I am new to electronics. I have a MOSFET that I'm gonna use to activate a solenoid, but for now I wanted to test it with a resistor. This is my design.


simulate this circuit – Schematic created using CircuitLab

When I hook up a power supply to the gate and source, it turns the MOSFET on and off as expected, causing the meter to read 5V when on and 0V when off. The problem is when I try to have an Arduino Uno take the place of the V_gs power supply. I first connect the circuit ground to the GND pin. Then I connect the gate to the 5V pin. It turns on normally. The problem is when I connect the gate to one of the other GND pins on the Arduino, it stays on. The only way I can turn it off is by physically touching the gate and source wires together. How is that possible? I thought all of the GND pins were internally connected. What should I do to fix this?

I'm using an FQP30N06 MOSFET.


  • \$\begingroup\$ Does your Arduino share ground with MOSFET drain? \$\endgroup\$
    – winny
    Commented Nov 18, 2023 at 16:49

1 Answer 1


It sounds like the GND pin you think you are connecting to is actually floating for some reason or another (bad jumper wire, bad solderless breadboard connection, bad solder joint, wrong pin selected, wrong markings, something like that).

Also the FQP30N06 is inappropriate for 5V drive, it's specified with 10V drive. It will work with a relatively high value resistor, but may be marginal, overheat or whatever with a high current solenoid. The solution is to pick a better MOSFET (logic level drive) specified at 4.5V or less Vgs.

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