Talking Bytes with The Things Network

add_buffer_gps.cpp

void add_buffer_gps(double lat, double lon){

  // offset by 90(180) to make positive and scale to 0..1
  latB = ((lat + 90) / 180.0) * pow(256,3);
  lonB = ((lon + 180) / 360.0) * pow(256,3);

  // byte shifting
  dataBuffer[0] = ( latB >> 16 ) & 0xFF;
  dataBuffer[1] = ( latB >> 8 ) & 0xFF;
  dataBuffer[2] = latB & 0xFF;

  dataBuffer[3] = ( lonB >> 16 ) & 0xFF;
  dataBuffer[4] = ( lonB >> 8 ) & 0xFF;
  dataBuffer[5] = lonB & 0xFF;
  }

datapoint.json

{"_id": "5b377f54e4d28c0006c1ab93",
  "deviceId":"ttn-uno",
  "receivedAt":"2018-06-30T13:02:12.565Z",
  "metadata":{
    "time":"2018-06-30T13:02:12.339076452Z",
    "frequency":868.1,
    "modulation":"LORA",
    "data_rate":"SF7BW125",
    "airtime":66816000,
    "coding_rate":"4/5",
    "gateways":[
      {"gtw_id":"eui-0000024b080310b1",
        "timestamp":628068507,
        "time":"2018-06-30T13:02:11.414067Z",
        "channel":0,
        "rssi":-117,
        "snr":1.5,
        "rf_chain":1,
        "latitude":47.37787,
        "longitude":8.53909,
        "altitude":433
      }
    ]
  },
  "dist":0,
  "speed":0,
  "temp-inside":16.99981689453125,
  "temp-outside":23.09722900390625,
  "tiltx":0.1875,
  "tilty":-0.203125
}

decode_gps.js

function Decoder (bytes, port) {
  var decoded = {}
  if (port === 1) {
    if (bytes.length === 10) {
      var lat = bytesToInt(bytes.slice(0, 3)) / Math.pow(256, 3) * 180 - 90
      var lon = bytesToInt(bytes.slice(3, 6)) / Math.pow(256, 3) * 360 - 180
      if (lat !== 0 && lon !== 0) {
        decoded['lat'] = lat
        decoded['lon'] = lon
      }

      var tiltx = bytesToInt(bytes.slice(10, 11)) / Math.pow(256, 1) * 4 - 2
      decoded['tiltx'] = tiltx
      var tilty = bytesToInt(bytes.slice(11, 12)) / Math.pow(256, 1) * 4 - 2
      decoded['tilty'] = tilty
    }
  }
  return decoded
}

function bytesToInt (bytes) {
  var integer = 0
  for (var n = 0; n < bytes.length; n++) {
    integer += bytes[n]
    if (n < bytes.length - 1) {
      integer = integer << 8
    }
  }
  return integer
}

ttn_example.cpp

#include <TheThingsNetwork.h>
#include <private_keys.h> // imports appKey and appEUI from external file

#define loraSerial Serial1
#define freqPlan TTN_FP_EU868 // Use european freq plan
#define COUNT_OF(array) (sizeof(array) / sizeof(array[0])) // gets array size

TheThingsNetwork ttn(loraSerial, Serial, freqPlan);
bool is_connected = false;
uint8_t dataBuffer[12] = {0}; // uint8_t is byte, buffer can hold 12 bytes

void send_ttn_message(uint8_t* data, size_t data_size, port_t prt = 1) {
    if(is_connected){
      ttn.sendBytes(data, data_size);// sizeof(data)
    } else {
      Serial.print("ttn message: ");
      uint8_t i = 0;
      for (i = 0; i < data_size; i++){ // prints byte message in HEX encoding
        if (data[i] < 16) {
          Serial.print("0");
          Serial.print(data[i], HEX);
        } else {
          Serial.print(data[i], HEX);
        }
      }
      Serial.println("");
    }
}

void setup(){
  Serial.print("--- TTN STATUS ---"); ttn.showStatus();
  ttn.provision(appEui, appKey);
  is_connected = ttn.join(10); // try to connect up to 10 times 
  if (!is_connected){
    Serial.print("Join to TTN failed.");
  }
}

void loop(){
  // ...
  // Messaging the TTN Application
  if (iteration % send_per == 0){ // send only infrequently
    send_ttn_message(dataBuffer, COUNT_OF(dataBuffer));
  }
  // ...
}