hi all! I'm dario,

hi all! I’m dario, an arduino hobbist from italy

I need some info before start using fastled libs with an apa102 60/m strip

first of all, how many leds can i drive? i tried neopixel, and I can drive about 700 leds, how about fastled?

thanks in advance!

What board are you planning on using? RAM plays a big factor with the number of LEDs that can be used as well as processor speed to be able to drive the LEDs with a high enough FPS to look good.

arduino uno or arduino mega are ok? maybe arduino mega is better

@Dario_Gavezotti Here’s some stuff to think about in general even though this was not specific to APA102.

How many LEDs are you wanting to drive?

@marmil thanks :slight_smile:
@Brian_Lewis I was asked for a feasibility study for a 1m (60 led) wave slowly moving along a 75m (4500 led!) strip. slowly means switching off the last led and off the next every 16ms so the wave will move forward about 1m/s.

This is a somewhat complex question - as there’s a bunch of pieces that dictate “how many leds” you can drive. The first is going to be memory - you want to drive 4500 leds, and each led takes 3 bytes of memory, so you need something with at least 13.5k - more likely 16kb to give yourself some reasonable headroom. That removes all the AVR based platforms from your options and you should look at something like a teensy 3.2 or such.

The other piece comes down to how long it takes to write the data. If you can drive APA102’s at 24Mhz then it takes 1.3µs to write out the data for a single led - or just under 6ms to write out 4500 leds worth of data. However - there are problems reported with many APA102 strips not being able to handle high data rates the longer the strip is (something to do with the strip itself, not the apa102). So, if you have to push the data rate down to 12Mhz, then you’re looking at 12ms to write out 4500 leds worth of data. If you have to go down to 1Mhz then you’re looking at 144ms to write a frame.

You’re going to have to do some experimenting to see what driving a single 75m strip of APA102 leds. You will also need to inject power at multiple points (rough rule of thumb is every 100-200 leds). A ‘dark’ apa102 chip draws 0.9ma of power - so you’ll be pulling 4A of power down even without turning any leds on. If you run into problems with getting a usable data rate with a single 75m apa102 strip you may need to have controllers every 10 meters or so (depending on what you find out in your tests of length vs data rate).

@Daniel_Garcia thank you for your clear explication.
how about using an arduino due (96 kb) or arduino 101 (24 kb) board?
and how about splitting the 75m strip in 15m sections, each connected to a different arduino port? (I suppose that this doesn’t makes any sense, it’s true?)
it would be better to control each section with a feather m0? the advantage is that I can synchronize via udp the five m0…

If you’re going to do wifi syncing stuff - I know for a fact this can be done with the esp8266 boards - as i’ve done it multiple times now - I believe the feather m0 should work (it’s basically an arduino zero). The arduino due would be an option, however the arduino 101 is not supported by FastLED.