I know that the WS28xx strips have only a data pin and the APA strips have both data and clock pins. I’ve done all my projects so far with WS strips because hey, one less wire to worry about! But I was just looking at Jesus Vicente’s POV project and noticed he was using APA strips and mentions using a hall sensor - I’m guessing to get the timing of the LEDs sync’d with the rotation. That made me wonder if that kind of application requires a strip with clock pin. Is there a time where one is better to use than the other?
The reason people use APA102 instead of WS2812 for POV projects is because the APA102/SK9822 pixels have a faster PWM and refresh rate. Although im pretty sure the new SK6812(a clone of the ws2812) has a fast enough PWM for POV)
@Leon_Yuhanov Thanks, Leon. Does this also mean that APA strips would be better for a levitating water or other stroboscope project?
@Karl_Tinsley Better yes (but that is because they are a more advanced system) but necessary I’m not sure.
-WS2812 has a PWM of 400Hz
-SK6812 has a PWM of 1.2KHz
-APA102 has a PWM of 1.2Khz
-SK9822 has a PWM of 1.2Khz
What that means is that if you have a solid colour, lets say RED on all of these pixels, they would flicker at that rate.
The next consideration is each models REFRESH/DRIVE rate. That is the Speed at which you can update data to them.
-WS2812 driven at 800khz (800kpbs)
-SK6812 driven at 800khz (800kpbs)
-APA102 driven at 20Mhz (20mbps)
-SK9822 driven at 30Mhz (30mbps)
@Leon_Yuhanov Okay, good info. I think I’ll order some APA102 for my stroboscope projects. Thanks again!
In addition, (as I recall) FastLED disables interrupts when using WS2812’s, however they’re enabled with the APA102’s. As a result, it’s much easier to add peripherals such as IR with the latter.
The APA102 PWM cycle rate is closer to 20khz https://cpldcpu.com/2014/08/27/apa102/ - so nearly 50 times the rate of WS2812.
Leon’s explanation is spot-on. For my own persistence of vision project, I initially used WS2812Bs and found that they caused ALOT of flickering when I tried to strobe them at 80 Hz. After getting some great explanations from Daniel back then, I swapped to APA102Cs and they’ve been flawless since!
@Stephen_Co Thanks Stephen! What are you using the control the strobing LEDs? Is a nano or pro mini fast enough, or do I need a teensy?
@Karl_Tinsley , I’m using a nano, but I was actually thinking of including the nano on the PCB already along with all required components (regulators, headers, FETs). Did you prefer a bare PCB and you can tinker/solder with it yourself?
I’ve done most of my projects so far with nanos. They are already soldered up, except for the headers, which I usually leave off, because I usually only need 5v, gnd, and a digital pin for the LEDs. Occasionally one other digital pin for a button. I don’t mind soldering, but I think I prefer the board all soldered up in advance.
Ah, then yeah, the nano is totally fine (more than fine actually) for doing this. I find the only limitation is running out of IO pins per “timer” group (there’s only 3 timer groups).
I primarily work with Nano’s and buy them by the 10 pack. Great little device.