as well. @kmin has a good solution with the splitter cable, both the motor and arduino go to the same power supply which can supply enough current for everything. None of the current the motor requires passes through the Arduino (good thing). I do this all the time.
There is got-ya in that some of the Nanos do not have the 5V isolation circuit. If this is the case the output of the Nano's 5V regulator can feed back into your PC. There have been occasions where the 12V was connected to the 5V on the Arduino frying the laptop.
You can make a pseudo isolation USB cable by cutting the red (on the ones I have) to isolate the 5V.
I could of course run 120 to the project box and just include a 12v converter and run both motors and the arduino off of that. takes up more space, is all. But a perfectly viable solution. I was just musing on doing it in the minimum space possible.
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I ended up just buying the smallest 12v power supply I could find and putting it in the box. Separate wires to the mega and to the 2209 12v motor power pins. So 110v to the box, can be set up anywhere.
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