[Noisebridge-discuss] NB Maker Faire table electronics question.

Torrie Fischer tdfischer at hackerbots.net
Mon Apr 13 16:23:02 UTC 2015


I don't have much familiarity with WS2812 strips yet, just LPD8806. Those are 
the kind that I've installed in the space. I'm totally out of free LPD8806s, 
having just recently assembled most of my rolls into two more skylighting 
cells.

Like Mitch said, you'll want to wire up your capacitors in parallel with your 
VCC/GND lines:


o--VCC-------o
       |
     +--- 1000uF
      ---
       |
o--GND-------o

Electricity doesn't flow through a capacitor. To use the water analogy, 
imagine the capacitor as a section of pipe with an elastic impermeable 
membrane in the middle. Electricity will push up against it resulting in the 
membrane storing energy. Once the source is cut off, the membrane starts 
pushing its stored energy back into the system.

Obligatory gif:

http://upload.wikimedia.org/wikipedia/commons/c/c1/CapacitorHydraulicAnalogyAnimation.gif

As a suggestion, you could just use a regular ATX PSU to power the whole 
system instead of two separate boxes. Yellow lines provide +12VDC and red 
provides +5VDC. they're usually very well regulated so you shouldn't need to 
worry too much about filter caps. There is a bin in the hack shelves full of 
PSUs just waiting to be repurposed for stuff like this :D

Looking at the physical layout a bit more, I don't think you'll be able to get 
an LED strip to lay flat and make those curves. You'll need to snip some short 
1 or 2 LED segments and make a segmented turn. Tedious work, but c'est la vie.

On Sunday, April 12, 2015 02:52:34 AM jarrod hicks wrote:
> Hello Noisebridge discussers
> 
> My name is Jarrod and I mostly do woodworking projects at NB. So I am very
> excited to finally be asking an electronics questions to the discussion
> list. This is in regards to the Maker Faire booth table we're building. I
> am new to LED/Arduino projects, but want to make sure I get a decent setup
> put together so others can take things further that I can.
> 
> First, I have drawn a PDF diagram of how I think the electrical system
> inside the table will go together. Here the location of it on the wiki:
> 
> noisebridge.net/images/1/1e/Noisebridge_Table_ElectricalDiagram_v1.pdf
> 
> 1. Does this power scheme make sense, is there a significantly better way?
> I plan on installing over 4 meters of 60/Meter WS2812B strips. My count is
> about 301 light sources (>5m). The documentation I have been reading makes
> it clear that 4m is the max that I can power as a single strip. Based on
> this I think I can separate the installation into 2 halves. To power theses
> strips I am thinking I can connect them both to a single 5v 20a power
> supply based on 301 lights x .06A = 18.06A at full white.
> 
> 2. Should I not use an Arduino Mega 2560 R3 to run this?  I am concerned
> that this has the headers installed, would this make the wiring difficult
> or unreliable?
> I read that the WS2812Bs will take up a fair about of the Arduino's memory
> and that the UNO or Pro Mini with 2k SRAM may not be enough to allow
> additional "libraries". This doesn't mean much to me yet, but the price
> difference isn't too bad and I would like for others to be able to make
> this LED installation do other things in the future, so unless there is a
> "deal breaker" I am not aware of I will stick with it.
> 
> 3. This table will be connected to a 120VAC outlet for power. With the 5V
> 20A LED power supply and the 12v Arduino power supply running, is there
> still a decent amount of electricity left over from a typical 120VAC power
> outlet to make it worth installing AC power outlets in the table?
> 
> I plan to buy parts very soon so any help is appreciated. Please let me
> know if clarification is needed.
> 
> Cheers.



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