Below is a circuit of my suggested setup.
Connection of the plug pack GND to the Arduino GND is necessary as a reference level for D13 to the Gate. Otherwise the voltage would be floating and the triggering may or may not occur.
The data sheet for the mosfet shows it approaching saturation at 5V on the Gate, resistance 0.032 ohms. So it should operate nicely as a switch.
The 120 ohm resistor is for testing and reduces the current to a non dangerous level. Use the formulae below to calculate a resistor value for higher brightness levels.
ie Current = 0.5A, LED wattage = 6.5 * 0.5 = 3.35W.
Resistor = 5.5 / 0.5 = 11 ohms. Watts = 5.5 * 0.5 = 2.75W. Use a 10ohm, 5W resistor.
Disclaimer: I have not built the circuit.
Ensure you understand what you are doing before switching it on.
Test the LED by connecting just it and the resistor to the plug pack. (I think you have already done this)
Test the mosfet switching of the LED before connecting the Arduino.
Test the Arduino control of the mosfet by writing a high to D13 then a low. The on board LED should turn on as well.
Anyway, all the best
Jim
2 Likes
Good James
That is exactly what I have been trying to describe. The only criticism I have is the choice of 120Ω resistor. This LED is quite a high current device and 120Ω will only allow 46mA. This may not light the LED and may confuse the issue if Kooper thinks he is doing something wrong when the LED does not light. Of course it might glow in which all is OK.
Kooper.
This circuit is exactly how this should be wired.
If the LED does not light it may be that the 120Ω resistor is a bit high. If this occurs reduce the value. You should be able to get down to about 56Ω without risk of any damage or over bright LED. This equates to a current of about 100mA. at this point a 1W resistor should be OK. Up to 5W would not hurt.
Cheers Bob
2 Likes
Agree Bob, the datasheet lists 6.5V forward at 400mA; without some testing I have no idea what it would be at 46mA. If the LED on the UNO lights and the Super Bright LED does not then the resistor is at fault and should be reduced. Calculation of the watts for the resistor would be most important. If anything, Kooper should buy a few different values rated at 5W.
cheers
Jim
2 Likes
Hi James
A LED is essentially still a diode. Like most diodes the forward voltage drop once turned on will not change much over a wide current range. An equilibrium will be established where the current may not be exactly 46mA and the voltage drop will not be exactly 6.5V but it will not be too far away.
Cheers Bob
PS: I have often seen LEDs double up as an indicator and cheap and cheerful voltage reference where the actual voltage is not critical but does not change over some current range.
1 Like
