The Aquatic Gazette

jcardona1′s Wild Discus Biotope (2)

In Build on May 2, 2011 at 21:26

Welcome to Edition 2! If you have missed out on Edition 1, it can be found here: http://theaquaticgazette.com/2011/04/28/jcardona1s-wild-discus-biotope-1/ Enjoy this edition!

jcardona1: Lighting is one that deserves it’s very own section, since I went into total crackhead mode here Click the image to open in full size. I did a lot of think and a lot of research before finally pulling the trigger. I know for certain that I did not want to run fluorescent lighting. I was tired of the “flat” look it gives the tank. It’s very unnatural, and I don’t like how every square inch of the tank is lit up evenly. I also knew I wanted the shimmer effect, so it was either metal halides or LED. Metal halides were completely out of the question, since I don’t like the idea of making the electric company rich! So, LEDs it was! I was almost set on running 4-6x 10w LED floodlamps you see more and more folks using these days. In the end, I decided to go DIY to give me more flexibility. These floodlamps are made in China, so you can’t really know how long they’ll last, or whether you’ll be able to buy replacements in the future. But the main reason for going DIY was color choice. ‘Cool white’ LEDs are ugly in my opinion. They wash out the color of fish too much. The warm whites are very yellow. If I chose the floodlamps, I wouldn’t be able to mix up the colors to get a nice mixture.

The light bar itself I made out of 1” metal conduit, which I bent into shape using a manual pipe bender. The light fixture is a big and heavy piece of aluminum heatsink, measuring 7×36”. I also attached a splash shield made from ¼” acrylic. The shield really isn’t needed, but it finishes off the fixture nicely, makes it look more legit.

The LEDs are Cree XP-Gs. They cost a little more than other brands, but the quality and reputation is well worth the extra cost. The fixture uses 12 neutral white LEDs (4000k) and 12 warm white LEDs (3000k). They are arranged in two rows of 12, alternating each color in the two rows. LEDs were soldered up using 20ga solid core wire, wired in series and in 4 strings of 6 LEDs each.

warm white Cree XP-G
neutral whites and warm whites

The brains behind the operation is what really makes this light special! My initial plan was to drive the LEDs using pre-wired Buckpucks with a dimmer switch. But after talking to my good buddy Aaron (member: o2surplus on monsterfishkeepers), he convinced me to go with a custom driver and a microcontroller. The driver was built entirely by Aaron, so I take no credit here. In fact, if it weren’t for him constantly answering my noob questions, I probably wouldn’t have been able to go the DIY route. If you’re interested in a driver setup like mine, shoot him a pm, he may be able to build one for you Click the image to open in full size.

The LEDs are driven by four ON Semiconductor CAT4101 constant-current drivers. Each CAT4101 is controlling a string of 6 LEDs. 4 drivers running 6 LEDs, total of 24 of LEDs. Each driver controls an individual color; drivers 1 and 3 control the warm whites, drivers 2 and 4 control the neutral whites. The current to the LEDs is controlled by soldering an external resistor to one of the CAT4101’s pins. In this case, a 549ohm resistor was used for each CAT4101 to drive the LEDs at 1000mA, or 1a. The XP-Gs can handle up to 1500mA, so this is well within their safe operating range. For those who want to understand more on the CAT4101, you can find the technical specs here: http://www.onsemi.com/pub_link/Collateral/CAT4101-D.PDF

For dimming and on/off control, the CAT4101 relies on an external pulse width modulation signal (PWM). That is where the Arduino Duemilanove microcontroller comes in. To keep the microcontroller in sync with the on/off cycles, and in case the power is disconnected, the Arduino is connected to a DS1307 Real Time Clock with battery backup. The code I uploaded to the Arduino is set up to run sunrise-to-sunset lighting. The lights slowly fade on in the morning, and slowly fade out at night. Each LED string is fully adjustable for start time, photoperiod length, and brightness. This allows me to dim or brighten up the warm and neutral whites to get the color mixture I like. All I need to do is hook up the Arduino to my laptop and quickly edit the code. How freaking cool is that?!?!?

Custom PCB: screw terminals on top row are connections for the 4 LED channels. Middle row you’ll see the four CAT4101 drivers. Bottom left terminal is 24v power supply connections. Bottom middle terminal is 12v power supply for microcontroller and ground connections. Bottom right terminal is for the PWM signals from microcontroller, and for manual override.
24v power hookup and override switch
Arduino Duemilanove microcontroller (on inside lid of project box)
Arduino with real time clock module
Driver PCB and Arduino connected

This ‘magic black box’ that Aaron built me is really a work of art. The board is so neat and tidy. All the terminals and connections on the board are labeled. Everything is taken care of; the 24v power source hookup, the 5v power to run the CAT4101s, 12v power for the Arduino and fan connections, and the pins for the 5v PWM signal to the Arduino. He even included a power indicator light and an override switch to turn the LEDs on at any time, bypassing the Arduino. Only thing I needed to do was purchase the microcontroller and Real Time Clock and hook those up. So easy, a caveman can do it!

The project box, showing USB connection for microcontroller and LED hooksups
Other side of project box: 24v power hookup, LED indicator light and override switch

And last but not least, the power supply. Everything is powered by a 24v, 6.5a, 150w power supply.

24v 6.5a power supply

Thanks for reading Edition 2. In Edition 3, jcardona1 will be sharing his decor, water changing system and full tank shots, to continue on, click on this link: http://theaquaticgazette.com/2011/05/10/jcardona1%E2%80%B2s-wild-discus-biotope-3/

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credit: jcardona1

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