Datasheet

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-100K resistor divider on the BAT pin, and connected it to D9 (a.k.a analog #7 A7).

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

This voltage will 'float' at 4.2V when no battery is plugged in, due to the lipoly charger output, so its not a good way to

detect if a battery is plugged in or not (there is no simple way to detect if a battery is plugged in)

Alternative Power Options

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

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 (https://adafru.it/duP) 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! (https://adafru.it/e2q)

If you have a higher voltage power supply, use a 5V buck converter (https://adafru.it/DHs) and wire it to a USB

cable's 5V and GND input (https://adafru.it/DHu)

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

#define VBATPIN A9

float measuredvbat = analogRead(VBATPIN);

measuredvbat *= 2; // we divided by 2, so multiply back

measuredvbat *= 3.3; // Multiply by 3.3V, our reference voltage

measuredvbat /= 1024; // convert to voltage

Serial.print("VBat: " ); Serial.println(measuredvbat);

https://learn.adafruit.com/adafruit-feather-32u4-radio-with-rfm69hcw-

module

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