Battery + USB Power

We wanted to make our Feather boards easy to power both when connected to a computer as well as via battery.

There's two ways to power a Feather:

You can connect with a USB cable (just plug into the jack) and the Feather will regulate the 5V USB down to 3.3V.
You can also connect a 4.2/3.7V Lithium Polymer (LiPo/LiPoly) or Lithium Ion (LiIon) battery to the JST jack. This will let the Feather run on a rechargeable battery.

When the USB power is powered, it will automatically switch over to USB for power, as well as start charging the battery (if attached). This happens 'hot-swap' style so you can always keep the LiPoly connected as a 'backup' power that will only get used when USB power is lost.

The JST connector polarity is matched to Adafruit LiPoly batteries. Using wrong polarity batteries can destroy your Feather. Many customers try to save money by purchasing Lipoly batteries from Amazon only to find that they plug them in and the Feather is destroyed!

The above shows the USB-C jack (left), LiPoly JST jack (top left), as well as the changeover diode (just to the right of the JST jack) and the LiPoly charging circuitry (to the right of the JST jack).

There's also a CHG LED next to the USB jack, which will light up while the battery is charging. This LED might also flicker if the battery is not connected, it's normal.

The charge LED is automatically driven by the LiPoly charger circuit. It will try to detect a battery and is expecting one to be attached. If there isn't one it may flicker once in a while when you use power because it's trying to charge a (non-existent) battery. It's not harmful, and it's totally normal!

Power Supplies

You have a lot of power supply options here! We bring out the BAT pin, which is tied to the LiPoly JST connector, as well as USB which is the +5V from USB if connected. We also have the 3V pin which has the output from the 3.3V regulator. We use a 500mA peak regulator. While you can get 500mA from it, you can't do it continuously from 5V as it will overheat the regulator.

It's fine for, say, powering an ESP8266 WiFi chip or XBee radio though, since the current draw is 'spikey' & sporadic.

Measuring Battery

If you're running off of a battery, chances are you wanna know what the voltage is at! That way you can tell when the battery needs recharging. LiPoly batteries are 'maxed out' at 4.2V and stick around 3.7V for much of the battery life, then slowly sink down to 3.2V or so before the protection circuitry cuts it off. By measuring the voltage you can quickly tell when you're heading below 3.7V.

To make this easy we stuck a double-200K resistor divider on the BAT pin, and connected it to A13 which is not exposed on the feather breakout.

In Arduino, you can read this pin's voltage, then double it, to get the battery voltage.

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// Arduino Example Code snippet

#define VBATPIN A13

float measuredvbat = analogReadMilliVolts(VBATPIN);
measuredvbat *= 2;    // we divided by 2, so multiply back
measuredvbat /= 1000; // convert to volts!
Serial.print("VBat: " ); Serial.println(measuredvbat);

// Arduino Example Code snippet

#define VBATPIN A13

float measuredvbat = analogReadMilliVolts(VBATPIN);
measuredvbat *= 2;    // we divided by 2, so multiply back
measuredvbat /= 1000; // convert to volts!
Serial.print("VBat: " ); Serial.println(measuredvbat);

ENable pin

If you'd like to turn off the 3.3V regulator, you can do that with the EN(able) pin. Simply tie this pin to Ground and it will disable the 3V regulator. The BAT and USB pins will still be powered.

STEMMA QT Power

The ESP32 Feather V2 is equipped with a STEMMA QT port which is connected to its own regulator. Unlike the one controlled by the ENable pin, this one is controlled by GPIO. The NeoPixel and STEMMA power pin is enabled by default in Arduino. You can disable it manually for low power usage. The pin is available in Arduino as NEOPIXEL_I2C_POWER.

If you run into NeoPixel or I2C power issues on Arduino, ensure you are using the latest Espressif board support package. If you are still having issues, you may need to manually pull the pin high in your code.

Alternative Power Options

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

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

For permanent installations, a 5V 1A USB wall adapter will let you plug in a USB cable for reliable power
For mobile use, where you don't want a LiPoly, use a USB battery pack!
If you have a higher voltage power supply, use a 5V buck converter and wire it to a USB cable's 5V and GND input

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 work. 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.