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I need a simple diagram showing me how to switch 12V LEDs with a 2N7000 using an Arduino. My experience is moderate, but a simple diagram should get me started. To summarize I want to switch 12V with 3V using 2N7000 MOSFET, a LED strip, and an Arduino Uno. Also when I hook up the 12V LED strip's ground through the D and S of the 2N7000, it ligths up without anything connected to the Gate. That means it is open until it recieves what signal on the Gate?
I've tried this:
Using a 2N7000 is, as a first approximation, just like using a BJT to switch a load. The major differences are:
the gate is (very) high impedance, so no resistor is required to limit the current, as a resistor would be needed in series with the base of a BJT
the gate threshold of MOSFETS is typically higher than the 0.6V it takes to get a BJT to turn on
The datasheet will specify a gate threshold voltage \$V_{GS(th)}\$, which is the voltage at which the transistor begins to turn on. You want to apply more than this if you intend to operate the transistor as a switch. You also want to apply safely less than the specified absolute maximum gate-source voltage, which if exceeded, will destroy the device. I happen to know off the top of my head that 5V is a good gate voltage for 2N7000, which is convienent because you can connect it directly to your Arduino.
What you are missing, it seems, is how to use a transistor as a switch. Searching for "transistor switch" turns up a few million tutorials, but here's the brief version:
Applying 0V to the input makes the transistors appear like an open switch, and your load (represented by resistors) is effectively disconnected from the power supply. Applying a higher voltage (whatever voltage is used for the logic in your circuit, usually 5V in the case of Arduino) turns the transistors on, and they look like a closed switch, effectively connecting your load between Vcc and ground.
