Fading a 60W bulb (or equivalent)

[john444]

Hi Matthew1,
Just for grins, try connecting a resistor from the FET's gate to source.
Should be the two outside pins.
Can be anything from 1-Meg to 1-K. See if the FET turns off.
You have mentioned several FETs. Which are you using?

[Abrahamkite]

It doesn't have to be a 60W bulb, 40W is just OK,I think.

[matthew1]

I am using the mosfet from the store https://www.adafruit.com/products/355 and also trying a TIP120

the mosfet is slightly working and the tip120 is working at all.

Also, I am currently using a 15watt bulb at 12v, not 60w

[matthew1]

John I added the resistor but no change. The fet is working but the gate voltage still wont drop to zero. On the TIP120 the gate is still latching.

[john444]

Matthew1,
I am going to take some guesses here, since you say the FET is working and I don't know how you have been testing.
Consider these possibilities: they are pretty easy to check.
Poor connection or high resistance to the FET’s gate – bypass any series resistance or connections
The lamp’s turn-on current-surge is upsetting the Arduino – power the Arduino from a 9v batt
The Arduino’s output pin is damaged in a way that it stays high – change the code to use a different output pin.
Good luck

[matthew1]

The mosfet was tested using a multimeter while the arduino sent high and low signals to the gate. I have also been running the arduino from a 9v battery and tried several different codes and arduino pins.

With the mosfet, I have be able to get the bulb to blink slightly but never completely off.

With the TIP120, no activity, just on (latching)

[john444]

It is not clear to me:

The fet is working but the gate voltage still wont drop to zero.

When the Arduino pin is low and you put a V meter from gate to source - the voltage does not go to 0?
Or, the meter does not seem to indicate 0 when the gate is being pulsed for the fading effect?

[adafruit_support_bill]

Has the Arduino pin-mode been set to OUTPUT?