A LoRa GPS tracker sensor based on

• Arduino Uno and
• Dragino LoRa GPS Shield

for use in LoRaWAN networks.

This application transmits

• current GPS position,
• altitude and
• hdop

as soon as a GPS fix is aquired. This data is sent continously using LMIC library. The device is powered by any source that fits to Arduino Uno.

We use this tracker to measure the range of the LoRaWAN Gateways in our network. The application's output format is compatible for use with TTN Mapper.

It might suite for any other GPS tracking use case as well. We just included to the values we required but it can easily be extended to more values. Keep in mind that more data means longer transmission times and duty cycles, especially on high spreading factors.

What you need:

• Arduino Uno and
• Dragino LoRa GPS Shield
• power source for powering Arduino

Put together the hardware as described in the vendor's manual.

Create an application in The Things Network Console and add a new device. Use ABP as activation method. Disable Frame Counter Checks.

Change the

• NWKSKEY
• APPSKEY
• DEVADDR

values in the code according to match the device details you just created in the TTN Console.

Adjust the channel configuration if you use it outside EU.

Program the application to your Arduino Uno. If you have problems while programming, try pressing the reset button of the Shield during programming.

In The Things Network Console you can use this code to decode uplink messages:

function Decoder(bytes, port) {
    // Decode an uplink message from a buffer
    // (array) of bytes to an object of fields.
    var decoded = {};
    // if (port === 1) decoded.led = bytes[0];
    decoded.lat = ((bytes[0] << 16) >>> 0) + ((bytes[1] << 8) >>> 0) + bytes[2];
    decoded.lat = (decoded.lat / 16777215.0 * 180) - 90;
    decoded.lon = ((bytes[3] << 16) >>> 0) + ((bytes[4] << 8) >>> 0) + bytes[5];
    decoded.lon = (decoded.lon / 16777215.0 * 360) - 180;
    var altValue = ((bytes[6] << 8) >>> 0) + bytes[7];
    var sign = bytes[6] & (1 << 7);
    if (sign) {
        decoded.alt = 0xFFFF0000 | altValue;
    } else {
        decoded.alt = altValue;
    }
    decoded.hdop = bytes[8] / 10.0;
    return decoded;
}

Optionally you can adjust these values:

• TX_INTERVAL Defines the pause time in seconds between transmissions (default is 60. You can set it to 0 to get as many data as possible and use the maximum duty cycle allowed.)
• GPS_INTERVAL poll interval of GPS DATA
• lmic_pinmap PIN mapping matches Dragino LoRa GPS shield. Adjust if your are using a different shield.
• LMIC_setDrTxpow Spreading Factor (SF7 -> SF12) and transmission power in dB
• Debug Mode (DEBUG_SS) see chapter Debug mode
• channel operation by removing the comments from the channel definition you can use all LoRaWAN channels for EU868 suggested by The Things Network.

Debug mode enables debugging of the reception of GPS data via SoftSerial. On Arduino Uno it is not possible to run debug mode and LoRa transmission at the same time due to memory restrictions. To enable debug mode define DEBUG_SS:

#define DEBUG_SS

Create an Access Key for TTN Mapper in your TTN application. Send a message to the owner of TTN Mapper including your application name and access key. You find the details in the Contact menu at http://ttnmapper.org.

As soon as you get confirmation your data will automatically show up.

Press the reset button of the Shield while programming.

Check that you have disabled Frame Counter Checks in the device configuration of TTN Console.

The LoRa GPS tracker transmits on the 3 default channels of LMIC (EU868). You can disable the unwanted channels by looking for these lines in the code:

// disable channels not known to single channel gateways
LMIC_disableChannel(1);  // uncomment to disable channel 1
LMIC_disableChannel(2);  // uncomment to disable channel 2
[...]

The LoRa GPS tracker transmits on the 3 default channels of LMIC (EU868). You can remove the comments from the channel definition to enable additional channels:

// LMIC_setupChannel(0, 868100000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);
// LMIC_setupChannel(1, 868300000, DR_RANGE_MAP(DR_SF12, DR_SF7B), BAND_CENTI);
// LMIC_setupChannel(2, 868500000, DR_RANGE_MAP(DR_SF12, DR_SF7),  BAND_CENTI);
[...]

This should be possible. You will have to adjust the PIN mapping constant called lmic_pinmap. For GPS a serial port with 9600 baud is used.

This script is based on the work by Thomas Telkamp, Matthijs Kooijman and Andreas Spiess. Thanks for ttnmapper application and code review to JP Meijers.