Ok Disclaimer - Total noob to micro controllers, but i have some basic understanding of electronics theory so I’m not attacking something that is way over my head. And I have some basic programming knowledge from a while back, plus I’ve been looking for a project to get me back into it for a while now.
I am aiming to control 60-90 LEDs broken into 3 groups.
Group 1: 20-30x 1W (~3.2v @ 350mA) Cool White LEDs
Group 2: 20-30x 1W (~3.2v @ 350mA) Warm White LEDs
Group 3: 20-30x 3W (~3.6v @ 700mA) Blue LEDs
I have an Arduino Dumilanove that I borrowed from a friend to prototype with, and I’ve ordered 20 of each LED that I intend to use so I can do some testing.
My goal is to have dimming control from 0-100% for each group using PWM from the Arduino.
I have been looking at constant current drivers on ebay that support PWM (ie http://www.ebay.ca/itm/350539542188?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) and using a few of them in parallel, perhaps on a 36V power supply. But reading on here many people are suggesting using a CAT4101 chip for constant current driven PWM LED dimming? I looked at a spec sheet and it looks like it’ll work for me since it peaks at 1A, I’d have to break up the groups into a few strings in each since its < 25V (same as the drivers i’ve found online @ < 36V ). Also, it appears to be a SMD chip, and I’m looking to use through-hole components since i don’t really have the means to do SMD just yet.
The other option that I looked at, was using a large transistor to do the dimming - i used a 2n222a and a couple small LEDs to do some testing on a breadboard and it seems to work - any reason it wouldn’t scale to a high power led if i was to use a larger transistor (ie http://www.digikey.com - Part 497-7169-5-ND - I can’t figure out how to link directly to it, sorry.)?? I’ve done some current calculations and resistance calcs so I realize i’d have to break the groups up into strings and use some sort of 2W resistor or something to current limit, depending on my source voltage and string size… etc etc.
This is an aquarium lighting project, and i’ve searched and googled and i think i just need a push in one direction or the other as to which way to go - what do you all think? I’m going into mental melt down mode with the searching, i’ve got 3 windows open on my 24" lcd and i’m still scrolling left/right in the tabs lol.
The end goal is to use a RTC unit to control a sunrise/sunset/lunar kind of automated light cycle, and tie it all in with a temperature and PH monitor for the tank, all interfaced with a LCD and possibly keypad for programming/setting time/etc. maybe even get onto an Ethernet shield one day… but now I’m getting ahead of myself.
Oh Follow up Q - Can you set the PWM frequency on the arduino outputs? I saw someone talking about you could set it at 3khz or 16khz or something… or did i misunderstand something?