My DIY PWM LED dimmer - The Planted Tank Forum
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post #1 of 21 (permalink) Old 02-10-2010, 09:13 PM Thread Starter
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Lightbulb My DIY PWM LED dimmer

Admittedly, I don't have too much information in my initial post (it's at home), but I'm taking a small break from work and thought I'd see if there's any interest

Months ago, I created a LED lantern. The lantern idea itself was a flop, but as a result I ended up making a 2x2inch solid state controller that effortlessly controlled the brightness of 96 2.3 lumen 3mm LEDs. Power draw on this setup was about 28-30W, at 12 volts input. Admittedly, this isn't a ton of light, but I blame that more on my LEDs (and ballast resistors) than the controller itself. It uses PWM, running at a 900Hz frequency, and can control from 0-100% brightness. It takes a voltage input from 0-5v to produce that output. It seems to have TONS of room for more lighting, as my MOSFET was still cool to the touch, at 30W of draw, with no heatsink!

I'm happy posting any plans or pictures online that I have available to me (once I'm home). If there's enough interest I could get a group-buy for a fab house to make some boards. Parts cost is around $5-6, I don't know what the boards would cost to have fabbed.
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post #2 of 21 (permalink) Old 02-11-2010, 03:30 AM Thread Starter
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Maybe some pictures will get a little more interest? I'm not trying to make any money at all, I'm sorry if I put anyone off in my initial post I just wanted to share this and see if anyone else could use it.

The voltage range is actually between 0 and +V. This means that you can control the brightness in any manner you see fit -- I'm using a simple potentiometer, but you can use a photocell and resistor to make a light-sensitive voltage source. This would allow you to have the internal hood track the brightness of the sun outside, or by inverting it, have the internal hood maintain a constant light level in your tank despite other indoor lamps being on.

Here's a shot of its brightness (note, these LEDs have little to do with the controller I'm talking about, they are the leftovers from my lantern. I'd suggest a real planted tank use higher-wattage lamps, or perhaps halogens or something similar):


Another brightness shot:


The $13, 12v @ 3.5A power supply I'm using. It was cheap, that's why I picked it:


The underside of the board, shown with a 20oz bottle for scale. I made the board myself with a laser printer and radioshack parts


Topside of the board:


If nobody cares still, I'll let the thread die off. Otherwise, I can post the schematics of the controller (as the Eagle project files) and instructions for anyone who wants to make their own at-cost.
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post #3 of 21 (permalink) Old 02-13-2010, 11:26 PM
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I can post the schematics of the controller ...
Yea, I think you have to now.
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post #4 of 21 (permalink) Old 02-23-2010, 04:38 AM Thread Starter
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Well, I'm finally back from my business trip. I'd lost the original schematics and routings, so I've kinda slapped some together. The Eagle project files are available in the ZIP attachment -- as well as the full parts list, and where to buy each component. Component cost is just over $6. I'd appreciate if anyone wants to improve upon the design It's pretty small -- by just dragging the right side of the board over, you can shrink it to 2.1" square.

MOSFETs can handle a ton of current. At the relatively slow PWM frequency of 1khz, the MOSFET is "constant on" as far as the datasheet is concerned. It's on-state resistance of 0.06 ohms lends to just over 50 watts of power dissipation at 29 amps (regardless of voltage). Cool the MOSFET with a repurposed active CPU cooler for this kind of power handling. 29 amps at 48 volts is nearly 1400 watts of lighting -- you may find that a simple passive brick of aluminum is enough




BTW, the project is licensed under the TAPR open-source license. Read up on it here -- http://www.tapr.org/TAPR_Open_Hardware_License_v1.0.txt .
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File Type: zip PWM Controller.zip (48.8 KB, 1596 views)
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post #5 of 21 (permalink) Old 02-23-2010, 05:02 AM Thread Starter
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I came up with a few ideas for variable-voltage inputs for the dimmer. The VCC and GND arrows go to the smaller connector on the controller, and the double-bar thingy goes to the middle pin (the variable voltage itself). Hope this inspires someone ...

Feel free to ask questions

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post #6 of 21 (permalink) Old 06-19-2010, 03:52 PM
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Hello, Insta,

I realize a kind of late response but you’re post here was for me (initial) a reason to register on this website. I’m very interested in LED lighting/dimming. I have build a T5 compact dim (PIC) in my current tank (a modified Red Sea Max) and I want to use this circuit to generate a reference power that will regulate the brightness (is this understandable English? ;-)

The timer/dimmer circuit that I use now is a commercial product: Flora-mate. It is used to dim Tube Lights by analog 10v. However the device is not sending a voltage but is – and I hope you understand my English – is used to pull down the controllers dimsignal to 0. As you probably know this type of electronic controllers generate their own 10 volt. Actually the timer/dimmer is working as manual putting a shortcut wire on the 0-10v connection or a trimmer (potentiometer). Anyway the owner has given me the opportunity to use the original schematics to build my own model. I needed a much smaller model of the circuit to build it the hood of my tank. Look at the modificaties on my website. Since many people in The Netherlands are using this timer/dimmer I want to build for this timer/dimmer (under TAPR open-source license) an ‘add-on’ led dimming driver. A module that can be attached to the original model without the need to modify the original. So as much as possible people who do own the Flora-mate can use this module by simply connecting it.

As soon I am allowed to post URL's I will do! (goto 3w eliveld.nl - select 12 maart 2008 in Sitemap to read more about the Flora-mate) For now I just have a few questions:

I noticed that in you’re model a 900 hz is used to generate a ramp. Is this frequency not a problem in your household? Most ramp generators I know off generate between 100 and 300 hz. Any idea’s what effects could be on fish or plants? And any idea’s what kind of colour leds are best?

About the picture you published: as you mentioned is the eagle board not the same as the one on the photo. On the board many more capacitors are placed while on the photo a transitor is visible. In the schematic the capacitors are drawn. However its not clear why they are there. (just for flattening the power?) On the photo I see a blue trimmer (dont know name in English). Where is it in the schematic? And what is it for?

Hope to hear from you soon!

Kind regards, Erwin

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Last edited by E.Eliveld; 06-20-2010 at 03:26 PM. Reason: pointing to my website
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post #7 of 21 (permalink) Old 11-19-2010, 09:21 AM
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Can i use arduino to control the dimming? tq
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post #8 of 21 (permalink) Old 11-19-2010, 02:13 PM Thread Starter
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Hello, Insta,

I realize a kind of late response but you’re post here was for me (initial) a reason to register on this website. I’m very interested in LED lighting/dimming. I have build a T5 compact dim (PIC) in my current tank (a modified Red Sea Max) and I want to use this circuit to generate a reference power that will regulate the brightness (is this understandable English? ;-)

The timer/dimmer circuit that I use now is a commercial product: Flora-mate. It is used to dim Tube Lights by analog 10v. However the device is not sending a voltage but is – and I hope you understand my English – is used to pull down the controllers dimsignal to 0. As you probably know this type of electronic controllers generate their own 10 volt. Actually the timer/dimmer is working as manual putting a shortcut wire on the 0-10v connection or a trimmer (potentiometer). Anyway the owner has given me the opportunity to use the original schematics to build my own model. I needed a much smaller model of the circuit to build it the hood of my tank. Look at the modificaties on my website. Since many people in The Netherlands are using this timer/dimmer I want to build for this timer/dimmer (under TAPR open-source license) an ‘add-on’ led dimming driver. A module that can be attached to the original model without the need to modify the original. So as much as possible people who do own the Flora-mate can use this module by simply connecting it.

As soon I am allowed to post URL's I will do! (goto 3w eliveld.nl - select 12 maart 2008 in Sitemap to read more about the Flora-mate) For now I just have a few questions:

I noticed that in you’re model a 900 hz is used to generate a ramp. Is this frequency not a problem in your household? Most ramp generators I know off generate between 100 and 300 hz. Any idea’s what effects could be on fish or plants? And any idea’s what kind of colour leds are best?

About the picture you published: as you mentioned is the eagle board not the same as the one on the photo. On the board many more capacitors are placed while on the photo a transitor is visible. In the schematic the capacitors are drawn. However its not clear why they are there. (just for flattening the power?) On the photo I see a blue trimmer (dont know name in English). Where is it in the schematic? And what is it for?

Hope to hear from you soon!

Kind regards, Erwin
Goodness, Erwin, I'm so sorry to have missed your post!

If I'm understanding you correctly, you can in fact drive this dimmer straight from a Floramate if it outputs a variable analog voltage -- in fact that's the entire purpose of this circuit! It will require no modifications to do so. Use 10v as VCC, and feed the variable output into the input.

I chose 900hz just because it seemed like a useful number. It was completely arbitrary. Change C5 to change the frequency.

As for errata, the photos and the Eagle board are NOT identical, they just do the same thing. The photos are of the first version. I did make a few hardware changes since then. I removed a trimmer and replaced it with fixed resistors. I did add more filtering capacitors -- large electrolytics to help with sags when the driving op-amps change state, and small electrolytics (or large ceramics) to help control ringing. They're just for stability. The transistor in the original was to fire the MOSFET -- turns out its better to just let the op-amps do that for as low of a frequency as I'm using, since they both push and pull at a few milliamps (enough to switch the FETs on in a few microseconds).

Incidentally, I used a larger version of this circuit (at a 50khz frequency) to power a flyback transformer. By feeding music into the voltage input, I can make musical arcs I actually made my own MOSFET driver for that, with a 4011 quad-NAND gate driving two 2N2222 transistors to slam the MOSFET gate open and shut. But I'm also using an 800V 10A FET...

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post #9 of 21 (permalink) Old 11-19-2010, 02:54 PM
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Can i use arduino to control the dimming? tq
yes, there are a few PWM outputs on the board.


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post #10 of 21 (permalink) Old 11-22-2010, 01:07 PM
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can i just connect the pwm to the board v_signal?
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post #11 of 21 (permalink) Old 11-22-2010, 04:28 PM Thread Starter
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You really need to not use my dimmer with your Arduino. Just use a low-side driver like I said in PM. I don't have time to redraw the schematic from the design notes for whichever one you pick.

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post #12 of 21 (permalink) Old 11-23-2010, 03:28 AM
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Thank you for the reply, i'll try the low-side driver like you mentioned in PM. About the capacitor, can you tell me whare do the 2 100uf capacitor go in the eagle board. which is the 16v and 50v? is it C1=16v and C3=50v or the other way around. tq..

1 - $0.15 - 3w.allelectronics.com/make-a-store/category/140100/Capacitors/Electrolytic-Radial/1.html (100 uF, 16V)
1 - $0.30 - 3w.allelectronics.com/make-a-store/category/140100/Capacitors/Electrolytic-Radial/1.html (100 uF, 50V)

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You really need to not use my dimmer with your Arduino. Just use a low-side driver like I said in PM. I don't have time to redraw the schematic from the design notes for whichever one you pick.
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post #13 of 21 (permalink) Old 11-23-2010, 04:55 AM Thread Starter
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C3 was the 50v cap. It's incase you run higher than 10-12v for the LEDs.

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post #14 of 21 (permalink) Old 11-23-2010, 11:15 AM
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Ok... thanks bro. insta... gonna build the board and try running it with arduino. i'll update this thread once its finish. thanks for the good DIY idea.

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C3 was the 50v cap. It's incase you run higher than 10-12v for the LEDs.
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post #15 of 21 (permalink) Old 12-11-2010, 09:03 AM
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Thanks for the reply, it seems now that its my time to be late ;-)

Next year I will start to modify second RSM , for now I started to disassemble it and I'm looking around for the LED's.

Erwin

Digging in hard ground is more relaxing to a worm than fishing. (the journey is the destination: veni etinam)
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