user639: On an Arduino Uno, the PWM pin 3 is connected to the gate pin of an N-channel MOSFET STP16NF06L. The source pin is connected to ground of a 12 V power supply and drain pin connected to a multimeter. The other end of the multimeter is connected to the positive terminal of the power supply.
Question: When Arduino varies its PWM output from 0 to 255, the multimeter reading goes from 11.50 V to 12.10 V. Why isn't it 0 to 12 V?
When the FET gate is connected to the Arduino pin that outputs either 0 V or 5 V, the multimeter reading is as expected at 0 V and 12 V respectively.

user3879: Assuming you have a suitable FET You should have a circuit in line the following.
http://elinux.org/RPi_GPIO_Interface_Circuits#Using_a_FET
You should have some kind of load (a multimeter will have too high an impedance). Use a resistor 4.7k or smaller. You should also have a resistor on the gate

639: <p>On an Arduino Uno, the PWM pin 3 is connected to the <code>gate</code> pin of an <a href="http://www.farnell.com/datasheets/1690175.pdf" rel="nofollow noreferrer">N-channel MOSFET STP16NF06L</a>. The source pin is connected to ground of a 12 V power supply and drain pin connected to a multimeter. The other end of the multimeter is connected to the positive terminal of the power supply.</p>

<p><strong>Question:</strong> When Arduino varies its PWM output from 0 to 255, the multimeter reading goes from 11.50 V to 12.10 V. Why isn't it 0 to 12 V?</p>

<p>When the FET gate is connected to the Arduino pin that outputs either 0 V or 5 V, the multimeter reading is as expected at 0 V and 12 V respectively.</p>
 3879: <p>Assuming you have a suitable FET You should have a circuit in line the following.
<a href="http://elinux.org/RPi_GPIO_Interface_Circuits#Using_a_FET" rel="nofollow">http://elinux.org/RPi_GPIO_Interface_Circuits#Using_a_FET</a></p>

<p>You should have some kind of load (a multimeter will have too high an impedance). Use a resistor 4.7k or smaller. You should also have a resistor on the gate</p>
