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LTM-lua

Introduction

This project provides an OpenTX LUA script that outputs LTM (inav's Lightweight Tememetry) on a serial port on an OpenTX radio.

Typical use case:

  • Radiomaster TX16S radio (which has two normal / not inverted UARTS)
  • Bluetooth module attached to a radio UART
  • LTM aware ground station mwp, ezgui, "mission planner for inav"
  • Antenna tracker that uses LTM.

Installation and Usage

  • Copy the script ltm.lua to the `SCRIPTS/FUNCTIONS' directory
  • Create a directory, SCRIPTS/FUNCTIONS/LTM; copy the files LTM/crsf.lua and LTM/config.lua to that directory, such that the following directory structure is maintained.
    ├── SCRIPTS
    │   ├── FUNCTIONS
    │   │   ├── ltm.lua
    │   │   ├── LTM
    │   │   │   ├── crsf.lua
    │   │   │   ├── config.lua
  • Enable the script as a Global Function or model specific Special Function.

Note that any Zip files in the release area will profile this directory structure.

The script may be invoked either on an external stimulus e.g. Telemetry or on a switch. See the OpenTX / TX vendor documentation for details on configuring your radio.

Note that the UARTs on the TX16S default to 115200 bps, so set BT devices accordingly.

Note also that in OTX 2.3.9, a bug causes no power to be supplied to the TX16S UARTS; this is fixed in the 2.3.10 nightlies.

Configuration

There are a few user editable settings in the file LTM/config.lua; currently the user must edit this file directly as no radio UI is provdied.

In particular, the onlyTracker setting may be used to provide only GPS data for antenna trackers. See the comments in LTM/config.lua for details.

Audio

The audio directory contains two synthesised voice files, ltmon.wav and ltmoff.wav that may be placed in SOUNDS/en and used to provide audible indications (via Special Functions) that LTM forwarding is enabled / disabled.

Logging

If the variable LOGGER is set to true, LTM binary messages written to a LOG/ file (simulator and radio). It is not advised to do this on the radio.

In the simulator human readable debug messages are generated unconditionally.

Caveats

Tested on a Radiomaster TX16S with OpenTX 2.3.9 (and 2.3.10 nightlies), internal module. Requires smartport (e.g. Frsky D16) compatible RX on the aircraft.

The scripts have also been tested using Crossfire with Taranis x9D+se, OpenTX 2.3 +luac, full Crossfire TX, Nano RX and the u360gts antenna tracker.

Other OpenTX compatible radios and other RX radio systems (e.g. R9) are NOT tested and as I don't have such hardware, may not work.

Copyright and Licence

(c) Jonathan Hudson 2020

GPL Version 3 or later.