Dual Led lamp control circuit

Discussion in 'The Projects Forum' started by FMz, Feb 20, 2018.

  1. FMz

    Thread Starter New Member

    Feb 20, 2018
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    Hello,

    I'm in the early planning stage of this project, no parts/quantities have been selected just yet. (It's for a fish tank light). I have background with electronics, in the automotive sector, but not as designer. I've never experimented with transistors so far, and watching tutorials isn't working for me, I need to play with it, but unfortunately I don't have any on hand right now.

    I need a bit of help to figure a way to control two blocks of LEDs. One block has first priority, and is made of white LEDs, either 1 or 3 Watts, and the other is made of blue LEDs of the same W.

    The way I want it to work is this:
    The white LEDs would be binary, either off or full brightness.
    The blue LEDs would be either off, 40% on or full brightness.
    I want the blue light to be either dim (or off, whichever the easiest) when the white light is on, no matter where the switch is for the blue light.
    I have done something similar before, a bunch of wires, resistors, and relay held by cable ties, where the relay would cut the power of the blue LEDs whenever power was applied to the white ones. The cons of this are mainly the noisy relay, and the crude MO. I'd like a bit more refinement on this project.

    Some of the features I'd like are:
    Like I said above, have the blue LEDs on dimly when the whites are on (I prefer that look in my tanks)
    Fade-in when switching on (and from dim to bright in the blue LEDs' case)
    Silent and simple operation/circuitry (no programming experience).​

    What I figured so far is I will be using a 12V DC power supply, as I have tons on hand I'm not using, and I want blocks made of a resistor wired with a pair of LEDs and put as many as I want of these blocks to scale the lamp for various size aquariums, from my mum's 5 gallons to my big 6 foot tank and every other sizes. They would have common positive, switched ground, and the dimness controlled by a generic PWM module.

    Thanks for reading
     
  2. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    By "pair", do you mean one white and one blue?
    Current per LED?
    Led part numbers?
    Link to datasheets?

    Your problem description is not clear. How many switches/buttons do you envision for controlling things.
    One - two-position for White - On/Off - yes/no
    One - three position for Blue - On/dim/Off - yes/no
    Fade-in time period?
    Fade-out?

    Blue off whenever White is on is definitely the easiest.

    Max total current for Blue LEDs? This determines the dimming technique, and whether or not you need a heatsink or small fan.

    ak
     
  3. FMz

    Thread Starter New Member

    Feb 20, 2018
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    As I said in the begining
    I have been looking around, These are 1W LEDs that I'm likely to use.
    Color - Temperature - Voltage -- Current - Lumious Flux - Lens Angle
    White - 4000-4500k - 3.2-3.4V - 350mA -- 100-110lm --- 120
    Blue --- 460-470nm -- 3.2-3.4V - 350mA -- 35-45lm ------ 120

    By pair I mean a two of the same colour. I could the choose how many blocks of each colour to use for a given tank depending on the size.
    One one off switch for white, probably in the form of a wall timer and a 3-way switch for blue. 2 second fade-in and -out.
    Even though switching off would be easier, I want to find ways to get the dim blue light when the white's on. I'm trying to gain more knowledge and push my current limits one step at a time.
     
  4. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    So far, nothing you have described will be difficult. Running the numbers for an LED pair, 12 V source, 0.35 A, 6.6 V across two LEDs,,,, the series current limiting resistor is 15 ohms. It dissipates 2 W, so you'll need a 5 W part. A better way would be a switching power supply with a constant current output adjusted to 0.35 A, but we can work with what you already own. But note that 0.95 W per LED will add up quickly as a heat blanket over or around the tank.

    If you go to 3 LEDs per module, the resistor drops to 6 ohms, 0.74 W. Now a much smaller 2 W resistor will do the job and run cooler. The heat blanket will be 0.25 W per LED, 74% less than above. Also, for the same total number of LEDs, the PWM device will be handling 33% less current.

    ak
     
    Last edited: Feb 21, 2018
  5. Jonlate

    Member

    Dec 21, 2017
    75
    3
    What sort of fish do you have? Fresh or salt? Planted or not?
    Keeping fish myself there are so many different light needs depending on what you are keeping.
    If you want ultimate control you are best buying a off the shelf one.
    A1prime/hydra, GHL midras, ecotech, maxspect. These give you the kelvin rating, power used, etc

    If you want to try a diy version, have a look at this. Just make sure to make it water proof, just Incase you drop it in the tank when cleaning!!
    https://www.irishfishkeepers.com/forum/41-diy/135980-140x30cm-diy-led-light-115w-fresh-water-tank
     
  6. FMz

    Thread Starter New Member

    Feb 20, 2018
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    Yes I agree that part is pretty simple, the part that I'm trying to figure out is the switching, how to switch the blue light automatically when power is applied to the white ones? I think maybe transistors, but like I said in the op, I don't know enough about them to be sure if it would work. I've read somewhere about fading with capacitors, but that was a while back, I can't find it back atm.

    Jonlate, I have a 6x2 planted, currently sitting dry due to travels, and I plan on a 8x3 Borneo-inspired paludarium in the next couple of years. lights will be mounted in the hood.
     
  7. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Capacitors are involved in the ramping up and down of brightness, because a resistor-capacitor combination produces a voltage or current slope (increasing or decreasing ramp). Lotsa things go into the shape and timing of the slope, but them's the basics. At your power levels, using a capacitor directly to cause the brightness to ramp would take a huge capacitor.

    It is easier to work through the switches and control functions if the switches do not actually switch power, but just the control signals to the power parts. For example, the White switch can send a signal to the white power supply to come on 100%, and that same signal can be manipulated to tell the blue power supply to go to 50%.

    Talk about these power supplies. Manufacturer, model/part number, ratings on the label, photos ??? Since you already have them, their characteristics will drive just about everything else in the design.

    ak
     
  8. ebeowulf17

    AAC Fanatic!

    Aug 12, 2014
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    I'd be curious to know what off the shelf PWM modules are being considered too. Do you think there's any chance that a PWM controller that allows for a remote knob could be manipulated with an external voltage ramp to modify its duty cycle? It would be nice to achieve the ramps without lots more power dissipation.

    Just thinking out loud - no idea if this is even a realistic possibility, much less a good idea!
     
  9. FMz

    Thread Starter New Member

    Feb 20, 2018
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    All this is nice, but what I need help on is figuring out the switching. Once I have a basic circuit drawn, it can be adapted to virtually any spec LED and/or power supply.
     
  10. -live wire-

    Active Member

    Dec 22, 2017
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    Just a suggestion, espescially if you want to add more stuff or make it more complicated, try using a microcontroller like arduino. You can easily program things to do almost anything. Just maybe use some mosfets if you really need higher power LEDs.
     
  11. ebeowulf17

    AAC Fanatic!

    Aug 12, 2014
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    You say that now, but in your earlier posts you were asking for fading and dimming:

    Different user requirements will lead to different solutions. If you can decide what you want, you'll get better answers.

    Anyway, I should back out of this one. There are enough layers to this problem that I know I won't have the best solution. I'll be watching with interest to see what @AnalogKid (or any of the other experts here) comes up with. Cheers!
     
  12. FMz

    Thread Starter New Member

    Feb 20, 2018
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    Look back, I said the way I wanted to work, and followed with a different section of things I'd like if possible without programmation. The fading is optional, it's more of a whim than a need. As for the dimming, I stated in the first post that it would be via PWM, so that's not the problem.
    I want a solution for the switching between modes:

    Blue switch can be in either position, between off, dim, and bright. When white is powered, the blue goes to dim mode, then returns to its previous setting once the power is removed from the white LEDs.
     
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