LGT-92

Project LGT-92
Improving LGT-92 LoRaWAN tracker software
Status	Initializing
Contact	bertrik
Last Update	2021-08-10

What

This page is about the Dragino LGT-92, a GPS-enabled LoRaWAN tracker node.

The plan is to investigate if the firmware can be improved, e.g.:

• fix minor existing bugs
  • see the Issues page on github
• add Cayenne encoding
• collect information on how to interface with it (over the "USB" port)
• perhaps write a replacement firmware, that can be easily compiled with platformio

Hardware

As far as I understand:

• STM32L151 microcontroller, could also be STM32L072 I can't get this really clear
• GPS
• accelerometer, MPU9250?
• button, 3 LEDs (R, G, B)
• 1000 mAh battery + charging circuit

Information provided by Dragino: https://github.com/dragino/Lora/tree/master/LGT-92

Manual: https://www.dragino.com/downloads/downloads/LGT_92/

Software

• Dragino binary firmware downloads: https://www.dragino.com/downloads/downloads/LGT_92/firmware/
• Dragina source code: https://github.com/dragino/LGT-92_-LoRa_GPS_Tracker
• Decoder: https://www.dragino.com/downloads/index.php?dir=LGT_92/Decoder/

It's a bit peculiar that there are binary versions out there that have no correspondence to the source archive. Every commit in the official source archive consists of a huge number of changes, often includes also binary/intermediate files.

My fork of the Dragino firmware: https://github.com/bertrik/LGT-92_-LoRa_GPS_Tracker

Work in progress for an Arduino firmware: https://github.com/bertrik/lgt92

Flashing

When holding the reset pin (e.g. push a dupont-pin in the hole next to the USB connector), you can communicate over SWCLK/SWDIO debug pins.

ST-Link pin connections (from: https://github.com/dragino/LGT-92_-LoRa_GPS_Tracker/issues/10):

 ST-LINK v2 5.0v  <--> Dupont red pin
 ST-LINK v2 SWDIO <--> Dupont white pin
 ST-LINK v2 SWCLK <--> Dupont green pin
 ST-LINK v2 GND   <--> Dupont black pin

Official firmware binaries are available here

For example:

 openocd -s /usr/share/openocd/scripts -f interface/stlink.cfg -f target/stm32l0.cfg

To program a HEX file:

 openocd -s /usr/share/openocd/scripts -f interface/stlink.cfg -f target/stm32l0.cfg -c init -c "program LGT92-EU868-v1.6.2.hex verify reset exit"

This takes only a few seconds.

TTN mapper configuration

Connect it at 9600 baud through a USB-UART converter, pins GND, RX, TX. Switch the LGT-92 on.

 USB serial TXD <--> Dupont white pin
 USB serial RXD <--> Dupont green pin
 USB serial GND <--> Dupont black pin

To reset settings after a firmware update

 AT+FDR

Run these commands to set it up with ABP keys, ADR off, uplink at SF7 every 15 seconds:

 AT+NJM=0
 AT+ADR=0
 AT+CFM=0
 AT+DR=5
 AT+LON=1
 AT+MD=0
 AT+DADDR=26 01 1A 30
 AT+NWKSKEY=FB 09 6B 85 86 AF 47 12 E8 AE 67 CB 7F A9 CB 51
 AT+APPSKEY=CB 9B 8F F5 E6 2C 8E 87 9E 0B 6B 1F 4B 69 14 FA
 AT+TDC=15000
 AT+NMEA886=2
 AT+PORT=1
 AT+FTIME=0
 AT+PDOP=10.0
 AT+SGM=0

The AT+SGM=0 line allows the altitude and HDOP to be sent.