Datasheet

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-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.

#define VBATPIN A7

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);

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)

Average Power Draw w/SD Card

The average power draw of the ATSAMD21 + regulator circuitry is 11mA. Both the red and green LED each draw

1mA if you light them up.

Say you are running this sample sketch which logs the analog voltage on A0 to an SD card file once a second.

#include <SPI.h>

#include <SD.h>

// Set the pins used

#define cardSelect 4

File logfile;

// blink out an error code

void error(uint8_t errno) {

while(1) {

uint8_t i;