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[on:]

Hi everyone,

So I'm going to be making a dimmable LED moonlight system for my aquarium, and I have some questions about how to start it. So I don't plan on using the arduino to drive the LEDs, but rather control them. My problem is how to go about doing this. I'm basically going to be using a wall wart to drive the LEDs, then have the arduino control the dimming using PWM with actual dimming based on a RTC module. How should I go about connecting the arduino to the wall wart so that the wall wart powers the LEDs, but the arduino controls it? On the programming side, it should be pretty easy to program a moon phase calendar type thing in, so that depending on the phase the LEDs are dimmed a corresponding amount. I'm sorry if this is a really simple/stupid question, but this is my first arduino project.

[Reply #1 on:]

If you are using a PWM signal to drive the LED's, you will need possibly a MOSFET system. If you get an NPN, You would connect the base of the MOSFET to the output pin of the arduino via a resistor(value unsure at this point but will vary with the choice of mosfet) the collector to GND and the emitter to the anode of the LED(s). you also need to link the GND of the Arduino to the GND of the plugpack. Can anyone verify my logic here? Also I think you would benefit from a voltage regulator too.

[Reply #2 on:]

If you are using a PWM signal to drive the LED's, you will need possibly a MOSFET system. If you get an NPN, You would connect the base of the MOSFET to the output pin of the arduino via a resistor(value unsure at this point but will vary with the choice of mosfet) the collector to GND and the emitter to the anode of the LED(s). you also need to link the GND of the Arduino to the GND of the plugpack. Can anyone verify my logic here? Also I think you would benefit from a voltage regulator too.

MOSFETs don't have base, emitter, and collector leads. They have gate/source/drain leads. If you use a mosfet be sure it's a logic level mosfet. The connections told above are for a NPN bipolar transistor. A TIP120 is a nice cheap darlington NPN transistor that is great for switching things on or off or PWM from an Arduino output pin.

Lefty

[Reply #3 on:]

Sounds pretty good, but the pin connections you describe are for a BJT transistor, not a MOSFET.

[Reply #4 on:]

Ok so lemme see if I have this right:

I can use either a MOSFET or NPN transistor. The MOSFET needs to be a logic level one. If I use an NPN, it can basically be any kind that fits the power needs (current, voltage) of the LED string?

[Reply #5 on:]

Alright thanks for all the help guys