Intro

This is a simple sketch demonstrating the capability of the TTGO T-Beam as a TTN Mapper Node on The Things Network LoraWAN.

Software dependencies

Arduino IDE ESP32 extension

TinyGPS++

MCCI-LMIC-Arduino : edit lmic_project_config.h for your own settings

Instructions

You need to connect the T-Beam DIO1 pin marked Lora1 to the pin 33 - So that the ESP32 can read that output from the Lora module. Optionally you can also connect the Lora2 output to GPIO 32, but this is not needed here.

You can program the T-Beam using the Arduino ESP32 board 'Heltec_WIFI_LoRa_32'.

TTN Console settings

On The Things Network side, the settings needed are available here.

To decode the binary payload, you can use the following javascript decoder function. Place code in TTN console payload formats.

  function Decoder(bytes, port) {
  // Decode an uplink message from a buffer (array) of bytes to an object of fields.
  var decoded = {};
  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;
  }

Todolist

• Save and reload the frame counter somewhere - GPS RTC data ? SPIFFS ? EEPROM ? - so I can check the "Frame Counter Checks" box as recommended on TTN.
• Also save the GPS 'status' so that on next boot it gets a fix faster.
• Switch to OTAA auth method for TTN and save the 'credentials' for reboot use.
• Reduce the power needed ! That thing is a power hog currently, we need to make it sleep most of the time as possible.
• Adapt the data send frequency based on current velocity : When not moving, an update per hour should be enough.

Let me know if you think anything else would make sense for a TTN mapper node : Open an issue, I will consider it.