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I have the following electromagnet and plan on connecting it to the following MOSFET which will be controlled by an Arduino (I'm thinking analogue or PWM). Do I need any other parts (resistors etc.) I'm sorry about the vague question but I don't know much about electronics at all and am just starting. By the way, the aim is to be able to control the strength of the electromagnet (12v 300mA-1A) using the Arduino easily.

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  • \$\begingroup\$ You can connect the gate to the MCU output with a current-limiting resistor. Also make sure you have a common ground. But a fail-safe (to some extent) solution would be to use optical isolation. \$\endgroup\$ – Eugene Sh. Aug 26 '15 at 17:49
  • \$\begingroup\$ @EugeneSh. What is the MCU output and what is optical isolation? sorry but as I mentioned in my question I have just started working on electronics \$\endgroup\$ – DividedByZero Aug 26 '15 at 17:50
  • \$\begingroup\$ So probably you should familiarize yourself with the terms first. \$\endgroup\$ – Eugene Sh. Aug 26 '15 at 17:51
  • \$\begingroup\$ @EugeneSh. Well I know what optical isolation is but I don't know how that would be used in this case.. And as far as MCU output is concerned, I am learning on my own and can't find anything on the internet related \$\endgroup\$ – DividedByZero Aug 26 '15 at 17:53
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You can connect a MOSFET directly, even without a resistor if you like (though it's not nice to put such a heavy load on the output), but if the MOSFET fails with a Drain-Gate short your Arduino will be scrap. I strongly suggest using a higher voltage MOSFET than that one- it's only 12V and you will at least be subjecting it to at least 12.5-13V when the MOSFET turns off. It does have nice specs at 4.5V drive (good for an ampere or two), but Vds breakdown is too low.

If you want a modicum of protection, (Edit: Assuming 5V Arduino) put a 5.1V zener on the Arduino output and a 200 ohm metal film resistor to the gate. Put 10K across the 5.1V zener as well so if the output goes open it won't partly turn on.

You must put a catch diode across the coil. Something like a 1N5819 would be good. Otherwise the MOSFET will get very hot and may fail very quickly.

Edit: You should make sure the MOSFET you select is capable of handling the full current of the solenoid (1A you say).

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Do these values apply to both the 5V and 3V3 versions? (BTW - the OP does state the current range for the 12V solenoid as 300mA to 1A) \$\endgroup\$ – JIm Dearden Aug 26 '15 at 18:14
  • \$\begingroup\$ If I use a higher voltage MOSFET will my Arduino still face the threat of a drain-gate short? \$\endgroup\$ – DividedByZero Aug 26 '15 at 18:15
  • \$\begingroup\$ @RandomUser Yes, it's an inherent risk with non-isolated circuits with mixed voltages. That's why Eugene suggested opto-isolation. \$\endgroup\$ – Spehro Pefhany Aug 26 '15 at 18:16
  • \$\begingroup\$ @JImDearden Okay, edited, thanks. It applies for the 5V version. The knee is too soft on 3.3V zeners to be assured of protection. Maybe use a blue LED capable of 100mA rather than the zener. \$\endgroup\$ – Spehro Pefhany Aug 26 '15 at 18:18
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    \$\begingroup\$ looks good to me +1` \$\endgroup\$ – JIm Dearden Aug 26 '15 at 18:41

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