Arduino NMEA Parser

According to Wikipedia,

NMEA 0183 is a combined electrical and data specification for communication between marine electronics such as echo sounder, sonars, anemometer, gyrocompass, autopilot, GPS receivers and many other types of instruments. It has been defined by, and is controlled by, the National Marine Electronics Association.

NMEA 0183 is simple to use and quite robust communication standard as we can verify the integrity of a message using checksum. Arduino NMEA Parser is a library created to simplify the process of verifying and extracting all fields in an NMEA 0183 statement being transmitted through a serial stream. Thus, enabling you to send and receive non-standard NMEA sentences. For example, you can send and receive sensor data in NMEA 0183 format and let this library handles verification part of it.

Usage

To use the library:

1. Download and install the library in Arduino default library folder:

   Refer to this tutorial

2. Include the library in your sketch:

    #include <NmeaParserV2.h>
   

3. Initialize the NmeaParserV2 object:

    // If you are using hardware serial:
    NmeaParserV2 parser(Serial1);
   
    // If you are using SoftwareSerial:
    SoftwareSerial ss(2, 3);
    NmeaParserV2 parser(ss);
   

4. Open stream:

    void setup() {
        // Make sure you are using the correct baud rate
   
        Serial1.begin(9600); // If you are using hardware serial
        ss.begin(9600); // If you are using SoftwareSerial
    }
   

5. Check if any valid NMEA statement is available to be processed:

    void loop() {
        if(parser.valid()) {
            // Do something here...
        }
    }
   

API

• bool valid()

  Reads all available serial bytes until a statement is parsed or the buffer is empty. Returns true if statement is valid.

• byte getFieldCount()

  Returns number of fields parsed.

• char *getField(byte index)

  Returns a field.

• char *getRawStatement()

  Returns a raw NMEA statement.

• char prepareStatement()

  Resets the statement to be sent. Called once by the constructor and everytime send function is called.

• void append(char *cArray, byte length);

  An overloaded function to append data to the statement to be sent. cArray is the char array to append to the the statement. length is the length of the cArray.

• void append(int value);

  An overloaded function to append data to the statement to be sent. value is the integer value to pass to the statement.

• void append(long value);

  An overloaded function to append data to the statement to be sent. value is the long integer value to pass to the statement.

• void append(double value, byte totalLength, byte mantissaLength);

  An overloaded function to append data to the statement to be sent. value is the double value to pass to the statement. totalLength refers to the total length of a floating number including the decimal point and mantissa. Example: totalLength for 123.456 is 7. mantissaLength refers to the length of the mantissa, the decimal places. Example: mantissaLength for 123.456 is 3.

• void send();

  Generate checksum and send the statement through stream channel. This function will automatically calls prepareStatement function.

Constants

You may modify the following constants if you need to, but remember that this will also increase memory usage.

NmeaParserV2_MAX_FIELD_COUNT (default: 20)

This value determines maximum number of fields in an NMEA statement. Should be a value between 1 and 255 inclusive.

NmeaParserV2_MAX_FIELD_LENGTH (default: 15)

This value determines maximum character length in each field. Should be a value between 1 and 255 inclusive.

NmeaParserV2_MAX_SEND_STATEMENT_LENGTH (default: 270)

This value determines maximum character length in send statement.

Others

Please note that both hardware and software serial suffers from inadequate buffer size when dealing with fast data transmission or large amount of data to be processed. If you are not getting valid NMEA statement, try to increase the serial buffer size. Refer this page for more information.

Basically, you need to increase the buffer size of the streams.

For SoftwareSerial, modify the following file:

```cpp
// <Arduino installation folder>\hardware\arduino\avr\libraries\SoftwareSerial\SoftwareSerial.h
// and modify the following line:

#define _SS_MAX_RX_BUFF 64 // From this
#define _SS_MAX_RX_BUFF 256 // To this
```

For HardwareSerial, modify the following file:

```cpp
// <Arduino installation folder>\hardware\arduino\avr\cores\arduino\HardwareSerial.h
// and modify the following line:

#define SERIAL_TX_BUFFER_SIZE 64 // From this
#define SERIAL_TX_BUFFER_SIZE 256 // To this
```

However, please note that by increasing those values, you are also increasing the SRAM used by the Arduino, limiting the available memory for your sketch.