I am building a little pen plotter.

It is powered by a 12V 1.0A wall wart, as well as by a standard USB connection.

There is an Arduino Duemilanove, which will draw 120mA for the Atmega328 as well as 50mA for the control pins.

Attached to the control pins are three Easydrivers, that are supposed to draw 150mA apiece, and they are connected to stepper motors with 6 Ohm windings. these easydrivers are powered from VIN.

Also powered from VIN is a 12V 2.08W fan, which will run continuously.

Will this run without blowing something up?


If the drivers are good, they are constant current drivers so the coil resistance is irrelevant. The fan draws 2W/12V = 170 mA. So far that is 150*3 + 170 = 620 mA. If the Arduino draws another 170 on top of that, then you're looking at 790 mA. That leaves 210 mA of margin. So it will probably work, but I would check on exactly how much current the motors draw to make sure you're not going to get any large transients. The Arduino may end up drawing most of its current from USB, which would give you a bit more margin.

Edit: I suppose the Arduino will not draw any current from the USB connection. However, 170 mA is likely worst case and the actual draw will be significantly less. The I/O figure will probably be far less if you're just sending logic signals as those are not actualy sourcing any significant current.

  • \$\begingroup\$ No, the arduino will draw everything from the aux input. USB power is disabled if the aux jack is used. \$\endgroup\$
    – Passerby
    Oct 29 '13 at 5:08
  • 1
    \$\begingroup\$ The arduino does not need 120 mA to run. Maybe ~20 mA, but that's it. The 120 mA figure is only accurate if every IO line on the ATmega328P is being used to drive a load at it's maximum output current. \$\endgroup\$ Oct 29 '13 at 5:25

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