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.
Connect a MOSFET to an Arduino directly
arduinomicrocontrollermosfetresistorstransistors
Related Solutions
First you'll need to find out / calculate / measure how much current the solenoid requires, and what voltage it requires. If the voltage is less than 50v (quite likely) and the current is less than 500mA, then you can drive it with a single outputof the good old ULN2803.
Here it is driving a bunch of solenoids. You can do up to 8. The best thing is that it already includes the flyback diode that you'll always need when you're switching inductive loads like this.
If you need more current, then you can use several outputs in parallel, up to a maximum of 2.5A.
The problem is being addressed with unnecessarily complex solutions. The crux of the issue is an incorrect assertion: "Since the voltage across the LED is only 2V, which is not enough for the Arduino to read, ...".
The Arduino's analog inputs are high impedance, and can happily read a 2 Volt signal. In fact, AnalogRead() would return a value of around 1024 x 2 / 5 = ~ 400 to 420 for an approximately 2 Volt signal.
So assuming the two circuits have their grounds interconnected, simply hook up the anodes of the LEDs to separate ADC pins of the Arduino, and use AnalogRead() on each. The high input impedance ensures that operation of the LEDs is not materially affected - even a voltage follower or a buffer is unnecessary.
Best Answer
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).
simulate this circuit – Schematic created using CircuitLab