206 replies to this topic

[andre21]

hello i am new here. i find it very interesting.Spacilly the LED idea was great. Now i am curious about the voltage. how much power it will take to run it? Are you talking about the fish aquarium? i want to make a project like you do. can you give me some tips?

[mcinnes01]

Shakey at the bottom is a very undesirable feature with LEDs, thats a real shame.

Thanks for keeping me up to date with the NCL driver and its progress, you've saved me a lot of time.

I feel your initial driver solution sounds the most reliable, so I think I am going to follow suite and have a go at making that one.

I will get a shopping cart together and post it for you to give it a once over if you don't mind.

Also just to refresh your drivers provide 3 channels per attiny, and each of these can be independantly controlled? Is this done by having 3 PWM signals going in to the attiny?

Finally we discussed inductors in length and I have some coil craft samples but am a little unsure of which are which, the attiny require 1 inductor @ 100uh right? Is that likely to be the smaller ones on the right in this picture with 101 written on them? These samples were the 100uh for the attinys and the 33uh for the NLCs (the larger ones on the left have 333 written on them.



Thanks in advance,

Andy

Andre21,

Welcome to the forum!

This project is for an aquarium lighting enclosure, Magpie who is a key contributor is already sucessfully using one of the drivers discussed in his own projects for low power domestic lighting, so this information should be useful for most LED projects.

I would like to say this project is much further on, but in reality I've have spent a fair bit of time investigating the LED drivers and the dimming control, also with the release of the netduino GO I have decided to completely rethink my project in a more modular format, so it is still in the testing phase at the moment.

If you are interested in aquarium lighting/ control I would recommend having a go a building Magpies first driver from this forum using the AtTiny chips, you can look at dimming with the chips in various ways and this really comes down to the complexity you want in your aquarium. For example a simple aquarium lighting controller could have 30 3W Leds (go for decent cree LEDs for efficientcy and lumenums) you would then have a mix of royal blues and bright whites say 15 white 15 blue. Technically you could split these in strings of 5 accross 2 drivers and you would get a really efficient aquarium lighting enclosure with 6 channels of control. However I never seem to make life easy (or cheap) for myself and I am going for a less efficient more expensive approach of 1 LED, 10 drivers, 30 channels. This will allow me to do some effects such as cloud cover and lightening.

If you want to start a project like this, I would suggest getting some LEDs and build a driver and some way of controlling the brightness. Once you are happy with the setup start looking at driving all the LEDs and how you are going to power them. In terms of power the main thing to consider is voltage drop and protecting your sensitive LEDs from over current. One way to do this was suggested by Magpie, by building an additional circuit. If you have string of 5 LEDs and each LED had a voltage drop of 3v you would look for something like 18v -24v power supply.

hth

andy

[Magpie]

It looks like 100u and 33u as you say, I don't know why the marking is inconsistent. I am doing a redesign of my Attiny dimmer. I have just about decided on a schematic, I will let you know when I have more. I have finally sorted out the key role of the inductor, when you need it and when it is just desirable. It was never really clear in my head, finally it is clear, after all I am an EE, I should know better, it is actually quite obvious. You don't need the inductor when you're LED string can handle the full rail voltage continuously. eg. 4 x 3.2 volts leds at 12 volts. If they can't handle the continuous current then you need the inductor and you need to switch the supply (as in a buck converter) so that the LEDs are not overloaded. The smallest inductor you can use will depend on the switching frequency, the input voltage and the LED strings"V vs I" graph. It is hard to calculate exactly, but you would want to allow for a reasonable margin anyway, so an exact calculation is not necessary, just use bigger. I am thinking of either 64khz - 256 khz and therefore probably for me up to 470uF, but for you running off 12 volts the 100uF will probably be plenty. I will post as I have more info.

[Magpie]

I have decided on a rough schematic, I am using the negative input as common again.
The details are on my domestic lights project . It is based on the Attiny but with some improvements.
I hope this helps.<br>

Edited by Magpie, 17 June 2012 - 06:46 AM.

[mcinnes01]

Ahh cool I will get on with your AtTiny driver asap, the link you provided doesn't seem to be working though?

Thanks again,

Andy

EDIT: Found the link http://www.eevblog.c...ighting-project

[mcinnes01]

Do you have an updated BOM or even maybe, possibly.... a list of part numbers? I really like the idea of this driver it seems a really nice way to control the LEDs, I'm hoping to eventually implement a nice library for the leds so I can do commands like: Leds(ChannelArray, IntensityInteger, FadeTimeInteger); Also do you have a schematic of the new version of the driver? In terms of the over current protection circuit and the the Black regulator, have you got a schematic that includes all of these connected together and again perhaps part numbers? Many thanks, Andy

[Magpie]

I am drawing a schematic to lay out a board, but it will be for 24-48 volts input. You don't need the black regulator it is only to drop the voltage down from 24v to 12. My understanding is you will be using 12v input. I have actually made up a 3 transistor black regulator on a bread board and it did work as expected. I will be using a 2 transistor regulator to drive the 12volt rail with no current limiting. I only need a small amount of power at 12v. Then from 12volts I use a regulator to bring it to 5 volts. Obviously this step loses 7/12 of the power. As far as the bom goes just look on the schematics. I am wondering if down the track I should use the attiny25 (8 pin) and just do one channel per micro, this may suit you better, but for this version I am using the attinyX61a 20 pin. Maybe what you should do is a block diagram of your entire system. Maybe you have. This can really help you see things once its gets complicated. Then add a couple vero board prototypes to a couple of channels and see what works best. I will post a schematic with micro attached soon, I want to send it to the manufacturers soon. Hopefully 1 week.

[Magpie]

Yes you could change it to 5 volts maximum. I have changed my input protection, to at TVS diode and a fuse. and got rid of the mosfet. You can do the same. If you wanted to make it a sort of 5-12 volt combo that probably would be best. It would give you the option to have more than one led per channel if you want it. I don't think the efficiency loss would be too bad. Just get rid of the 24-12 stuff, then you have virtually the same circuit as me. It may save a bit of testing. Alternatively you can move the fet down to 5 volts. you would need a logic level fet. and you could get rid of the bc547s and associated resistors. Just like AHellenes diagram. If you did this there would be no point in using a linear regulator to get the 5v for the mosfet drain, it would just be a waste of power, but the regulator for the 5volts to the micro would be still necessary. If I was you I think I would go the 5-12 volt combo. I am currently selecting Parts from Digikey for the boards, for the first time I will be able to give you a real BOM and even Digikey part numbers as well as Manufacturers part numbers. Do you have anyway of programming the Attinyx61? I am not sure whether to go with the Dip20 or the Soic20, (Actually I will go Dip) I think I am going with Murata 4 pin torroids for the inductors @ about $1.80 each. The only problem is their height which is about 15mm at a guess. And which connectors for the led sting, I used green phoenix connectors on the Steff shield. Have you got any good 2 way connectors say 3 amp max. Less than 15mm height. You can probably use my boards if you want, with a couple of hand modifications if you go 5-12, I will make sure that you don't have to cut tracks if you want. I will put in a jumper before the black regulator and you can wire that straight to 12 volts.

[mcinnes01]

Ah cool,

Yes the 5v/12v sounds fine, it gives me a little option if and when (its inedvitable really) that I get another larger tank!

I have an avr ISP mk2 will that do the trick?

I noticed on your schematic you have the 861As, is your program too big for the 461As?

Diode and fuse sounds better and cheaper than a FET.

I was contemplating the same dip or soic and I thought until I have something up an running theres no point complicating things with surface mount.

I look forward to your parts list.

In terms of connectors that is a good question :

smaller than jst
jst
polarised
screw
my favourite

[Magpie]

All my parts will be surface mount where possible. If you want to go dip you will have to find similar.

But the Attiny will be Dip, just so I am sure that I can program it, I have never done an ISP header before and a cock up here would be catastrophic, the big inductors will be dip, and the connectors and fuse holder.

I think the program will be very small, probably the tiny261 will be fine.

I have an avr ISP mk2 will that do the trick?

I assume so but I really don't know.

Those connectors look good (your favourite).

I think I want the screw in onthe flying lead and the L shaped black header pins, probably I will go for 5mm.
I will draw the pcb at 5mm.

[Magpie]

Hi I have all but finished the board for the Steff2, attiny version. I also have a BOM, I will post soon, I am at work now. I will probably send off to seeed studio or similar this week.

[Magpie]

Hi I have all but finished the board for the Steff2, attiny version. I also have a BOM, I will post soon, I am at work now. I will probably send off to seeed studio or similar this week. The board picture is attached, the inductors haven't got a 3d model, they are vertically mounted torroids. Either 100uH or 220uH, probably I will try both.

Attached Files

•  steff23d.png   61.57KB   23 downloads

[mcinnes01]

Nice! Well done! Love the sea spark logo are you getting that on your silk screen? The bit in the bottom right corner is the black regulator right? Andy

[tlmiii01]

I know I am jumping in a little late here, but I just looked at the picture with the inductors. Aren't the ones on the left actually 33mH instead of 33uH? Thomas

[Magpie]

I know I am jumping in a little late here, but I just looked at the picture with the inductors. Aren't the ones on the left actually 33mH instead of 33uH?

I looked at this link coilcraft series

I must admit I don't know.

The bit in the bottom right corner is the black regulator right?

that's right.

ps. I changed the logo, it will come out on the silkscreen.

I almost mounted the torroid footprints upside down, that would've been a disaster.
I just sent the gerbers off to seeed studio last night.
If you want I can send you some, I will test them first though.

[Magpie]

Here is the final schematic for the first spin and the BOM. The 0805 resistors I didn't bother getting the part numbers for. Same with some of the others which I already have. BOM was wrong, it has been corrected.

Attached Files

•  Steff2 Schematic.png   45.6KB   10 downloads

Edited by Magpie, 07 July 2012 - 01:57 PM.

[mcinnes01]

Hi Magpie, Thanks thats amasing, can't wait to see your finished board all soldered up! I was just looking through your schematic and BOM and was trying to work out which parts I can omit on my order.... I went through the whole BOM and black regulator and have highlighed the parts I think I can do with out in red in the attached. The regulator also provides your 5v right for powering the attiny etc right? Do you think this side of the circuit can be powered paracitically off the netduino and if so do you think skip the 5v regulator as well? Also C19 - C22 aren't on the BOM do you know what these are, not sure if there is anything else? Also one of the resistors is marked as a bit wide, is this the foot print or the value and does it matter? I'm going to go SMD too, I think it will be better especially as you said in terms of getting resistors close to the attiny. I wondered if there is anything else I don't need on the board, oh and which resistor numbers/ other parts would need changing to base this on the 1 LED per channel 3.15v 700ma? Do you thinking running the whole circuit at 5v would be more efficient for 1 LED per channel than running a 12v? I suppose if I want to lengthen my LED chains latter I could swich a few parts out right? Perhaps even provide a jumper option, where by you can select 5v or 12v and swap out the power supply accordingly? How many ma are your running your Crees at in this circuit? I'm thinking about how I want to lay my board(s) out for this, all 30 channels on 1 board and the board sits above the LEDs and the LEDs cables plug in to the main driver board with connectors, or split the drivers it to 10 x 3 channel strips as there will be 3 LEDs in a row in my LED enclosure or even split the drivers off the board from the attinys, then have the 10 attinys on 1 board and the 30 led drivers sit right above each led with wires connecting back to the board with the aattinys on? Fantastic work! Andy

Attached Files

•  Steff2 BOM.zip   9.81KB   1 downloads

[Magpie]

Hi

Thanks for pointing out the missing caps from my BOM, it was also missing R1.
All the caps are just decoupling or filtering caps of 100n 0805 and the Resistor was just a 10k 1206.
I cant believe I made this mistake, It just goes to show how easy it is. I am definitely not a computer.

I haven't gone exhaustively through your list as it seems your not quite decided the best way to go anyway.

As far as boards go I would go the modular approach, so if a board fails you can have spares, x channels per board.
Maybe 3, maybe 8, maybe 16. Design decision.

Also that way you could have some boards at 12 volts some at 5.

Actually on the subject of design decisions, the way just about every project I have worked on has been is that you never design it right first time anyway.
So there is no point trying to perfect the initial design. The moment the first working version comes out, somebody sees things that they hadn't noticed before.

So I think,

• Get something out there,
• Get something out there that isn't impossible to change or fix.
• Keep changing it till you think it's right.

If you go the small number of channels per board approach, you can chop it and change it. fix it without turning the whole thing off.

I am writing as I think so the conclusion of what I think you should do is 3 channel boards (wait till I confirm that the design works) start with 5 or 12 volts, (your decision) and see how things go.

As far as 5 or 12 volts for 1 led.
5 volts can be slightly more efficient but, will it always be one led, because you can't easily change it.
If you go 5 volts you may have a noisy supply to the micro, this may or may not be a problem for the Current sensing on the Attiny.

If you go 5 volts you don't need the step up bc847 and it's two resistors. But you do need a different, logic level FET, just like AHellene's circuit.
5v you can use a smaller inductor.
I would use 12 volts but there could be a case for 5v and event a case for 7 volts.

If you want to use my circuit with 12v
just use a different TVS (12v operating voltage).
and remove everything including C3 to L2 reading left to right on the schematic.
Jumper the 24 volt rail to the 12volt rail.

If you want to use my circuit with 5 volts.
just use a different TVS (5v operating voltage).
and remove everything including C3 to U1 reading left to right on the schematic.
Jumper the 24 volt rail to the 12volt and the 5 volt rail.
you don't need the 3 x step up bc847 and short r13 to r15 and open circuit r16 to r18
It gets a bit harder as you may need a clean supply for the micro. I don't know.
Personally I wouldn't bother. It probably would be ok, but I think 12v will give you what you need.

Do you think this side of the circuit can be powered practically off the netduino

No the netduino can only source less than 1 amp.
I would power the netduino from my 12v supply. Maybe via a resistor to just take away a bit of the heat.

Also one of the resistors is marked as a bit wide, is this the foot print or the value and does it matter?

That is a mistake, it was left there from some other current sense resistor that I had considered, please disregard.

ps. You probably don't want to populate r28,r29, r30, I just put the footprints in for emergencies. I think 100mOhms if the lowest we could go anyway.
Also you don't need R12, this is also a contingency footprint.

Perhaps even provide a jumper option, where by you can select 5v or 12v and swap out the power supply accordingly?

You will loose very little running 1 led at 12v vs 1 led at 5. Only really in the higher series resistance of the inductor because you need a bigger inductor.
Just run at 12v.

How many ma are your running your Crees at in this circuit?

Steff shield is currently running 3 channels of 7 leds at 24 volts and at about 500mA. (XTE warm white) No heating problems on the shield and very little heat sink on the leds.
I will do 7 leds as well with my 24 volt prototype.
I want to move to 24 - 48. but will probably have to settle on a 24-36v version and 36-48v version, the black regulator doesn't have a wide input range. I just need to change a resistor value to switch between the two variations.

One thing that will work for you is the input circuitry on the Dimmer channels, you should be able to put your square wave straight in.
The input filters use 10k and 0.1uF which gives 166 Hz. If you can give it a pwm above 15KHz then your filtering is done.

BOM is corrected, thanks for finding the errors.

Attached Files

•  Steff2 BOM.zip   4.01KB   2 downloads

[mcinnes01]

Hi Magpie, I have gone through the BOM based on your suggestions, highlighting what I think is not required in red and what needs substituting for a different part in yellow. Please can you confirm that I haven't made any mistakes? I am going for the lower voltage of 5v as it requires less parts for my first test board and will probably be the mosted widly used for my aquarium lighting. I was also thinking once I have in dividual drivers made I may also adopt some more efficient "master" drivers that are used for standard running as well. I.e. for the effects I have my 10 driver boards with 30 channels, but then for the standard constant lighting I could make a couple of additional drivers that have longer chains of LEDs say 10 LEDs and these could be used for the constant lighting where LEDs aren't required to be controlled individually for example. Just a thought for the future, but I need to get a working example up first. For the 5v version, you mentioned I need a smaller inductor, can you recommend any that would be good for the job? Or will either of the ones I all ready have do the trick which seem to be 100uh and 330uh? You also said I need a different TVS diode, what would you recommend for this? PS I am probably going to order from Mouser in the UK. I guess the current sense will change in value right? Do you have the equation for 700ma from a 5v input? Finally the parts for the dimmer channels, are these already on the BOM and do the values still stand for 5v? Have you recieved your boards yet and got one soldered up? Thanks again, Andy

Attached Files

•  Steff2 BOM.zip   9.78KB   1 downloads

[Magpie]

Hi

Please can you confirm that I haven't made any mistakes?

I made some changes, added to new column that flags the changes.

For the 5v version, you mentioned I need a smaller inductor, can you recommend any that would be good for the job? Or will either of the ones I all ready have do the trick which seem to be 100uh and 330uh?

I left the inductors at 100u you can probably go smaller as well, probably down to around 10u. So many variables to choose these. 100 will be fine if you have them but say 33u might be better, but only marginally.

You also said I need a different TVS diode, what would you recommend for this? PS I am probably going to order from Mouser in the UK.

Look for operating voltage of 5v, but since you are providing a regulated low noise supply off board, the only thing this will do is protect against reverse polarity.
Also bear in mind that you need to provide the regulated low noise supply off board because this is what the 12->5v part of the supply was doing.

I guess the current sense will change in value right? Do you have the equation for 700ma from a 5v input?

No the sense resistor is about right, it will be ridiculously efficient but may be prone to noise.
You may want to try 200mOhms. I tried to layout my board inputs as "kelvin" inputs. Unless you do this well your current sense inputs will be prone to noise.
Any prototypes you may want to use up to 500mOhms.

Calcs: 100mOhms at around 700mA the current sense should read .7 x .1 = 0.07 volts at full load.
We are not getting all that 700ma through the sense resistor so say we get 500mA. ( Some goes through the Shottky). = 0.05v
then we multiply by 32 in the internal gain stage = 1.6 volts. our full scale may be 3.3 volts so we get a reading of 500/1024 at full current.

Finally the parts for the dimmer channels, are these already on the BOM and do the values still stand for 5v?

Your pwm outputs should feed straight in to these as long as they are 5v full scale. Dont connect the 5v but connect the rest.

Have you recieved your boards yet and got one soldered up?

Apparently they are in transit.
I have the parts from Digikey. The murata inductors look a mess, they must've been made by the apprentice. The last ones looked great.
I have also got some really fine prismatic diffusing glass on order, it breaks up the leds nicely. The plastic ones are good too but they look shit when they are turned off.

Good luck

Attached Files

•  Steff2 BOM revised for 5v.zip   4.88KB   1 downloads