Automatic, Biorhythm LED Aquarium Light




Normal aquarium lights are fluorescent tubes that require that you turn them on in the morning and off at night. This isn't the most efficient way to light a tank, but for some reason it's the default kit you get. Another issue is that the high-voltage circuit that powers the bulb is loud!

Also, in my house, we inevitably forget to turn on the light in the morning, or we turn it off way too late in the evening, and that means the "day" for the fish is always a little off. Considering that these are living creatures that base their life patterns on the sunshine, I always thought it must really be messing them up.

So this project had a couple of main goals:

1) Replace the fluorescent light with something that is quieter and more energy efficient
2) Come up with a way to vary the light intensity with the natural sunlight outside
3) Package it all within the existing light hood

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Step 1: Materials

1 - Existing fluorescent aquarium hood
4-5 feet - Braided steel picture hanging wire

1 - Amtel ATMega168 Microcontroller
50-70 - High Intensity, White LED's
3 - 1M resistor
1 - Potentiometer
1 - Light Dependent Resistor
1 - Push button switch (SPST, default off)
1 - Project board
1 - 7805, 5V voltage regulator
1 - IRF510, N-Channel Power MOSFET
2-4 feet - copper hookup wire
1 - 12V power supply (at least 2A, whatever you have lying around)
1 each - Male and Female headers

Wire cutters
Soldering Iron
(All the basics)

Step 2: Modify the Existing Hood

The first step is mainly about throwing away the old stuff. Happily, my fluorescent bulb was already going out, but the electronics weren't. I'll save those for some other future project. Otherwise, clean it out!

Next you'll want to drill holes to allow for mounting the electrical wires. We'll mount these using threaded aluminum posts... this way, the outside modifications to the hood aren't noticeable. While I want this to be a great mod in the end, I still want it to fit in the living room as it always has. Make it look professional!

The spacing of the holes isn't terribly important. For me, it was 3 inches. The actual spacing for you will be based on the size of your aquarium hood and the size of the project board. It might be a good idea to read through all of the instructions to get an idea of how to determine the spacing in your case.

Step 3: Installing the Main Wiring

So the main idea here is to mount two lengths of the braided stainless steel picture hanging wire parallel to each other. One will be positive, one negative. The LEDs will be strung between, allowing you to add more LEDs if you want more light.

I got four threaded aluminum posts with matching screws from Lowes for under a dollar each. Your mileage may vary, but they shouldn't be expensive at all. Mine are 3/8" long to allow for some space when installed.

That space comes into play when preparing the cable. You'll want to wrap it around the post for about 2 wraps, then pull out the post, keeping the loop in the cable. You can see it below in one of the clips of my helping hands. I soldered the wire to keep it solid. Since there will be tension applied to it, make sure your method is just as stable.

Getting one end done is a cinch, but the other side takes a bit of skill. You want to install the cable on one end, and then the remaining post on the other side. Now, wrap the loose cable end around the empty post, trying to keep enough tension. You want each cable to be fairly tight between each end.

Step 4: The LED Array

When i first began the project, I figured a dozen or so high-intensity LEDs would be plenty. After all, perusing the LED lighting aisle at the local hardware store found several 4-LED lights that made everything very bright.

The difference appears to be that we're shining the light through water. Strangely enough, that takes a LOT more light than you would otherwise expect. I tried it initially with 8 LEDs, and the brightness was negligible. I then experimented with other numbers, and it quickly became apparent that I needed MANY more. How do you cheaply acquire lots of high-intensity LEDs?

I found a $10 LED spot light at a local store that did the trick. It had 60 of the little guys all installed in a series, so I only had to desolder them and they were mine!

Once I had all of the LEDs I needed, I began soldering them together. Since I knew I was going to power the whole thing with 12V, I knew I needed to install no less that 4 LEDs in series That will provide 3V each, which is under their 3.3V max. Yes, that means I'm not getting every single lumen of brightness, but it turned out to be just fine in the end, and I know I'm not overpowering the individual elements.

I took a piece of basswood and cut holes for a template to hold the LEDs. I then went through and soldered about 4" of light gauge copper wire across their leads. This proved to be the quicker way to do it, rather than soldering each individual wire on at a time. After soldering the wire across, I snipped out the 1/16" or so that was between the leads.

Afterward, install the LEDs between the power cables as you see fit. Again, this is very dependent on your particular application, but I provided a picture of how I did it below.

Step 5: The Electronics

I've been holding off on posting this instructable because I wanted to provide a proper schematic, but I don't really have any software that makes that step very easy. To be honest, half of the hardware I installed below isn't necessary, and it was used while I was developing the circuit.

Since using an AVR microcontroller is out of the scope of this instructable anyway, and you would need existing experience, I'm hoping that providing the firmware (attached as 'main.c' below) will be enough to get you going. Of course, if there are any questions, please ask and I'll help as much as possible.

Suffice it to say, the signal for controlling the LED array is connected to pin 12 (PD6), the 'temporary off' switch is connected to pin 4 (PD2), and the LDR is connected through a voltage divider to analog pin 23 (PC0). I set up internal PWM, and simply change the PWM value based on the LDR analog reading. It's probably pretty messy, but it was my first real project with the AVR by itself. Any suggestions for improving the code would be welcome!

Step 6: All Done!

In all, I'm very proud of the way this project went together. It took 10-15 hours in the end, mainly in experimenting and planning, but it paid off. Replacing the high-voltage driver and fluorescent tube with a small 12V power supply and efficient LEDs makes a huge difference in power consumption. I wish I had a kill-a-watt to test the before and after and give you absolute comparisons, but I know it's at least a good improvement. Not only that, I won't have to replace the bulb every 6 months when it burns out. While it's only a small improvement environmentally, it's better than nothing!

In addition, we never have to touch the light manually now. This gives us the assurance that the fish are setting their rhythms based on a regular light cycle, rather than the 'whenever we remember' phases, hopefully lengthening their lives. It also means we can go on vacation without having to worry about the fish light. Plenty of positives.

Possible Improvements
1) One thing I considered was adding a 'feeding light' to the outside of the light hood. This would light up when it was feeding time, and allow us to dismiss the light for that night with a button press. Since everyone in the family feeds the fish, it would keep us from feeding them too much.
2) I also considered adding an auto feeder into the mix. If I do that, I'll post a second instructable with the steps needed.

Though I've been a member since 2006, this is my first instructable so far. I hope to post many more as time goes on. Please give me feedback on things I didn't cover enough, as I'm always looking to improve!

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    22 Discussions


    7 years ago on Introduction

    thanks for your perfect post would you post schematic , if you don't have program i can help you. i would be appreciate if you send handy drawing model to my E-mail and i will draw schematic and send circuit back to you for sharing

    1 reply

    you should prolly delete your e-mails on here Private message them to him.. There are spam bots that look for this. next thing you know you are overwhelmed with spam.


    9 years ago on Introduction

    I think this instructable is awesome, especially since I have little knowledge of this type of electronics. I was wondering how would I go about making this into a timed based system instead mimicking the natural light outside? I don't keep my tank close to a window nor do I want to string that long of a cable to a window. I want the light to slowly turn on and off over the course of 30-45 minutes and turn some moonlights off and on an hour or so later/ before. Any suggestions???

    1 reply

    Reply 8 years ago on Introduction

    Old post, but I think you could just use the micro to "dim" the lights by turning them on and off super fast (like >1kHz) and adjusting how long they were on vs off. This is called the "duty cycle", and it's a common control for LEDs. You'd also have to adjust the code so the micro knew what time of day it was. I am not familiar enough with these to know if their internal clock will even keep accurate time for a day, so you might need an external part to keep time. You'd also have to have some interface for setting the time, something like a reset button, or an hour/minute button.


    9 years ago on Introduction

    I really love this Idea of lighting. Would it be possible to get a copy of the schematic or a drawing of the breadboard model. I am not electronic savy, and would need as much help as I can get in doing the electronics. I would like to build this lighting system for my aquariums.  Thank you for this instructable.


    10 years ago on Step 5

    Sorry, I'm new to this site and didn't see anywhere that I could edit my comment, but I have a question now. What is it that you pointed out that you left on the PCB but don't use anymore? Is it an AC or DC plug?

    Also, I may be missing something completely, but you have the firmware included, but is there no place to see how this curcuit is wired? I mean, I can see you have a switch and a resistor, maybe two, looks like maybe an IC, a jumper and a few other things, but I'm just not getting how it's wired. I know you said you have no place to create a schematic, so I gave you the link to that freeware(it works really well by the way), but as somebody esle pointed out if you could just throw a drawing on a piece of paper that would be awesome. I am really interested in doing this.

    Also, the LED's you ended up using you said were put together in series, so when you took them apart you didn't have to re-solder them right? All you did was put the LED's you already had in series and then put those in paralel correct?

    Another  thing. Since I don't know how this is wired  or anything, do you think it would be possible to add in moonlight that would gradually increase and then decrease just like the daytime lighting?

    Sorry for all the questions, I'm just really interested ini this. 

    3 replies

    Reply 10 years ago on Introduction

    Thanks for the questions!  I appreciate the link to fritzing...I'll try it out and see if I can get something posted for you.

    As far as the unused component, you're correct, it's a DC plug that Iwas using for power while I was working on the circuit on mybench.  I left it there in case I decided to pull the board out tothrow in more changes.  As it is, the braided wire provides powerto both the circuit and LEDs at the same time.

    For the LEDs, indeed I DID resolder them.  Take a look atthe photos and you'll see what I mean.  I soldered several stringsof 4 LEDs in series, and then wired all of the 4 LED strings in parallelwith each other.  That means 12V is provided to 4 LEDs at a time,for 3V each.  As long as your power supply is a steady 12V, thisshould be fine.  YMMV.


    Reply 10 years ago on Introduction

    Where did you find that stinkin LED flood light. I've spent two daystrying to find one. Looks like if I want to complete this project I'mgonna have to dig into my bulk bought LED's 

    I'm not sure how this site works, but I'm planning on making a fewchanges to your design for safety and usability. For one I have touse insulated wire to put the LED's on. I have been designing andmanufacturing electronics for some time now and looking at that makes mecringe lol  I'm gonna use a single core copper wire it will beanywere from 14 to 22 AWG and insulated. I'm also going to cover thoseflat nuts and bolts that you have on the side of the lid so I don'tshock myself. Just an idea for ya


    Reply 10 years ago on Introduction

    I forgot your last question...

    I'm not sure if a moonlight switch would be possible or not, at leastnot in the same way.  I'm not sure if an LDR is sensitive enough todetect the moonlight, and I definitely think you could have issues withstreet lights or other outdoor lighting causing it to getconfused.  Since the sun dwarfs these, it's easy enough to filterout the less intense light.

    That being said, as I mentioned in one of my other comments, the IRF510seems to have a certain amount of bleed voltage when at 0 in my case, sothere is definitely a slight 'moonglow' at night with mine, it justdoesn't change intensity through the night.

    Incidentally, I've been using this setup for a solid 6 months, and havehad ZERO side effects on either plant life or fish life.  The tankseems to be perfectly happy.  I hope it works out the same for you!


    10 years ago on Step 5

    If you'd like to publish a schematic or a drawing or a breadboard model try this    that may do what you want


    10 years ago on Step 6

    You have to remember that LED light is not suitable for most aquatic plants (don't bother if they are artificial ;-)), otherwise excellent job. (if you've got no plants, remember to change water on weekly basis about 20-30% a week. might be tap water) Also you can think about night light, 1-2h after main is switched off. For example 5 blue LEDs... Cheers.

    5 replies

    Reply 10 years ago on Introduction

    Initially I would agree about the plants, but I'm honestly not sure... do you have more information? If you see the first comment and my reply... I haven't been able to find any information to say that LED light is any better/worse for the plants at all. I did find several LED "plant light" products though... so apparently they can be tuned to get the right balance. As to your second point, very true! In my case, when I brought the signal of the IRF510 to 0, it allowed a bit of bleed voltage (I don't know if mine is defective, or if that's expected and you have to negative bias it?) which gives a very faint glow. Simulates moonlight quite well.


    Reply 10 years ago on Introduction

    Hi, sorry for delay in answering. Output light from LED is monochrome, in some circumstances that is ok, (car light for example). For human eye there's no difference, for plants the difference is HUGE. here is basic article about photosynthesis, but you can find plenty of them on wikipedia or Internet.
    Anyway, I haven't seen any serious planted tank setup with LED light.
    Probably for some less demanding plants LED lights are fair enough, not for all definitely.


    Reply 10 years ago on Introduction

    It might be tempting to use tricolour LEDs to create a certain colour of light from the red, green and blue components, but that would be unwise because that is really only a simulation and will have huge ranges of the visible spectrum absent (possibly excluding critical wavelengths for plantlife). "White" LEDs, on the other hand, should be OK because they are not monochromatic at all. They are actually a blue or ultraviolet LED "chip" coated with a scintillant that glows in a fairly broad spectrum in almost exactly the same way as a fluorescent tube does. It's probably far from an an ideal solution, but white LED's should be pretty right.


    Reply 10 years ago on Introduction

    Actually I'm testing at the moment luxeon LED's as a source of light. They are 2 x 3W white (very small tank, rather jar than tank, without CO2 only easycarbo as a source of carbon). So far exactly as I expected, some demanding plants not growing as under normal T8/T5 light tubes. For other plants like java moss its ok, more or less the same growing ratio. I'm going to set up small tank/jar with glosstigma next week and see what happen.


    Reply 10 years ago on Introduction

    White led alone may not be suitable for plants. But what if you also added red and blue led's to match the Florescent lamp's spectrum?


    10 years ago on Step 5

    I agree, great article. Looking to build a "reef capable" LED based lighting system. Any help of course much appreciated. But again way to go!


    10 years ago on Step 5

    Hi, this is great article but would be even greater if you could publish the schematics. ;) Just try to draw it yourself to a piece of paper and scan it. Should be good enough.


    10 years ago on Step 6

    How could this be adapted for a small saltwater aquarium. I think the LEDs need to have another spec.


    10 years ago on Introduction

    Do you get the right frequency / intensity distribution from the LEDs? I'd always thought that the aquarium tubes were expensive because they're designed to produce the right balance of light, but I know little more than this.