I am using a Arduino Uno with a Adafruit Ultimate GPS logger.
The code is primarily the adafruit sample code, but I changed it for two reasons:
- To limit the amount of data recorded to what I needed.
- To include voltage data logged through the analog ports.
It basically works, but the GPS data seems to be written onto the SD card twice for each 0.2 sec cycle. I’ve included the entire code here, but my question mostly concerns the logfile.print() commands I substituted for the sample code logfile.write() section (commented out below), which I honestly do not understand.
The code needs to run at 5Hz, which works this way but can be a problem with some other logging options. I also need GGA data for the altitude component.
#include <SPI.h> #include <Adafruit_GPS.h> #include <SoftwareSerial.h> #include <SD.h> #include <avr/sleep.h> // Ladyada's logger modified by Bill Greiman to use the SdFat library // // This code shows how to listen to the GPS module in an interrupt // which allows the program to have more 'freedom' - just parse // when a new NMEA sentence is available! Then access data when // desired. // Fllybob added 10 sec logging option SoftwareSerial mySerial(8, 7); Adafruit_GPS GPS(&mySerial); // Set GPSECHO to 'false' to turn off echoing GPS data to the Serial console // Set to 'true' if you want to debug and listen to the raw GPS sentences #define GPSECHO false /* set to true to only log to SD when GPS has a fix, for debugging, keep it false */ #define LOG_FIXONLY false int Li=A0; //Lf assigned to port A0 int Lf=A1; int Lo=A2; int LiValue; int LfValue; int LoValue; // this keeps track of whether we're using the interrupt // off by default! boolean usingInterrupt = false; void useInterrupt(boolean); // Func prototype keeps Arduino 0023 happy // Set the pins used #define chipSelect 10 #define ledPin 13 File logfile; // read a Hex value and return the decimal equivalent uint8_t parseHex(char c) { if (c < '0') return 0; if (c <= '9') return c - '0'; if (c < 'A') return 0; if (c <= 'F') return (c - 'A')+10; } // blink out an error code void error(uint8_t errno) { /* if (SD.errorCode()) { putstring("SD error: "); Serial.print(card.errorCode(), HEX); Serial.print(','); Serial.println(card.errorData(), HEX); } */ while(1) { uint8_t i; for (i=0; i<errno; i++) { digitalWrite(ledPin, HIGH); delay(100); digitalWrite(ledPin, LOW); delay(100); } for (i=errno; i<10; i++) { delay(200); } } } void setup() { // for Leonardos, if you want to debug SD issues, uncomment this line // to see serial output //while (!Serial); pinMode(Li,INPUT); pinMode(Lf,INPUT); pinMode(Lo,INPUT); // connect at 115200 so we can read the GPS fast enough and echo without dropping chars // also spit it out Serial.begin(115200); Serial.println("\r\nUltimate GPSlogger Shield"); pinMode(ledPin, OUTPUT); // make sure that the default chip select pin is set to // output, even if you don't use it: pinMode(10, OUTPUT); // see if the card is present and can be initialized: if (!SD.begin(chipSelect)) { // for an UNO, use this line instead Serial.println("Card init. failed!"); error(2); } char filename[15]; strcpy(filename, "GPSLOG00.CSV"); for (uint8_t i = 0; i < 100; i++) { filename[6] = '0' + i/10; filename[7] = '0' + i%10; // create if does not exist, do not open existing, write, sync after write if (! SD.exists(filename)) { break; } } logfile = SD.open(filename, FILE_WRITE); if( ! logfile ) { Serial.print("Couldnt create "); Serial.println(filename); error(3); } Serial.print("Writing to "); Serial.println(filename); // connect to the GPS at the desired rate GPS.begin(9600); // uncomment this line to turn on RMC (rec minimum) and GGA (fix data) GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCGGA); // uncomment this line to turn on only the "minimum recommended" data //GPS.sendCommand(PMTK_SET_NMEA_OUTPUT_RMCONLY); // For logging data, we suggest either RMC only or RMC+GGA // to keep the log files at a reasonable size // Set the update rate GPS.sendCommand(PMTK_SET_NMEA_UPDATE_5HZ); // Turn off updates on antenna status, if the firmware permits it GPS.sendCommand(PGCMD_NOANTENNA); // the nice thing about this code is you can have a timer0 interrupt go off // every 1 millisecond, and read data from the GPS for you. that makes the // loop code a heck of a lot easier! useInterrupt(true); Serial.println("Ready!"); } // Interrupt is called once a millisecond, looks for any new GPS data, and stores it SIGNAL(TIMER0_COMPA_vect) { char c = GPS.read(); // if you want to debug, this is a good time to do it! #ifdef UDR0 if (GPSECHO) if (c) UDR0 = c; // writing direct to UDR0 is much much faster than Serial.print // but only one character can be written at a time. #endif } void useInterrupt(boolean v) { if (v) { // Timer0 is already used for millis() - we'll just interrupt somewhere // in the middle and call the "Compare A" function above OCR0A = 0xAF; TIMSK0 |= _BV(OCIE0A); usingInterrupt = true; } else { // do not call the interrupt function COMPA anymore TIMSK0 &= ~_BV(OCIE0A); usingInterrupt = false; } } void loop() { if (! usingInterrupt) { // read data from the GPS in the 'main loop' char c = GPS.read(); // if you want to debug, this is a good time to do it! if (GPSECHO) if (c) Serial.print(c); } LiValue = analogRead(Li); LfValue = analogRead(Lf); LoValue = analogRead(Lo); // if a sentence is received, we can check the checksum, parse it... if (GPS.newNMEAreceived()) { // a tricky thing here is if we print the NMEA sentence, or data // we end up not listening and catching other sentences! // so be very wary if using OUTPUT_ALLDATA and trying to print out data // Don't call lastNMEA more than once between parse calls! Calling lastNMEA // will clear the received flag and can cause very subtle race conditions if // new data comes in before parse is called again. char *stringptr = GPS.lastNMEA(); if (!GPS.parse(stringptr)) // this also sets the newNMEAreceived() flag to false return; // we can fail to parse a sentence in which case we should just wait for another // Sentence parsed! Serial.println("OK"); if (LOG_FIXONLY && !GPS.fix) { Serial.print("No Fix"); return; } // Rad. lets log it! Serial.println("Log"); logfile.print(GPS.hour, DEC); logfile.print(":"); logfile.print(GPS.minute, DEC); logfile.print(':'); logfile.print(GPS.seconds, DEC); logfile.print('.'); logfile.print(GPS.milliseconds); logfile.print(","); logfile.print(GPS.day, DEC); logfile.print('/'); logfile.print(GPS.month, DEC); logfile.print(","); logfile.print(GPS.latitude, 4); logfile.print(", "); logfile.print(GPS.lat); logfile.print(", "); logfile.print(GPS.longitude, 4); logfile.print(", "); logfile.print(GPS.lon); logfile.print(","); logfile.print(GPS.altitude); logfile.print(","); logfile.print(LiValue); logfile.print(","); logfile.print(LfValue); logfile.print(","); logfile.println(LoValue); // uint8_t stringsize = strlen(stringptr); // if (stringsize != logfile.write((uint8_t *)stringptr, stringsize)) //write the string to the SD file // error(4); if (strstr(stringptr, "RMC") || strstr(stringptr, "GGA")) logfile.flush(); Serial.println(); } } /* End code */ 
