First go with an Arduino


Hi to the forum. I am taking a first try with an Arduino board by building a motorized telescope focusing unit from a project on SourceForge. This project uses an Arduino Uno with an L293D motor shield. The stepper is a 28BYJ-48 motor rated at 5-7.5v. Setting this up and burning a test program to the Arduino results in a fully functioning motor powered by the 5V USB connection to the laptop. The focuser unit will be operated through a Windows program so the USB port will be connected all the time. Running the motor in this configuration is convenient. However the Arduino board offers an external power jack, and the L293D has facility for a separate power connection. Should I wish to use a 12 volt stepper motor, I would have to provide this voltage through either external power connection.

My question is whether the provision of 12v through either the Arduino or motor shield external power jacks will conflict with the 5v USB power that is now running the motor? The L293D has a jumper that allows power to the motor shield to power the Arduino board. Is this a good idea if the USB port is in use? Is it better to power the Arduino Board with 12V, or the motor shield?

Appreciate some help with these basic question. I look forward to focusing my telescope from the desk instead of standing outside in winter.


Typically, it is recommended to use a separate power supply than to branch off the same power supply. The Arduino chip can’t source enough power for both the driver supply and controlling the motor. Most motor driver shields have an external power input. A motor driver sinks a lot more current, but controlling the driver barely uses anything. However, if you had a 12 V power supply capable of sourcing the power for the Arduino AND the motor driver, you could power both in one shot. So the power supply can do both, but the Arduino itself cannot do both.


Would powering both the Arduino and motor shield produce and conflict if the USB port was in use on the Arduino?


No, I have done this before. The 5V supply is isolated so no problems occur when powering the driver at the same time.


Ok thanks. I will try this with the motor I am now using by supplying 7.5v to the motor shield and leaving the jumper in place that allows power to the Arduino board. I will be using the USB port on the Arduino board at the same time.