I am building a robotic arm for Science Olympiad at my high school and I really want to have an electromagnet on the end of the arm to pick up nails. I planned to program the Arduino to respond to the push of a momentary switch. This would tell the Arduino to send a HIGH signal to the gate of a MOSFET which would then allow the electromagnet to power itself from a different, stronger, power source, rather than the Arduino.
My problem is with the MOSFET transistor. It is NPN (I'm pretty sure...) and I have looked up the data sheet (http://pdf1.alldatasheet.com/datasheet-pdf/view/52980/FAIRCHILD/IRF630A.html) to be sure of the pinout. No matter what I try, I cannot get the supposed gate pin to effect the state of an LED (I am using this to make sure I have connected the MOSFET correctly). The LED stays HIGH. I have even tried reversing the transistor in case the data sheet or my understanding of it was incorrect. I cannot figure out what to do. I will attach several pictures including what I believe I have hooked up in a schematic, as well as two shots of the setup. please bear with me in the way that I know I only have one power source in use here. The original was in a crowded breadboard, so I quickly mocked up everything on a clear(ish) one to make it easier to see. In reality, I want the Source and Drain pins to be connected to a 7.4 volt Lipo battery.
And yes I know the pictures show nothing hooked up to the third pin. That would be connected to the positive of the battery.
I spent quite a time trying to get this to work. I am so frustrated right now that anything you can tell me would be much appreciated.
I couldn't get my photos to work right so here are the links to them. http://www.flickr.com/photos/brandondub/8428913456/in/photostream http://www.flickr.com/photos/brandondub/8427821511/in/photostream http://www.flickr.com/photos/brandondub/8427822445/in/photostream