0

Adafruit HUZZAH ESP8266 breakout - driving NeoPixel strip
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Adafruit HUZZAH ESP8266 breakout - driving NeoPixel strip

by rmetcalf9 on Fri Nov 30, 2018 10:17 am

Hi,

I want my HUZZAH ESP8266 breakout to drive 15 neopixels. (I have a 60 LED per meter strip which groups the pixels in 3's and I have cut it to have 15 pixels.)

Based on this guide: https://learn.adafruit.com/adafruit-neo ... -neopixels
the max power usage of each pixel is 60 miliamps but I won't be using full brightness so I am going by their 1/3 of this rule of thumb.

So I think my neopixels will use 15 * 20 = 300 miliamps, and the chip itself uses 250-500 miliamps so my powersupply should be good enough.

I plan to connect the + of the neopixel strip to the 3v pin and the - to the GND pin. Also as per the instructions ut a 470ohm resistor on the data line and use pin 14.
(https://learn.adafruit.com/adafruit-huz ... ut/pinouts)

My question is about the 1000 uF capacitor the guide says I should use to protect against inrush current.
    - Do I still need it if I am driving the neopixel directly from the board? My other project didn't and everything is working
    - What type of capacitor should I use.
    - Am I right in guessing that the + on the capacitor should go to the 3v pin and the - go to the gnd?
    - Am I right in guessing that the capacitor needs to be as close to the board as possible?
Also before I get my soldiering iorn out do I have any other fundamental floors?

I forgot to mention - I am driving this by a mobile phone usb power supply.

Thanks
Robert

rmetcalf9
 
Posts: 3
Joined: Tue Nov 27, 2018 2:12 pm

Re: Adafruit HUZZAH ESP8266 breakout - driving NeoPixel stri

by adafruit_support_mike on Sat Dec 01, 2018 2:03 am

You probably won't need a 1000uF capacitor for a strip that short.

The capacitor's job is to reduce voltage spikes that happen when the NeoPixel LEDs turn on and off. Each pixel only creates a small spike on its own, but if you add the spikes from 50 or 60 pixels together, you get something big enough to cause trouble.

For future reference, the only capacitors in that value will be electrolytic, and yes, it's important to connect the positive lead of an electrolytic cap to the positive voltage. If you reverse the connections, the cap can explode.

Electrolytic capacitors are made from two layers of aluminum foil with a layer of paper soaked in a conductive liquid (the 'electrolyte') between them. One layer of foil has direct contact with the electrolyte, and the electrolyte takes the same voltage as that piece of foil. The other piece of foil has tiny pits etched in its surface, giving it a lot of surface area, and the etched surface has a very thin layer of non-conductive insulation between the foil and the electrolyte. High-value capacitors need plates with a lot of surface area and a thin conductive layer between them, and the electrolytic structure does that. The etched foil is one plate, and the electrolyte is the other plate.

If there are any holes in the insulating oxide layer, current will flow from the electrolyte to the foil at those points. The electrolyte is also a plating medium though, so the current flowing into exposed foil will automatically pull molecules that create an oxide layer to the gaps in the insulation, closing them.

If you reverse the connections, connecting negative voltage to the etched layer, the plating process will work the other way, stripping the insulating layer away from the foil, and creating regions of bare foil where current can flow. The current heats up the electrolyte, and when it gets hot enough, the water in the electrolyte will turn to steam. If the current creates an arc (several thousand degrees), the electrolyte flashes to steam quickly, and the aluminum can around the foil turns into a bomb.

Electrolytic cans have score marks that should make the can fail at known and relatively safe points, but that doesn't stop an exploding cap from being exciting. They have about the same explosive force as bullets or shotgun shells.


Coming back to your project, you'll want to connect the NeoPixel strip's positive supply rail to the 5V terminal of the USB power supply instead of the ESP8266 breakout's 3V pin.

First, the breakout's 3.3V regulator is made to handle 600mA. That's enough to handle the ESP8266's 500mA burst current, but doesn't leave enough extra current for a NeoPixel strip. Second, and probably more important, the blue LEDs in a NeoPixel strip can't light up from a 3.3V supply. The LEDs themselves need about 3.3V, and then there's some additional voltage for the switch and current regulator.

A NeoPixel strip connected to 5V power won't cause any problems for a 3.3V ESP8266 though. The first pixel's data-in pin isn't connected to the pixel's 5V supply, so it won't damage the ESP8266's GPIO pin. Technically the NeoPixels will want 5V data signals, but we've found that our strips tend to accept 3.3V data signals without any trouble.

adafruit_support_mike
 
Posts: 59421
Joined: Thu Feb 11, 2010 2:51 pm

Re: Adafruit HUZZAH ESP8266 breakout - driving NeoPixel stri

by rmetcalf9 on Sat Dec 01, 2018 5:48 am

First of all thank you for an awesome response. I learnt a lot and I will be referring back to it in future.
I have altered my designs for my project and I will be using a direct connection from the 5v usb power supply rather than the 3.3 v connection.

I have one further question. My prototype project involved a HUZZAH Feather I followed this design
https://learn.adafruit.com/feather-weat ... it-diagram

except I was driving a smaller 12 neo pixel ring. In this design you connect the +v on the ring to the 3.3v connector on the HUZZAH feather. I have just checked it now and it can show blue without a problem.

Is there a difference between the 3.3v connector on the HUZZAH break out board vs the HUZZAH feather board? Or are Neo Pixel strips different from the 12 Neo Pixel rings?

Thanks again for your answers

rmetcalf9
 
Posts: 3
Joined: Tue Nov 27, 2018 2:12 pm

Re: Adafruit HUZZAH ESP8266 breakout - driving NeoPixel stri

by adafruit_support_mike on Mon Dec 03, 2018 1:37 am

All of our NeoPixel boards and strips use the same pixels. It's better to use the 5V power source if you have one though.

adafruit_support_mike
 
Posts: 59421
Joined: Thu Feb 11, 2010 2:51 pm

Please be positive and constructive with your questions and comments.