I have a Huzzah Feather ESP8266 (pinout) and due to the requirements of my project, I need to supply it with a 9V power adapter with a barrel connector, such as this one. I'm REALLY new to all of this, so I am trying to figure out how to do this and understand reading dev board specs.

It looks like this development board has a regulator that will adjust a power source down to the appropriate voltage... but how do I know what parameters it allows?

If I'm understanding correctly, on the pinout sheet above it looks like I would connect a power supply to the "VBUS" and "GND" (right?) pins. It also says "500mA Max", so does that mean a 1A power supply won't work? Also, why wouldn't it specify a maximum voltage?

If just connecting a barrel connector to those pins will not work, what am I missing that would get me there?

  • Have you seen this forum thread?
    – chrisl
    Feb 7, 2020 at 21:15
  • just use a cheap buck dc-dc converter to feed it 3.3v or whatever
    – dandavis
    Feb 7, 2020 at 22:34

2 Answers 2


You cannot. If you look at the datasheet:


you can read all details on page 25/26:

Alternative Power Options

The two primary ways for powering a feather are a 3.7/4.2V LiPo battery plugged into the JST portor a USB power cable.

If you need other ways to power the Feather, here's what we recommend:

Here's what you cannot do:

  • Do not use alkaline or NiMH batteries and connect to the battery port - this will destroy the LiPoly charger and there's no way to disable the charger
  • Do not use 7.4V RC batteries on the battery port - this will destroy the board

The Feather is not designed for external power supplies - this is a design decision to make the board compact and low cost. It is not recommended, but technically possible:

  • Connect an external 3.3V power supply to the 3V and GND pins. Not recommended, this may cause unexpected behavior and the EN pin will no longer. Also this doesn't provide power on BAT or USB and some Feathers/Wings use those pins for high current usages. You may end up damaging your Feather.
  • Connect an external 5V power supply to the USB and GND pins. Not recommended, this may cause unexpected behavior when plugging in the USB port because you will be back-powering the USB port, which could confuse or damage your computer.

If you read the docs on that Feather board, the barrel connector is meant for a LiPo battery.

It's a 3V unit, not meant for an external power supply, and 9V is too much for it. You would need to run your 9V supply through a buck converter (or a linear regulator) and drop it down to 5V, which you could feed into the USB connector. That does mean that when you want to connect it to USB to power it it will lose power, unless you also plug a LiPo battery into the barrel connector.

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