OK i need help. not a noob but not an electrical engineer either. I’m looking for a solution for the limitations of ws2812 serial pixel trip length limitations and corresponding suffering refresh rate.
i’ve worked a lot with FastLED on arduino for smaller animated costume projects a while ago but recently got excited when the wife said I have permission to do 4-wall cove lighting for a room in our house… roughly 80 feet or 24 meters of pixels perimetering the ceiling of the room
I ordered a bunch of 5m reals of my usual ws2812b strips 60/m then i started seeing posts about linear refresh rate drop as lengths increase. I intend to reuse my very fluid animations from costume projects in this room so less than 30 fps is not going to look too well
So after hours of searching this forum I am now at 3 options:
A. toss these dense strips and order 30pixels/m to only double my refresh rate
B. buy insanely more expensive dotstars strips which dont really have a length/refreshrate limit
C. use some sort of parallel output to divide the long array
(or d. …not gonna happen) multiple sync’d controllers
Obviously I would love to have parallel outputs to divide my long string but parallel is not the nature of my little arduino. What hardware do I need thats FastLED compatible and can output in parallel.
I keep seeing references to the Octo but my understanding is that involves a new library and possibly a ground-up rebuild of my code
Also ESP. Been a while since I’ve coded with FastLED but no idea what that is or how it works with FastLED
I would go for a Teensy 3.2 AND the OCTOWS2811 adaptor that just plugs right on the Teensy. That will give you a huge (8X) boost to the available FPS.
24 strips X 60 Leds = 1440 LEDs.
1440 LEDs X 30 uSec = 43 mSec = about 23 FPS
With the OCTO, you will get more like 160 FPS
Yes that implies adding the OCTOWS2811 library but that is very easy import into the Arduino environment. You will only require very minor changes to any existing code, definitely no ground-up rebuilds !!
Your main problem will be more how to deal with limiting the voltage drop on so many LEDs / strips. You will need to be very very careful in planning the power distribution. Use the heaviest gage power wires you can and try to have the shortest possible lengths between strips and the PSU (s). You will most definitely have to inject power between strips.
APA102 (aka “Dotstar”) does indeed have a length/speed limit. Many people mistakenly believe APA102 is technically superior, and indeed they do offer a different set of trade-offs, which Adafruit in particular has promoted. The big problem is how APA102s “regenerate” the clock & data signals. It’s akin to repeatedly making an analog copy of a copy of a copy, like with a photocopier or analog cassette tape. As you use a longer length, the clock signal becomes more distorted. Here’s test results I published recently to show this problem. https://www.pjrc.com/why-apa102-leds-have-trouble-at-24-mhz/
@Gibbedy_G Yes 5v strips and i just started doing some math. You are not kidding when you say doing this neatly will be an issue. without software throttling its a theoretical max current of 86 amps wow. lots and lots of heavy gauge power injection wires
@Dave_Morris Having played with ws2812 strips for a while, I found that if you set them all to full brightness white, you draw about 45 ma per LED. In your case that would be 1440 X 45 ma = 65 Amps. I would still suggest to go for 80 Amps total of PSU(s).
I would suggest and it may be practical to go for 4 separate PSUs of 20 Amps each. Only the GND wiring needs to be common in all the strips.
@Dave_Morris Because you’ve already bought the strips, and the location your putting them, at this point I would be running a high powered 24VDC supply to allow you to run much smaller cable, with multiple cheap 5V 10A buck converters you can get off ebay.
going 5V supply the gauge you will need for reasonable voltage drop will be thicker than your strips.
If your cables/power supplys can’t be easily hidden in the roof or something and you don’t mind buying more strips I would say buy 30l/m 12Vdc strips. You will only need something like 15-20A supply, and you’ll get away with power injected at both ends.
The downside is lower resolution as its 3 leds per ws2811 chip so really 10 controllable lights per m.
I appreciate everyones input you guys are awesome. Ok after much consideration on powering so many low voltage LEDs and the resulting high amperage, I have adapted my design.
30 LEDs/m instead of 60/m. half current double frame rate, half resolution =(
Single 300W 5V power supply with 3 output screw terminals and adjustable voltage. Possiblly bump voltage up to 5.5 or even 6.0 to reduce amperage 10-20% if WS2812b tolerate it
3 x 14 gauge distribution wire runs for power injection every 150 LEDs
Let me know what you think…wire gauge, DC injection frequency, etc.
Also, It is not easy to give a clear OK for the wire gage. If your wire length from PSU to strip is very long, you may still get an unacceptable voltage drop.
I would test all the strips with the exact same wiring length on a bench and check for voltage drops and steady operation / brightness everywhere before trying to mount this somewhat permanently.
Here’s a link to a tool that has helped me to figure out wire sizes on various large LED projects:
@PaulStoffregen I don’t know about ws2812. There is no extra heat dissipated in the led, only the ws2811 chip (although I think you meant that). As I mentioned I’m talking about those strips wired with 3 leds/ws2811 chip. You can do the math and measure the results. Ignoring efficiency difference, which isn’t allot when driving 3x leds per chip like these strips do, 50mA at 12VDC gets you 3 leds lit up at full brightness. Compared to 150mA at 5vdc gets you 3 leds lit up at full brightness. The advantage of running smaller cable gauge/ less power connections requred have to be weighed up against lower resolution of 10l/m.
@JP_Roy You are correct if you are talking about 1 ws2811 chip per led. I have yet to see a 12VDC ws2811 strip like this. Again maybe it’s different for ws2812 as I haven’t looked into them.
@JP_Roy Regarding voltage drop and wire gauge it can be calculated accurately by testing/deciding on acceptable voltage drop for the leds your using, with an ohm meter and some math. 12V strips are very tolerant of voltage drop but at some point I imagine you fry the ws2811 chip.
@Gibbedy_G The WS2812 is a WS2811 chip integrated with a RGB LED in a 5050 package. It would behave identically with regards to an increase/adjustment to 5.5V or 6V of the output of the 5V supply that Dave intends to use.
Paul is mostly right in his description of the constant current nature of the RGB LED but the LEDs will still draw slightly more current when a higher voltage is applied. Increased voltage and increased current through an LED or any component implies more power and more heat dissipation. The power demands of the ws2811 chip itself, integrated or not is insignificant compared to the RGB LED.
I agree with you about using 12V style strips and the reduced overall current for the same power demand as opposed to a 5V style but again that is not what Dave intends to use.
