Neopixel resistor 6v to 5v

I'm doing research into a project. What capacitor should I use with every bare ws2812b/ws2812 the schematic says "104" but it doesn't say what measurement. microFarads? picoFarads? nanoFarads? Anyone know?

https://cdn-shop.adafruit.com/datasheets/WS2812.pdf

It's 100 nF (10 x 10^4 pF).

I'm also trying to run the project from 6v (two 3v coin cells). The batteries in series have at most 500 mAh and the circuit might need to draw maybe 25 - 100 mAh. I used a calculator and it said I could use a 10 - 40ohm resistor. Can anyone with more knowledge double check? What are some best practices?

johnscott: I'm also trying to run the project from 6v (two 3v coin cells). The batteries in series have at most 500 mAh and the circuit might need to draw maybe 25 - 100 mAh. I used a calculator and it said I could use a 10 - 40ohm resistor. Can anyone with more knowledge double check? What are some best practices?

mAh is Milliamps per hour. It's a term of power such as battery capacity, not current. A simple diode in series, like a 1n4001 or similar, will drop .6V, but since you didn't say which Arduino board you are using, we are only able to guess how you plan to power the board.

SteveMann: mAh is Milliamps per hour. It's a term of power such as battery capacity, not current.

  • milliamp hours, not per hour
  • it's a surrogate for energy, not power

I used a calculator and it said I could use a 10 - 40ohm resistor.

A resistor won't work... The current depends on the brightness and color (and the voltage drop across the resistor is proportional to current). When the LED is off or very-dim, power is still supplied to the built-in chip and there is very-little voltage drop across the resistor.

A diode will probably work. The specs say a maximum of 5.3V so you are "on the edge". That doesn't mean the chip will instantly die at 5.4V and it might work up to 6V etc., but you can't complain if it slightly over 5.3V kills it.

Absolute max parameters show you should be okay 6V, and rapidly dropping.

johnscott: I'm also trying to run the project from 6v (two 3v coin cells).

To run WS2812 LEDs?

You are kidding surely? :cold_sweat:


So, the CR2032 "coin" cell has a rating of 225 mAH so where you get the idea of 500 mAH I cannot imagine.

If you want to power WS2812s I suggest you start with the larger CR2477 cell (or the rechargeable LIR2477 version but you would need a special charger for two of these). :grinning:

You can run WS2812B's on very little current, provided you never drive them over a tiny fraction of the maximum brightness. I have a strip of 60 running perfectly well from a Pro Mini. The sketch limits the brightness settings such that the total current never exceeds 600mA. Having said that, your coin cells won't last more than a few minutes. I would suggest a Li-Ion and voltage converter instead, unless you have space limitations.

How are you powering the processor? Most of them can't handle 6V.

A diode can still be used. It'll drop to 5.3v typical and it'll be safe to run most 5v processors including all of AVR (Arduino)