Thought I would share my DIY LED setup on the forum here.
This has been a slow project for me but has been steadily progressing. I have always wanted a dim-able LED setup so I could simulate the Dawn and Dusk periods of a "Natural" day. This way the fish can adjust to the increasing light unlike an ON/OFF timer. About a month ago I decided to bite the bullet and dove in.
In a nutshell, I have created an LED fixture and a timer that displays the current time and the current brightness as a percent of full bright on an LCD screen. I am using a Rotary Encoder, like the volume knob on your stereo, to manually control the brightness level of the LEDs as well as set the time and program transition intervals.
For power, I am using a PC ATX PS (power supply). Its rated at 12A on the 12v rail and more than I will even need on the 5v and 3.3v rail. PC power supplies can be found on the cheap too. I went this route because I am creating my own light timer that will dim or brighten the LEDs at programmed intervals and the hardware for that requires 5V.
For the LEDs, I found some 10 watt ebay LEDs that are perfect for my needs. Search ebay for "12V 10W 600Lumen White Led Energy Saving Lamp NEW" to see them. $7 each and they are rated for 12V at 1A, I am feeding them around 900mA and they are plenty bright. I am also very pleased with the color, somewhere around 7000K, much whiter then standard T8 6500K. They are not the best LED you can get, but the price is right and they are super easy to mount.
For the fixture, I needed something that would allow for easy tank maintenance and act as a heat sink for the LEDs, at 10 watts each they get hot. I went to Lowes and bought some L and U-Channel aluminum and made the following. I kept the fixture to two separate pieces so I could have full access to one side of the tank while still having good light over the other side. I used banana plugs and jacks for easy disconnects when I want to move stuff around
Pardon the messy tank. I am waiting to move so the tank has been in limbo for a while now. Just been working on getting all the hardware I need together.
Anyways, to keep the LEDs running at 900mA from the 12V PS, I put a 2.2Ohm 10Watt wirewound resister in series with each LED. Each LED is wired in parallel with the 12V PS, this way if one LED ever buns out the others will still work and not get overloaded.
My plan is to use 8 of them for OK coverage while still maintaining the shimmer effect. So far I only have two hooked up for testing and I am happy with the results. 8 of them will be BRIGHT (theoretically 80 Watts)!! Good enough for a low light setup on my 90 Gallon if not better. I can say that the two LEDs are about as bright as one 2xOD 48" T8 with an icecap T5 reflector.
For the timer, I am using an ATMega16 Micro Controller. It needs a 5v input and using the power supply 5v output eliminates the need for 5V voltage regulator. I am also using the 3.3v rail for the LCD back light. The ATMega16 controls a MOSFET via PWM (pulse width modulation) to dim or brighten the LEDs. The LEDs get their power from the MOSFET.
The timer is like those digital ON/OFF light timers you can find at Wal-Mart or wherever but it also allows me to set a "light level" and a "Transition Length". The "light level" is a percent of full bright (0.01% to 100%), and the "Transition Length" is the time span in minutes (1 to 30) over which the brightness will be adjusted. The timer can also act as a ON/OFF switch if I choose.
Here is an example of how it works.
Say its 5PM and I have a current light level of 75% of full bright.
At 5:30PM the timer will dim the LEDs to 10% over a 30 minute time span (Simulates Dusk).
At 10:30PM I can dim the LEDs to 0.05% over 5 minutes (good moonlight level).
At 10AM the next day I can brighten the LEDs to 75% over a 30 minute time span (simulates Dawn).
At 12PM I can brighten the LEDs to 100% over 10 minutes for a noon burst then dim them back to 75% at 2PM.
At 5:30PM it will dim back to 10% over a 30 minute time span (Simulates Dusk).
I can also manually adjust the brightness at anytime by tuning the Rotary Encoder clock-wise or counter clock-wise to brighten or dim the LEDs.
I uploaded a crappy video of the LEDs transitioning from off to 100% over two minutes.
I still have a lot of work to do like adding 6 more LEDs to the fixtures (4 per fixture) and I need to finish writing the code for the Micro Controller but Im happy with were this project is at so far. When I get some more LEDs mounted I will upload another video.