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Author Topic: Building an addressable LED strand with WS2801 (custom pcb)  (Read 8476 times)
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Just ordered 10 of each part to play with, all smd so I guess im gonna have to jump straight into the fiddly work
KirAsh, did you do the board layout yourself? I would love to see it if you have any photos or layout diagrams, or if you will help me design one I can pay you?
Again thanks for all the help here!

Jules
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I don't have any of the boards on hand ... at least, if I do, they're buried in a box somewhere.  But, this is what the last iteration looked like graphically.  The one with only three LEDs is the default configuration.  And the other is if one decides to populate all six pads.  The double row of pads on either side is for an SMD header so I can daisy chain as many as I want by using a six wire ribbon cable: 2x VCC, 2x GND, SCK, and MOSI.

If you need help creating a board, let me know.


* PXL Top.png (102.74 KB, 1536x978 - viewed 42 times.)

* PXL Bottom.png (120.74 KB, 1536x978 - viewed 33 times.)

* PXL Bottom 2.png (110.97 KB, 1536x978 - viewed 30 times.)
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Hi Kirash,

It looks like you have built almost the exact board I am after! I have had a play around with the leds and they seem perfect for me, I also have the other components I need but they are all smd so they are pretty tiny.
I have decided that the best option for me will be 6 leds per module (quite alot I know), It will be 3 leds per channel. I also wanted to have headers like on the board you made, though I would use a second board with the plugs and wires soldered on so that I could fix the 'wired' boards to something permanently but be able to remove the led boards easily.
 
I would love some help designing the layout, to be honest I feel a bit out of my depth here, I have had no previous experience so it looks like I would have to learn entire new software packages as well as everything else to make a decent pcb layout.
It looks like the board you made is very very similar to what I am after so maybe only small changes would need to be made?
If you do have any free time to help me here I would really appreciate it! If you want some cash just let me know and we can discuss this, I'm just desperate to make this work!
http://uk.farnell.com/ stock loads of parts and deliver very quickly but when looking at the parts I was not quite sure exactly how to pick the right ones as there are so many variations, If you could suggest which parts to get for the pcb this would also be a huge help!

I really appreciate that your taking the time to help me here
Best,

Jules
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You're better off with 2 per channel.  After all, the WS2801 has 3 channels.  The modules I made have four mounting holes on the corners, so I'm able to mount them on something.  The header is on the back and the ribbon cable runs from module to module, forming one long string.  If one of them failed, I just remove the ribbon cable, detach the board and put another in its place.  In one installation I hung them literally from the ribbon cable itself and then ran fishing line through the holes but that was only to align all of them nice and straight.  Plenty of possibilities.

The first question I have is: what's your timeline?
Second question: what's your preference in components, through hole or SMD?

I choose SMD because it makes for a nice clean surface on the side where the LEDs are, meaning there's nothing sticking out on that side.  However, if you are not comfortable with small SMD parts, then we'll have to design a through hole board for you.  Might be worth putting all the components on the same side just so you're only soldering on the one side and not both.

If you choose SMD, you'll need to know how to either solder them by hand, or something like a skillet reflow method (which is what I do) and you'll need a hot air unit to do the other side of the board.  Basically what I do is a skillet reflow method on the LEDs, then use hot air to reflow the components on the other side.

I could've done everything on one side, including the headers, but that's just ugly to have the visible aspect of a board get cluttered with other components.  Having it double sides makes for a very clean face where the LEDs are.
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The reason I say 2 channels is because I will need equal illumination on both of the channels, and as much illumination per channel. If three per channel is a problem I could probably reduce it to 2 x 2 but at the minute I don't really have a use for the 3rd channel, I can always leave the traces blank like in one of your images
The mounting holes although very useful may not be the ideal solution for my uses because the modules may be removed and replaced quite frequently but without disturbing the cable arrangement,
Again it something I can work with and I see no reason to change your current design of the board.

If by timeline you mean how long can I wait for this? I have no dates set in stone but I am trying to get things on the move because the printing alone will take about 2 weeks (economy) and that's from when I have something to send them, basically there is no real time limit on this within reason. There is a big recession here in the u.k so it if more time vs more money, time will win.

Smd all the way! I want these to be small and neat and I am more than happy to work with smd, I will be using the skillet (or toaster) reflow method, then heat-gun the other side as you mentioned, I may get a solder paste stencil cut when I get the pcbs cut.
Two sided pcb is better for me as well.

One other point to note, Ideally the layout would be as follows: (in the board layout you uploaded) channel one indicated by where the leds are, channel 2 indicated by where the empty spaces are...  if that makes any sense..
Thanks,

Jules
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Ok, the reason I suggested spreading the LEDs across all three channels is to balance the IC itself.  Not that you can't only use one or two out of all three, but component-wise, you may as well populate all three and use them when needed, as opposed to only populating two channels only to find out you need a third later and having to re-heat the board to add the remaining components.

My personal choice would be to add two LEDs per channel, which will give you a 33.3% intensity with each channel lit.  You can turn the light up and only have 1/3 of the LEDs lit (one channel on all the ICs).  Push a button and turn on the next set for a 2/3 coverage, or turn it full blast by having all three channels lit.  It's a nice way to control the light in (3) steps.  Of course you can add more steps in the software by using PWM on each channel.  That particular board uses RGB and all three channels, regardless of how many LEDs are on the board, 3 or 6.  Kinda obvious why ...

In the end, it's your choice though, but having 3 LEDs on two channels isn't that much different than 2 LEDs on three channels other than the amount of light you'll get from having 2, 3, 4, or 6 LEDs lit at any given time.
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I see you point and I agree that would be a better solution in most cases but I will be filtering each channel so I can really mix the channels to increase intensity.
My choice to use 3 leds was to avoid realizing at a later stage that 2 leds did not create sufficient illumination, In all honesty I think two would be enough but I would rather be safe than sorry.
My priority is really that the the light output is high, and that I have 2 channels that are neatly balanced (location wise), but I guess things are a bit flexible.
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can't really mix*
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Can a bunch of WS2801 modules run WITH an ethernet shield? What if i skip the whole ethernet option and just use a WiFi shield? Will that clash too? BTW, I got my ws2801 modules from http://www.ledlightinghut.com/ws2801-square-4-led-pixel-module.html
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They can run with anything you want.
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Hi Kirash, I'm sure (assuming this would even work) that there is a far neater way to do this but I have had a quick go at laying out the pcb:

this is just a quick sketch I did in rhino, I know it is not very neat but it allows the channels to be laid out as I require.
I would make a few tweaks to the board to tidy up the whole thing, and I would also like to move the bottom 3 vias to the right a bit (and the corresponding components on the other side the to match.
I would also make the traces a bit thicker than in this sketch, and the 'contacts' for the leds would be a lot wider. I would also look into led heat dissipation.
basically this is just a very quick sketch but can you see any major problems with the layout? (by the way, the red arrows correspond to the cathodes)
from the images you uploaded I can't really figure out what all of the traces and vias are doing because the components are blocking parts so I made a few guesses...
What are your thoughts?
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Forgot to mention that I would also sort out the very close traces near the bottom left of the top right led...
Best

Jules
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That means nothing to be honest.  It doesn't show where the IC and other components go, doesn't show what pin goes where.  You have one single trace that goes to all the LEDs in a spiral fashion.  No clue what that is.  No way to know if it's going to the IC or what.  There is no indication of a dual channel setup either.  rhino isn't a PCB schematic and layout program (but you knew that already.)  Wrong tool for the job.
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I understand that, It was not a pcb blueprint, just a suggestion.
It was simply an example based on the led side of the png you uploaded.
I can see how it looks confusing, especially the spiral trace, again it was an adaptation of your layout. (for the record the s shaped section at the top between the two vias is carrying the voltage)
To be honest I am a CG artist/photographer, not an electrician or even a hobbyist, I have tried for months to make this work including hiring a freelancer but nothing has worked for me (as you can see)
I am so grateful that you have been willing to help me on this because I am not really capable of doing this by myself, but I was not sure if you were going to continue helping me.
The changes to the board seem so simple yet they are in a language I don't speak, will you help me make this work?
Thanks

Jules
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No worries.  Blue prints are better than no prints.  Work on the schematic part, don't bother with the PCB as that will fall into place when the schematic is correct.  So you need the exact specs on the LEDs you plan to use as far as voltage drop and current goes.  How many total, and how you wish to control them.

Having 3 per channel, using two channels only means you can have either 3 or 6 on at any given time.  You will be able to control each channel which in turn controls the 3 LEDs connected to that channel.  So you could dim one set while leaving the other on.  This isn't any different from having 2 LEDs per channel, using all three channels to turn on/off/dim the LEDs.  It's a matter of personal preference and how much control you want.  Having two channels with the 6 LEDs in a Star of David configuration (where each major triangle is a channel) works well as it produces light across the whole board as opposed to only one side.  See attached mock up.


* star.jpg (10.25 KB, 177x177 - viewed 15 times.)
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