Building an addressable LED strand with WS2801 (custom pcb)

The one thing to keep in mind when creating multiple LED "pixels", is heat dissipation from the LEDs. Normally I create boards that will have vias on the thermal pad going to the other side of the board where I can then vent the heat, or use a fan.

Amazing, Thanks for the info.
I'm slowly starting to understand what is going on here, I think I will benefit from a bit more study in this area though, might invest in a book.
guess the next thing to do is get some of these parts and see what I can make something happen :slight_smile:
But let me get this right, using this circuit (with changes to the resistors) would 12v be suitable? (assuming R7 is 2k)
And I can't quite figure out how the zener does anything in that location, that's really boggling my mind! is the ground location important?
thanks

Jules

I am going to print some pcbs and reflow solder them so I will make use of the 'isolated heat pad' they mention, thanks for pointing that out.
They probably wont stay on for more than a few seconds at a time so hopefully I wont need a fan, I will certainly look into draining a bit of that heat away though, thanks

bograt:
guess the next thing to do is get some of these parts and see what I can make something happen :slight_smile:

Best way to play.

bograt:
But let me get this right, using this circuit (with changes to the resistors) would 12v be suitable? (assuming R7 is 2k)

Yup. The only resistors you need to change are R1, R2, and R3.

bograt:
And I can't quite figure out how the zener does anything in that location, that's really boggling my mind! is the ground location important?

Ground is ground, doesn't matter. Just pour yourself a ground layer and tie them all together.

Here's a different view ... Again, I'm using 20mA per channel LEDs. So change the resistor values on R1, R2, and R3. And the part listing is for 0603 parts. The LEDs are 5050 RGB LEDs which I have several hundreds of so they're not listed.

I can easily make this into a board, however, I've never done a DIY board ... I've always sent them off to a fabrication house. Doing it by hand means you'll probably need thicker traces and what not. This particular schematic is on a board that's around 30mm^2 ... I forgot the exact dimensions.

This information is absolutely priceless to me you know, I really owe you for this, I will have to give you some cash at some stage.
I was planning on getting the pcb's printed here in London along with a laser-cut reflow stencil, and then trying my luck at assembling them to cut costs. the quotes I got for assembly seemed a bit steep for the work...
I know things will be small, I have very steady hands a good eyes so I though I would try my luck, also I was hoping that using a stencil and oven would mean I could work smaller.
Out of interest did you get the schematic you uploaded made?

Yep, many times.

I just saw this on eBay - RGB LED with a built-in WS2811...!

You should be able to pack those quite close together :slight_smile:

Edit: I forgot the link: http://www.ebay.com/itm/160886742091

fungus:
I just saw this on eBay - RGB LED with a built-in WS2811...!

You should be able to pack those quite close together :slight_smile:

Yes, those are single LED per IC. We're talking multiple LEDs per single IC, which is also possible using the WS2801. eBay doesn't sell those.

Thanks for pointing that out fungus, just looked them up and although not suitable for my current needs, it looks like an interesting component.

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

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.

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

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.

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

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.

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.

can't really mix*

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 Best 35mm Square WS2801 Digital RGB LED Pixels

They can run with anything you want.