I'm working on a project where I want to control a number of 30-LED (WS2812B) strips in parallel. At the moment, I'm using the GPIO18 PWM0 pin on a RaspberryPi (Model b Rev 2) to test my code on a small WS2812 strip, and that works fine, just using the power from the Pi. I’m using the library from https://github.com/jgarff/rpi_ws281x to drive the individual LEDs.
In my actual project I want 19, metre long (i.e. 30-LED) strips, and I want to animate them all in parallel. I'm only currently running them at about 10% brightness, but I'm wondering about how much power I need to be able to run this. At any point in time, there will only be about 15 LED's running per strip, and most of the time none at all (the animation will be triggered by a button and runs for about 5 seconds).
This is all for a costume, so I'm trying to work out how to wire this, and power this portably. My Pi, I think only has a single PWM pin, so that means I either need a newer Pi with more PWM pins, or I think I have to run all 19 strips with the data lines connected in serial (meaning more wiring, and distance for the data line).
Here is a rough diagram of how I think I need to wire it up.
(p.s. yes, I know the image only shows 18 strips)
Originally, I was hoping to power them all in parallel, and run (say) groups of 4 or 5 strips per PWM line (because I thought there were 4 on the Pi, not 1), but I'm no longer sure I can do that unless I have a Pi or other device that can drive multiple data lines.
Power
So if I understand correctly, I have 570 (LEDs) * 50mA (per LED) * 0.1 (brightness) = 2850mA which I think is 2.85A. Is this correct, and is it a reasonably accurate way to estimate the power I’d need?
If so, it seems to me that I need to connect all 19 strips in parallel to the power, and then drive their data lines from the Pi, or other device. By putting the strips in parallel for their power the amount of power required I think should be less.
Data
Even if I assume I can power the 19 strips, I’m still not sure about controlling them all via that single PWM line (GPIO18). The more I read, the more uncertain I am about the ability to drive separate strips without having to run the data-out from each strip to the data-in of the next one, which means (in my project), a length of wire between the strips (35cm at the outer edge in the image, and 6cm at the centre). So all up, to put the data of all 19 strips in serial like this, I’m looking at, I think, around 23 metres of data line, and that seems like a lot to me, making me worry that the data signal is going to degrade resulting in the animation not working consistently along the entire length of the data line.
The animation on each of the 19 strips is to be identical, and run at the same time. Is there a way to drive all 19 data lines in parallel, like have a single signal from the Pi/other device that controls each of the 19 separate strips as if they are a single strip?
If not, and there is a way to ensure that the 23 metres of data line is OK, then it's just going to be some tricky programming, but that, I do know how to do.
