Datasheet

Then the familiar RTC.now() call to get a snapshot of the time. Once we have that, we write

a timestamp (seconods since 2000) as well as the date in YY/MM/DD HH:MM:SS time

format which can easily be recognized by a spreadsheet. We have both because the nice

thing about a timestamp is that its going to montonically increase and the nice thing about

printed out date is its human readable

Log sensor data

Next is the sensor logging code

This code is pretty straight forward, the processing code is snagged from our earlier tutorial.

Then we just print() it to the card with a comma seperating the two

We finish up by turning the green LED off

int photocellReading = analogRead(photocellPin);

delay(10);

int tempReading = analogRead(tempPin);

// converting that reading to voltage, for 3.3v arduino use 3.3

float voltage = tempReading * 5.0 / 1024;

float temperatureC = (voltage - 0.5) * 100 ;

float temperatureF = (temperatureC * 9 / 5) + 32;

logfile.print(", ");

logfile.print(photocellReading);

logfile.print(", ");

logfile.println(temperatureF);

#if ECHO_TO_SERIAL

Serial.print(", ");

Serial.print(photocellReading);

Serial.print(", ");

Serial.println(temperatureF);

#endif //ECHO_TO_SERIAL

digitalWrite(greenLEDpin, LOW);

}