WS2812 + Octo + capacitor?

[BuffaloFan32]

I have been researching why I keep losing LEDs in my display and came across a tutorial from Adafruit where they recommend putting a capacitor between the + and - leads of the LED strip:



I noticed that the Octo has a capacitor in the schematic, so, is it still necessary to add one if you I am using an Octo adapter to control the LEDs? I also believe that the resistors that some people use in line with the LEDs are already built into the Octo.

In my setup, All my strips are wired to a bus bar for + and a seperate bus bar for -. Can I just put a capacictor between the bus bars instead of one on every strip?

 

[Eka]

The capacitors are there to absorb spikes generated during switching on and off of gates, LEDs, etc. Also a big bulk capacitor will absorb the bigger spike when you turn the string off. I have 100uF electrolytic plus .1uf ceramic caps at the ends of all the APA102 strings of LEDs I use. In reality the strings of LEDs really need decoupling caps for each LED or two, and I put a 0.1uf ceramic cap every 5 to 10 LEDs. They are generating little spikes every time they turn on and off. If you want the LED array to work in very cold temperatures, then use tantalum caps instead of electrolytic ones.

Mike over at EEVblog has a few YouTube videos on decoupling capacitors.
https://www.youtube.com/watch?v=BcJ6UdDx1vg
What they do for you visualized on an oscope.
https://www.youtube.com/watch?v=1xicZF9glH0

 

[defragster]

What they do for you visualized on an oscope.
https://www.youtube.com/watch?v=1xicZF9glH0

Without EE background watching this vid was interesting. One thing to know/generally understand to put a cap on each chip 'as directed' - the video shows how significant that can be.

 

[PaulStoffregen]

Most LED strips do have 0.1 uF capacitors between each LED.

Whether you need to add more capacitors is a good question. Adafruit's advice is based on the typical usage of their customers, which is either batteries or cheap wall-wart type power supplies which have long wires, and relatively small projects with 10 to 60 LEDs. When you have a long wire, or when a battery is nearly discharged, the impedance isn't low (or you can think of this as "weak" power). Adding a capacitor lowers the impedance for higher frequencies.

For a large LED project (big enough where OctoWS2811 makes sense), you really need very capable power supplies and they should be located close to the LEDs with fairly short wires. If you've followed that advice, then the power supplies have huge capacitors which give a very low impedance. Add more capacitors probably won't have any significant effect.

If you've used long power wires and they're not huge diameter wire, you'll probably have all sorts of problems. Adding capacitors might help. But for such a large project, it's unlikely to be enough.