SparkFun Forums

[wasaler]

Hello everyone,

Quite new here, this being my first post. If you care for an introduction, here is a really short one (if not, skip to the next paragraph ): currently a second year neuroscience student in Canada; found out not too long ago that I like tinkering and making random stuff, but am not very good at it. Started out small with arduino tutorials, and currently looking at a (slightly) more ambitious project.

Anyways! Any help is appreciated for the following:
- I am currently looking to design a custom PCB onto which I will be mounting the WS2812 LEDs. In doing some research though, I am confused as to what components I should include on top of the barebones WS2811 driver + LED package:
Schematics for an Adafruit design show use of capacitors and resistors (example: https://github.com/adafruit/Adafruit...d_NeoPixel_PCB), whereas SparkFun show use of only a single 0.1microF capacitor (https://dlnmh9ip6v2uc.cloudfront.net...1-Breakout.pdf)

So when I'm designing my own PCB, what are the pros and cons of including/excluding these extra capacitors and resistors?

Thanks!

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(If anyone feels like answering the following, that'd be great as well, but these are less urgent matters:

- Assuming I wanted to move away from using a ready made Arduino board, and create my own (likely will be based on the ATMega 328), what are the essential components other than the microcontroller that I should include just to drive the above LEDs? Unessential components include things like indicator LEDs, pin jacks, etc. This board would be integrated in a project with the LEDs and wouldn't need to be as versatile as the Arduino is.

[Ross Robotics]

Your links don't work. Please just paste the entire link in a post.

This is what a bare arduino schematic could look like. http://arduino4projects.com/wp-content/ ... rduino.jpg You could change the FTDI header for an ICSP header if you want to program that way.

[wasaler]

My apologies, here are the fixed links:

Adafruit: https://github.com/adafruit/Adafruit_Br ... oPixel_PCB
SparkFun: https://dlnmh9ip6v2uc.cloudfront.net/da ... eakout.pdf

Again, the question was: why the two configurations? i.e. one with just one capacitor, the other with a cap and 3 resistors?

[Ross Robotics]

Sparkfun's board is just a break out board. So you can adjust the values on the current limiting resistors. The Adafruit board has a set consumption current. Read the datasheet for typical application circuit. The cap is only for decoupling. It should always be there and a value of 0.1uF is standard.

[Kerbal]

Most breakout boards are just the recommended application, in the recommended layout, straight out of the datasheet.

The LED chips use an oscillator to communicate and to PWM the LEDs. Without a capacitor, the oscillator frequency would ripple up and down with the voltage causing "packet loss" or a "twinkling" of the LEDs. Turning the third LED in series on full intensity white could essentially brown-out the first and second chips. Once a chip browns-out, it cannot transmit data downstream and the rest of the strand would remain unlit. The effect would be more and more severe for each chip in series. A cap is used for each chip to ensure they all run at the same and correct voltage/speed.

On the resistive side, both boards will contain any resistors required by the part, but may have additional resistors for just-in-case or CYA purposes. Basically, "things happen" (especially with new-comers).
You want "device failure" to mean the LED isn't as bright as you'd like.. and not that it caught fire and exploded.