Fading a 60W bulb (or equivalent)

[matthew1]

I think is is what I am looking for, the circuit is simple using only a TIP120 Darlington Transistor and a resistor and can handle the 12v DC lamp

[adafruit_support_bill]

A TIP120 should work. The MOSFET is a bit more efficient.

[matthew1]

Great, I will go with the MOSFET then. Thank you all for the quick responses. I will post photos/videos when this gets rolling.

[matthew1]

I have my mosfet wired like the diagram above and I am using arduinos example sketch blink to control the gate... But... nothing? The bulb works fine and I am baffled as to whats happening. Could it be code? or should I wire it differently than the above diagram?

[matthew1]

Also, I am using a 12vDC supply at 1.5A

My bulb is a 12vDC 15watt

Here is the link to the mosfet:
http://www.sparkfun.com/products/10256

and the arduino is running the blink example on pin 9

[matthew1]

Is it possible I need a different mosfet or transistor?

[adafruit_support_bill]

I have my mosfet wired like the diagram above

The diagram above is for a TIP120, not a MOSFET. The data sheet for your device most likely has diagram of a typical circuit.
The MOSFETS in the store here can be driven directly by a digital pin - no resistor required.

[matthew1]

I will give those a try!

[matthew1]

MOSFETs came in today, wired them and tested the circuit with the blink sketch. It works but barely, the bulb remains at it's brightest and then when it's supposed to turn off it just becomes slightly dimmer. When trying a fading code there is almost no change and the bulb appears to remain at full power.

Very new to working with these, any reason why I can't get a full range of brightness from the bulb?

[philba]

Clearly, the mosfet isn't turning off. Post the circuit. What is the gate voltage when it's supposed to be off? (should be 0). How are you controlling the gate? (i.e. show us the sketch).

[matthew1]

Code: Select all

void setup() {               
 
  pinMode(9, OUTPUT);     
}

void loop() {
  digitalWrite(9, HIGH);   
  delay(1000);           
  digitalWrite(9, LOW);   
  delay(1000);             
}

The code is just a simple blink sketch, same as the one that is in the examples on the software. The MOSFET is wired to pin 9 at the gate

[matthew1]

Still getting the same results with different code

[philba]

It's not the code, show us the circuit.

[matthew1]

From the DC converter, the positive lead goes through the bulb and connects to the orange wire in the photo

The negative lead connects to the grey wire and then the green wire connects to arduinos ground

Finally the yellow wire connects to arduino's pin 9

[matthew1]

I've taken the circuit to my school's arduino/robotics teacher. He confirmed everything is wired properly and we even the tried the TIP120 circuit. We found that the gate works fine without the DC converter plugged in but when we do plug it in, the gate stays high. He was at a loss for why this was happening but said it was a "latching" issue.

Has anyone else had this problem or know how to get around it?