Well, since there is no power to the Arduino Nano, I guess it needs an additional power supply. Or connect it to the USB along with the two other chips.Your PC USB will shut down if too much current is drawn from it. You will have to turn the PC off/on to recover.Paul
Looking at the schematic it looks like the USB port is just there to supply power not a signal. The PC will be connected to the Micro USB on the Arduino and used to send the data for the image that is being drawn? So maybe could I ommit the USB and supply the L293Ds with a power from a battery pack or regulated 5v?The Nano will be powered by the PC via the Micro USB Port? Or should I tap of 5v regulated for the Nano also?
If you are going to use the USB serial connection to the Arduino, just let it power the Arduino and use a separate supply for the stepper motor control. Be sure to connect all grounds together. Paul