Datasheet

create LOGGER00.CSV and incrementing every time when the file already exists, until we

get to LOGGER99.csv, we basically make a new file every time the Arduino starts up

To create a file, we use some Unix style command flags which you can see in the

logfile.open() procedure. FILE_WRITE means to create the file and write data to it.

Assuming we managed to create a file successfully, we print out the name to the Serial

port.

Wire.begin();

if (!RTC.begin()) {

logfile.println("RTC failed");

#if ECHO_TO_SERIAL

Serial.println("RTC failed");

#endif //ECHO_TO_SERIAL

}

logfile.println("millis,time,light,temp");

#if ECHO_TO_SERIAL

Serial.println("millis,time,light,temp");

#if ECHO_TO_SERIAL// attempt to write out the header to the file

if (logfile.writeError || !logfile.sync()) {

error("write header");

}

pinMode(redLEDpin, OUTPUT);

pinMode(greenLEDpin, OUTPUT);

// If you want to set the aref to something other than 5v

//analogReference(EXTERNAL);

}

OK we're wrapping up here. Now we kick off the RTC by initializing the Wire library and

poking the RTC to see if its alive.

Then we print the header. The header is the first line of the file and helps your spreadsheet

or math program identify whats coming up next. The data is in CSV (comma separated

value) format so the header is too: "millis,time,light,temp" the first item millis is milliseconds

since the Arduino started, time is the time and date from the RTC, light is the data from

the CdS cell and temp is the temperature read.

You'll notice that right after each call to logfile.print() we have #if ECHO_TO_SERIAL and

a matching Serial.print() call followed by a #if ECHO_TO_SERIAL this is that debugging

output we mentioned earlier. The logfile.print() call is what writes data to our file on the SD

card, it works pretty much the same as the Serial version. If you set ECHO_TO_SERIAL to

be 0 up top, you won't see the written data printed to the Serial terminal.