Reduce the power consumption feather adalogger M0

[krx7]

Hello,
I would like to put a Feather Adalogger in deep sleep after it has read the data from a temperature and humidity sensor every 5 minutes.
I found the Low_Power library and Adafruit_SleepyDog .
While searching further I found various information and code, but I'm not shure about the best way to put into sleep mode or standby the feather.

#include <SD.h>
#include "RTClib.h"
#include "DHT.h"

#define VBATPIN A7    // Battery Voltage on Pin A7
#define DHTPIN 5        // what pin the sensor is connected to
#define DHTTYPE DHT11   // Which type of DHT sensor you're using: 
RTC_DS3231 rtc;

// initialize the sensor:
DHT dht(DHTPIN, DHTTYPE);

const int chipSelect = 4;         // SPI chip select for SD card
const int cardDetect = 7;          // pin that detects whether the card is there
const int writeLed = 8;           // LED indicator for writing to card
const int errorLed = 13;          // LED indicator for error
long lastWriteTime = 0;           // timestamp for last write attempt
long interval = 5000;            // time between readings
char fileName[] = "datalog.csv";  // filename to save on SD card

void setup() {
 Serial.begin(9600);   // initialize serial communication


 if (! rtc.begin()) {
    Serial.println("Couldn't find RTC");
    Serial.flush();
    while (1) delay(10);
  }

  if (rtc.lostPower()) {
    Serial.println("RTC lost power, let's set the time!");
    // When time needs to be set on a new device, or after a power loss, the
    // following line sets the RTC to the date & time this sketch was compiled
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  }

  // initialize LED and cardDetect pins:
  pinMode(writeLed, OUTPUT);
  pinMode(errorLed, OUTPUT);
  pinMode(cardDetect, INPUT_PULLUP);

  // startSDCard() blocks everything until the card is present
  // and writable:
  if (startSDCard() == true) {
    Serial.println("card initialized.");
    delay(100);
    // open the log file:
    File logFile = SD.open(fileName, FILE_WRITE);
    // write header columns to file:
    if (logFile) {
      logFile.println("Date,Hour,Batt");
      logFile.close();
    }
  }

  // initialize the sensor:
   dht.begin();
}

void loop() {
  // if the cart's not there, don't do anything more:
  if (digitalRead(cardDetect) == LOW) {
    digitalWrite(errorLed, HIGH);
    return;
  }
  // turn of the error LED:
  digitalWrite(errorLed, LOW);

  DateTime now = rtc.now();

  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

  // read sensors every 10 seconds
  if (millis()  - lastWriteTime >=  interval) {
    File logFile = SD.open(fileName, FILE_WRITE);   // open the log file
    if (logFile) {                                  // if you can write to the log file,
      digitalWrite(writeLed, HIGH);                 // turn on the write LED


      int day = now.day();
      int month = now.month();
      int year = now.year();
      int hour = now.hour();
      int minute = now.minute();

      int second = now.second();

      // print to the log file: 
      logFile.print(day);
      logFile.print("/");
      logFile.print(month);
      logFile.print("/");
      logFile.print(year);
      logFile.print(", ");
      logFile.print(hour);
      logFile.print(":");
      logFile.print(minute);
      logFile.print(":");
      logFile.print(second);
      logFile.print(", ");
      logFile.println(measuredvbat);   // Print battery voltage
      logFile.print(", ");
      logFile.print(humidity);
      logFile.print(",");
      logFile.println(temperature);
      logFile.flush();

     // for debugging only:
      Serial.print(day);
      Serial.print('/');
      Serial.print(month);
      Serial.print('/');
      Serial.print(year);
      Serial.print(",");
      Serial.print(hour);
      Serial.print(':');
      Serial.print(minute);
      Serial.print(':');
      Serial.print(second);
      Serial.print(",");
      Serial.print(measuredvbat);
      Serial.print(",");
      Serial.print(humidity);
      Serial.print(",");
      Serial.println(temperature);
      Serial.print('\n'); 
      // read sensor:
      float humidity = dht.readTemperature();
      float temperature = dht.readHumidity();

      // update the last attempted save time:
      lastWriteTime = millis();
    }
    digitalWrite(writeLed, LOW);      // turn off the write LED
  }
}

boolean startSDCard() {
  // Wait until the card is inserted:
  while (digitalRead(cardDetect) == LOW) {
    Serial.println("Waiting for card...");
    digitalWrite(errorLed, HIGH);
    delay(750);
  }

  // wait until the card initialized successfully:
  while (!SD.begin(chipSelect)) {
    digitalWrite(errorLed, HIGH);   // turn on error LED
    Serial.println("Card failed");
    delay(750);
  }
  return true;
}

Thanks for your feedback