I'm using my Arduino Uno to control a 5V 1A solenoid.

I'm using an N-Channel MOSFET linked to the Uno's 0 pin to switch the solenoid on and off. It is protected by a Schottky diode. Initially, I tested the circuit with the blink example sketch (just set to blink Pin 0 instead of Pin 13). I used the Uno's built in 5V 500mA output and the solenoid "blinked" on/off perfectly at whatever interval I wanted:

5V 1A solenoid controlled by N-Channel MOSFET linked to Arduino Uno I/O pin, powered by Arduino Uno's built in 5V output

I plan on controlling multiple solenoids in a future version, which will draw more current than the Arduino output can supply, so I bought a 5V 12A power supply. I proceeded to test it with my single-solenoid set up using the same blink example sketch:

5V 1A solenoid controlled by N-Channel MOSFET linked to Arduino Uno I/O pin, powered by 5V 12A power supply

When I power the solenoid with my 5V 10A my power supply, the solenoid doesn't push on command. It merely "vibrates," travelling only about .5mm at several hundred Hz. The solenoid vibrates constantly the moment I plug in the power supply, and does so completely independently of whatever interval I have set it to "blink."

Any ideas as to what may be causing this to work with the Arduino's built in power supply, but not with an external power supply? I've tested the voltage on my power supply, and it reads 5V as advertised. I'm somewhat new this, and feel like I may be missing something obvious.




1 Answer 1


From your schematics it looks like:

  • you connected the power supply backwards (on both schematics actually, I wonder how come you did not fry your Arduino)
  • the external supply and the Arduino do not share a common ground as they should.

Edit: about the orientation of the power supply:

  • the (−) side of the supply (and GND of the Arduino) should be connected to the source of the N-MOSFET
  • the (+) side of the supply should be connected to the cathode of diode (the side identified by the small white bar)
  • Could you please elaborate on what you mean by the power supply being connected backwards?
    – MaxN
    Commented Oct 21, 2018 at 8:38

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