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Author Topic: Building an addressable LED strand with WS2801 (custom pcb)  (Read 6926 times)
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Great, so I want to use 6 leds in total per board. I would like 3 leds per channel, so two channels.. just to note that I will never, or very rarely use the 2 channels simultaneously, just flick between the two, but I would like to be able to dim each channel individually.
the Star of David configuration is perfect, that's exactly what I'm after!

The LEDs are as follows: Avago - ASMT-QWBG-NFHDE  150mA, 3.4v (typical) 3.6 (Max)
I ordered a few of these and they seem perfect.

In total I would like to have 90 complete modules daisy-chained together and be able to turn on/off or dim either of the two channels on each module individually, I was going to run them from a 12v power supply.
Again, Thanks

Jules
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And final module size?
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Similar size to yours by the looks of it, around 30mm x 30mm. The leds in particular are really tiny so I don't think that will be a problem (3.2mm x 3.5mm to be exact).
The other thing is the header(s), I had trouble figuring out if what I was looking at was suitable on farnell, maybe its best to go for the same ones you used.
 
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I just used regular rectangle headers, SMD mounted.  Something like this:

http://uk.farnell.com/samtec/tsm-104-01-s-tm/header-2-54mm-smt-12way/dp/2044053

I specifically used a 2x6 header for several reasons.  Two rows so I have a good grip on the board and less chances of ripping it off.  And 6 pins so I can have 2x VCC, 1x DATA, 1x CLK, and 2x GND.  Duplicate it for the second row.

Then I used ribbon cable plugs to connect to the boards, like these:

http://uk.farnell.com/amphenol/t812112a100ceu/socket-idc-2-54mm-12way/dp/2215233
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Ok they look good, they are not £3 each are they?! that would set me back more than the 540 leds! does it mean for 5?
2 rows makes sense to me as well...
What would be the next step then? build a schematic?
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Eh, that specific one seems a bit high yes.  There are others, just search for board headers, rectangle, 2.54mm pitch, 12 pins, 2 rows, SMD mount.
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I might just try to find some bulk packs from china, might save me alot of money in the end...
So whats next? Is it important to know exactly what components to use before making the schematic?
btw, I have just got my 'led pixels' http://learn.adafruit.com/36mm-led-pixels/overview so I can finally start playing around with the code for the ws2801  smiley
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No, the schematic is simply symbols.  Actual parts (as far as whether it's a through hole or SMD, and what size) is mainly done on the board side.  So either you figure out what parts you want to use and tell me, or I build the board and tell you what parts to get (this is what I normally do.)

Code for WS2801 is easy.  Download FastSPI and run the testleds sketch (after adding a setDataRate(2) delay before the .init() call.)
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Ok,
When you say build the board, do you mean 'theoretically', or mean to actually build one?
I'm sure you would be better at picking the parts than me so maybe that's a better solution, the only parts I need for sure are the leds, apart from that I guess reasonably cheap smd parts are what I'm after,
not so fussed about the size... I have played around with some 0603 resistors, I can work with them no problem.
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Code for WS2801 is easy.  Download FastSPI and run the testleds sketch (after adding a setDataRate(2) delay before the .init() call.)
will do, thanks
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No, I mean building one in Eagle.  Ready to go to a fab house of your choice.
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Ok, perfect!
I will be using the avago leds and the same header dimensions you used, all smd parts, and 12v input. Apart from that I guess the layout can dictate the rest.
Just let me know what else you need
Thanks

Jules
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Aight.  I'll work on it over the weekend.  I need to re-create the Avago LED in Eagle first and go from there.  Different pads and dimensions.  Do you have a preference on size for the other components?  For example, do you prefer 0805 resistors or can you work with 0402?
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Amazing! thanks.
I guess I can work with 0403 but I don't really have a preference, whatever you would do really, considering cost as well.
This is really exciting for me, thanks

Jules
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Cost difference on one specific one:
0402: £0.011
0603: £0.007
0805: £0.024

Depending on the actual resistor needed, I may or may not be able to get the size I want to use and will have to use a different one.  For example, sometimes I can't get a 10K in 0402 size and have to use 0603.  And I'm trying to stick with Farnell since you said you're in the UK.
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That's fine, if there's so little in it I am not so concerned, equally, I am not going to mass produce this so I am not so worried about variations in size.
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