Question on LED driver from PWM output circuit

[kcress]

Originally Posted by snorkeler

OK, found the answer.... here: http://www.reefcentral.com/forums/sh....php?t=1751598

I should subtract LED voltage drops from power source, so my R would be 0R7. Also interesting to add a 1A fuse to the circuit.

Thanks kcress for that thread!

Yes you got it. Thanks, by the way. You sub out the LED drops.

Don't forget the resistor's power rating either.

Do V x V / R = Power for the expected power being dumped on the resistor.

Then double the number and find the next larger power rating. So if the power came out at 2.2W => 4.4W => use a 5W or larger.

[xrunner1234]

For gate resistor just use a 10ohm resistor.
The charge time will mostly be defined by port current and as far as a pull down does the port go "low"? If it does then you'll have a hard pull-down.

Don't worry about audible noise switch at low frequencies. I'm sure that there is no mechanical movement from a couple of LEDs and resistors.

[snorkeler]

I finally built the first prototype, and it is working, dimming from the Arduino's PWM output, MOSFET, LEDs and resistors not heating up, using a PC ATX power source, realy cool!!!

I'm very happy over here, thanks a million for all the pointers kcress!

Now I just need to get some time to do the whole build. But that's going to be easy, just drilling, soldering and fixing.

Here are some pictures:

ATX power source, Arduino, MOSFET driver, fuse, and 3 LED lamp.


The Arduino and MOSFET + Resistor driver circuit:


Arduino, MOSFET driver, fuse bar and 3 LED lamp:


I shot a video of the dimming with my cell, but it's taking rather long to convert and show up in YouTube so I'll skip that for now and post it once I see it appear.

Snorkeler

[kcress]

AH man.. Nice. Kudos.

LEDs are great. They reward successful DIYers with scads of obvious light.

Any noise?

[snorkeler]

Nope, no noise at all. It was late at night, house silent, I'm pretty sure no noise. In fact, the only thing I could hear was the ATX power source's fan :-) .

Got the video up, finally. Very quick/short, just shows the dimming then a closeup in the MOSFET circuit, to show how small/simple it is:
http://www.youtube.com/watch?v=8JQBkOU6K5Q

Snorkeler

[snorkeler]

It has been a while since I last posted here, mostly because progress has been in slow steps, spaced apart. Today I completed a major milestone, finished the whole controller box! In other words, what was just one prototype in my Jan 11th post is now a complete box with the capacity to control 10 "3-LED lamps", wired to the Arduino, with connectors, etc.

Pictures here:

Controller with the eight "3-LED lamps" I built (might not need ten, but have the capacity for ten):


All lights on:


Closeup of the controller and Arduino box:


I was very happy when I powered everything up and it worked, with the Arduino dimming them up and down.

I left if 100% on for quite a while, and no wires nor components seemed to heat up, so I guess everything will resist day to day use well, including the PC ATC power source which at 100% is supplying 8A.

Next steps now are redo my aquarium hood (draw and ask a local woodworking company I trust to build it) and fix the aluminum frame that will hold the "3-LED lamps" (fix = elevate the lights to distance them from water, using optics to focus the light... my first frame build was too low and won't work well).

Probably another 2 months until all that is finished...