Hello everyone.
I have in project the use of a stepper motor with Arduino Uno . I wonder if there is a way to use a 19v laptop power supply to power the stepper motor and the Arduino to avoid having two power supplies.
For example using an adjustable step-down module to power the Arduino with 9V ? Is it safe to do it or is there a better way ?
Something like that:
Thnak you 
I think that concept should work OK. Put a big capacitor on the input to the motor driver board so short term demands for current don't interfere with the Arduino.
You seem to have connections from the Arduino GND and VIN to the high voltage. That will let the smoke out very quickly.
You don't need a connection between Arduino GND and stepper power supply GND.
A photo of a pencil drawing of a wiring diagram is a more reliable guide than the sort of image you posted.
...R
Thank you robin. To be truth that's a picture i found on google image. I just added the power supply and the down step module to show what i was talking about.
Seem's Pololu recommand at least 47uF capacitor. Is that ok ?
overcool:
To be truth that's a picture i found on google image. I just added the power supply and the down step module to show what i was talking about.
That is a very risky way to do things because you don't know what they have really done and neither do I. I think I should WITHDRAW all my comments until you post a photo of a drawing of how you plan to connect things.
Seem's Pololu recommand at least 47uF capacitor. Is that ok ?
This is outside my comfort zone. If you look at some of the Posts in this Thread you will see recommendations for capacitors of some thousands of micro farads. I leave you to make your own decision.
...R
Well sorry, as i said it was just to show what i wanted to say. I am French and sometimes it's a little hard to find the words to express myself properly in English so i thought a picture would be helpfull. I was not going to use the Vin but i understand your concern.
Thank you for your help.
Fritzing diagrams are confusing, difficult to interpret, often misleading and should be avoided.
They are appropriate only for complete beginners, and only for the very simplest of projects.
If you are at all interested in electronics, it is far better to learn how to use standard schematic diagrams.
overcool:
Well sorry, as i said it was just to show what i wanted to say.
No apology required or expected. I was just concerned that you might ruin your Arduino without thinking about it.
...R