Has anyone worked with the 12v strings? What are the benefits/drawbacks? Why 12v?
I have some that I plan on using soon. Actually bought them on accident, but its ok. One drawback is that if you are using a battery as a power source: 1. It needs to be 12V, and 2. Your controller needs to also be able to accept 12V or you need to buck the 12v down to 5V or 3.3V.
I often use 12-volt setups. Two main reasons I do it are:
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When power is coming from a 12-volt native source, e.g. car battery, solar panels, etc.
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When I want to power longer runs of LEDs before you needing to inject more power. For example, I have a 20 meter (65 foot) long string of 200 WS2811 “pixel nodes” that’s happily powered from just one end. You can’t really do that with 5v strips, due to voltage drop, etc.
I also use 5-volt setups, when I have 60 or fewer pixels, or if I want to power the whole thing from USB. There’s also the consideration that @Adam_Wright mentioned above: if your microcontroller can’t handle 12-volt power, you’ll need to step it down.
One other drawback I can think of is that I believe that 12-volt strings are somewhat less power efficient; the 5v voltage regulators that are present at every(!) pixel sap a small amount of current themselves.
What project do you have in mind?
Almost all of my projects are designed for cars, but I use 12v to 5v step down modules rather than 12v strips or halos. The modules also smooth out any spikes in the car power supply which can prove fatal for LEDs 
Mark
Where to you get your 12v strips from?
I have more high amperage 12v supplies than 5v, and higher voltage is slightly less loss than 5v over wires.
But, the 12v strips I’ve seen are addressable in 3 pixel chunks, not as individual ones. If that hasn’t changed, it’s something to be aware of.
Yep. That’s a bit dated I think.
Check out TM1809 strips (12v, protocol supported by FastLED), and searching Ray Wu’s store shows a pretty wide variety of 12v pixel strings as well. All individually addressable pixels.
And then there’s this beast…
5m DC12V WS2811 450LEDs (30pixes/m) WHITE PCB led digital strip;IP66;waterproof in silicon tube
12v, three 5050 RGB units / “pixel”, but arranged in clusters on an extra-wide PCB strip.
Can draw over 20 amps at 12v.
Eye protection not included.
I purchased two 50 pixel bullet style strings. This is the first time I have played with addressable LEDs and I can see how the power issues play into this. Even with just 100 pixels I had to add power at either mid way or at the end of the string to get consistent brightness using a single 10amp supply. I have ordered my first 12v strip to do some testing. Thank you all.
From a purely electrical standpoint, 12v is easier.
Less voltage drop
More larger power supplies
But what I’ve noticed is that 12v strips are only addressable every 3 LEDs.
On a bigger display it isn’t a big deal, but for desktop sized stuff it might be
These TM1809 strings are 12v and single-pixel addressable. You can only cut it every three pixels, but you can address and control each pixel independently.
FastLED supports the TM1809 chipset.
I’ve built two separate 300-pixel 12-volt projects with TM1809s. Works fine; speed is like WS2811/WS2812.
(Fun side fact - FastLED supported the TM1809 before the WS2811 
Holy shit, @Mark_Kriegsman ! I wish they’d been available when I was doing a certain Dutch Project!
Also a looks like I need to spend some time on LEDstimator :-/
My first 12v string arrived.
Can anyone suggest how to wire these with a Arduino? I guess I expected 2 connections for driving, but all I have is 12v, DO, and GND.
Finding posts similar to these:
I guess I was expecting wiring for both clock and data.
“5M Waterproof WS2811 IC 5050RGB Dream Color 30LED/M DC12V Pixel Strip Black PCB”
The WS2811 IC portion there means that they are based on the WS2811 - which is a 3 wire led chipset. (Also note that it is 3 physical leds per “pixel”)
@Robert_Atkins as far as I remember, the TM1809’s were around before the WS28xx’s. I had TM1809’s before I had WS28xx leds.
So the DO goes to the data pin and it is safe to connect the GND to the arduino GND (using trinket pro)? Obviously I power the arduino with a separate 5v supply.
No - DO is “Data Out” - go to the other end of the strip - you want DI - which is “Data In”. You will also want to connect the ground on your leds to your 12v power supply, in addition to the ground on the arduino.
Thank you. Turns out my power supply is way too weak. New one arrives Monday.