Link Telemetry - Version v1.0 "Odyssey"

University of Maryland Space Systems Lab Code written by Nicholas Rossomando

Link Telemetry (Link-TLM) is designed to be an integrated solution for tracking high-altitude weather balloons via the APRS network. The software interfaces with a Kenwood TM-D710GA radio via a RS-232 serial connection to recieve APRS packets. These packets are then decoded to yield location information throughout the flight.

Link-TLM is designed for and developed on Linux machines. It should compile on any properly configured Linux distribution. However, it will not compile or run on Windows. It may compile and run on OSX, but this has never been attempted or tested, and so is not considered supported (and may not work at all).

The software is currently nearing feature-completion. It currently recieves packets from the radio, parses them, logs them, and calculates several dervied values including vertical and horizontal speed and downrange distance. Output is provided via the terminal, and will also be exported to a live-updating JSON file for other processes to access in the future. Link-TLM has been used in its various versions to track about 15 of the University of Maryland Nearspace Program's high altitude balloon flights and is now a standard part of the tracking setup.

Dependencies

Link Telemetry's external dependencies are g++ 5.0 or higher, GNU make, and the RapidJson library. RapidJson is provided with the software (along with a copy of its license; it is MIT, the same as Link-TLM itself). G++ and GNU make are usually found in a development package for a given distribution; for Debian-based distributions they are found in build-essential, and in Arch they are found in base-devel (likely already installed). However, these packages may not install the latest version of g++. To check what version is installed, run g++ --version. If the version is less than 5.0, as in Linux Mint 17.3, it may be possible to install a newer version of the compiler. For Mint:

sudo add-apt-repository ppa:ubuntu-toolchain-r/test
sudo apt-get update
sudo apt-get install g++-5

In this case, the makefile handles choosing which compiler alias to use.

Building

Building the code is simple thanks to GNU make. Simply open a commmand line, navigate to the Link-TLM directory, and run the command make. If multiple cores are available, the build can be sped up by running make -j $NUM_THREADS, i.e. make -j 4 to use 4 threads.

In order to build the Link-TLM testing code, instead run make test.

To clean up extra files created during compilation, run make clean. Logs can be purged by make logclean, and the executables themselves can be removed by make purge.

Configuring

There are two configuration files for Link-TLM, located in the Prefs subdirectory. settings.json controls overall application settings, while regex.json defines the regular expressions used to extract data from recieved APRS packets.

settings.json

• balloonCallsigns: Array of strings; each string is a callsign for a tracker that stays with the balloon for the whole flight (including SSID)
  • Set to 0 (not in array) if no callsigns defined
• vanCallsigns: Array of strings; each string is a callsign used in one of the chase vans (including SSID)
  • Set to 0 (not in array) if no callsigns defined
• droppedPayloadCallsigns: Reserved. Not yet implemented.
• unparsedLogFilename: Filename/path for log file of all packets recieved by radio. Raw text file output.
  • Set to empty string ("") if unused. Defaults to Logs/unparsedPackets.txt.
• parsedLogFilename: Filename/path for log file of packets parsed by radio. Outputs as CSV, currently with extra timestamp.
  • Set to empty string ("") if unused. Defaults to Logs/parsedPackets.txt.
• jsonLogFilename: Filename/path for live JSON file output.
  • Set to empty string ("") if unused. Defaults to Logs/jsonOutput.json.
• kmlLogFilename: Filename/path for live KML file output.
  • Set to empty string ("") if unused. Defaults to Logs/kmlOutput.kml.

regex.json

NOTE: All special characters must be escaped in this file. Currently, that involves doubling all backslashes (i.e. \d becomes \\d)
NOTE: All fields must contain a valid regular expression

• callsignPattern: Used to extract radio callsign
• timestampPattern: Used to look for a timestamp and extract it if it exists
  • NOTE: If no timestamp in packet, the time the packet was recieved is used instead.
  • NOTE: Current BPP trackers do not output timestamps.
• compressedLatLonPattern: Used to search for latitude/longitude in APRS compressed format and extract it if it exists
  • NOTE: Output will be fed to decompressor for APRS format only. MIC-E will not be interpreted properly.
• uncompressedLatPattern: Used to search for uncompressed latitude data and extract it if it exists
• uncompressedLonPattern: Used to search for uncompressed longitude data and extract it if it exists
• altitudePattern: Used to extract altitude data
• uncompressedCseSpdPattern: Used to check for and extract course/speed if uncompressed
• compressedCseSpdPattern: Used to check for and extract course/speed if compressed
  • NOTE: It is possible (and perfectly valid) for neither of the above Cse/Spd fields to exist in an APRS packet
• uncompressedCommentPattern: Used to extract comment from packets that had compressed data
• compressedCommentPattern: Used to extract comment from packets that had uncompressed data

Running

To run the program after building, simply run ./Link-TLM from a command line in the Link_TLM directory. Enter the filename of the serial port you are using when prompted (something like /dev/ttyUSB0). A radio is not technically necessary; any serial device outputting APRS packets will work. For testing without a radio, an Arduino writing APRS packets captured on previous launches is used. Output to the screen can be monitored, and output is also saved to two log files. The log filenames are specified in settings.json in the Prefs/ subdirectory.

Background Info

Why Develop This?

The current state of APRS software is fairly poor. None of the software we found were quite able to meet the Balloon Payload Program's needs. Most significantly, all options avaiable required an internet connection, which we rarely have while chasing the balloon. Additionally, very few had options for directly interfacing with a radio; instead, they collect their information from websites like APRS.fi. Thus, an in-house solution was decided upon.

Forward Path

Link-TLM is nearly feature complete in its current state. Due to several advances in the Nearspace program, we no longer need a full-fledged mapping solution. Additionally, the always-buggy embedded Python has been stripped out of the application and replaced with pure C++. This was facilitated by the improvement and widespread compiler support for C++11's built in regular expressions. Graphing using matplotlib will be replaced by an external graphing implementation using COSMOS, which is already in use as a ground station in our tracking setup.

Remaining tasks:

• Implement non-buggy and non-hacky dropped payload tracking
• Implement chase van tracking
• Revisit and improve radio serial interface

Link-TLM has been bumped to version 1.0; these few remaining features are not considered critical to the software's usage, and thus Link-TLM is considered, finally, released! However, development will continue to include these features.