TELEMETRY Plane->Ground station

Hey there! So this past year I've been diving ever deeper into the world of long range fpv on fixed wing UAV platforms and I'm ready to start on a new ground station project that is to include a high gain antenna with tracking capability. The plane has a GPS onboard and I plan on using Latitude and Longitude as well as the reading from the borometer to simulate the plane's position of a flat 3D coordinate plane, while using the init position when the plane is powered on (next to ground station) as the home reference point. Having these two points, it's just a matter of some simple math to determine with a good deal of accuracy where the antenna tracker needs to be orientated.

The problem that I'm running into is determining how to go about getting that GPS and telemetry data from the aircraft back to the ground station. The most promising solution seems to be using the audio line of the video transmitter onboard the plane, as the tracker on the ground will be receiving it and is the piece of equipment that needs the data to track. My question is, can I feed a digital signal through the audio line of the VTX on the plane and get a digital signal back on the other side? Or do I need to convert digital to analog plane side and covert back to digital on the ground? If you guys have any ideas, I would much appreciate it. :slight_smile:

As a side note, I'm aware that there are commercial solutions for sending telemetry to ground station. I'm trying to avoid broadcasting a 3rd frequency from the plane to avoid interference, and If I can get this working using an Arduino or ARM controller, I'm allowed that much more freedom to fiddle with the program later and implement new features later.

Tyler_Jwll:
As a side note, I'm aware that there are commercial solutions for sending telemetry to ground station. I'm trying to avoid broadcasting a 3rd frequency from the plane to avoid interference

As long as you have decent distance between your receiver and telemetry transmitter (in BOTH physical location on the plane and in terms of frequency), you shouldn't have a problem with interference.

I build Arduino RC airplanes myself and have been able to report plane telemetry (including GPS coordinates, altitude, etc) back to my ground station. Here's a link to my latest build-log, which you might be interested in. I was able to do it by using 3 sets of radios:

  • Command and control: 915MHz 3DR radios
  • FPV: 5.8GHz radios
  • Telemetry: 2.4GHz XBee radios

Using this radio array, I used this library to reliably transfer the telemetry to the ground station for processing.

And here is a link to the library I wrote for Arduino RC plane control. It includes the complete code for collecting and reporting telemetry to the hand-controller/ground station.

Thank you for your reply and links, I'll definitely check out the libraries and build log. I've considered using a third radio for telemetry as I said before, but thought it might be a cleaner setup using the audio line of the VTX if it's possible without too much headache.

For radio systems right now I'm using FRsky's 900MHz module for the handheld TX, and I've recently made the switch over to the 1.3GHz VTX from ReadyMadeRC. Beforehand, I had been using 5.8, but I couldn't seem to push past the 7 mile mark flying over the ocean without losing video. I've heard that even with low pass filters and other safeguards, it's troublesome running 1.3 and 5.8 on the same platform due to harmonics. If I end up hitting a dead end trying to use the audio line for data, I may see about trying to find a 433MHz telemetry module. I just finished spotwelding up a LiIon pack and am looking to really push the envelope on distance in the coming weeks.

3.) Implement and test various autopilot features in a simulated environment (Processor-In-Loop Simulation) using an Arduino with the popular computer game War Thunder. This will allow me to test, debug, and develop autopilot logic before implementing it on my plane. I’d rather catch the bugs in a simulation before it crashes my real RC plane.

Arduino Scratch Build - "Screamin' Seagull II" | FliteTest Forum

I had no idea this was possible. Definitely interesting, haha. I’ve sure put a few hours into this game.

Tyler_Jwll:
I had no idea this was possible. Definitely interesting, haha. I've sure put a few hours into this game.

Yeah, if you use a Teensy 3.5 or 3.6 as an HID gamepad device, you can run "flight control software" that interacts with the game. The feedback comes in the form of a Python or C++ program that reads in game vehicle telemetry from War Thunder's localhost running on your PC. The Python/C++ program then reports the telemetry back to the Teensy via USB.

It works, but be sure not to implement it in any competitive match - it's only for research and there's no need to get banned over it! lol

What your atempting to do is really very trivial with LoRa, it has a range capabilty of several hundreds of kilometers on simple omni antennas.

But in a lot of places in the world flying a RC plane beyong unaided line of sight is illegal.

Tyler_Jwll:
Thank you for your reply and links, I'll definitely check out the libraries and build log. I've considered using a third radio for telemetry as I said before, but thought it might be a cleaner setup using the audio line of the VTX if it's possible without too much headache.

I doubt it'll be possible to get much out of the audio line. I imagine you'd sever the audio line and attach it to the Arduino's UART port (on both plane and ground station)? Either way, I imagine the audio line has a 20KHz low pass filter, which could possible degrade any digital communication.

It might work, however, if you use a really low baud...

Power_Broker:
I doubt it’ll be possible to get much out of the audio line. I imagine you’d sever the audio line and attach it to the Arduino’s UART port (on both plane and ground station)? Either way, I imagine the audio line has a 20KHz low pass filter, which could possible degrade any digital communication.

It might work, however, if you use a really low baud…

I was thinking at worst case scenario I would have to use a microcontroller that’s equiped with a DAC to get it to pass through the audio line unhindered. I know the Blue pill is capable of it. It went be a terrible amount of data, and the most important portion is the GPS coordinates which updates at 10Hz.

srnet:
What your atempting to do is really very trivial with LoRa, it has a range capabilty of several hundreds of kilometers on simple omni antennas.

I did a bit of researching on LoRa a year or so ago when I was working on a DIY handheld TX. At the time I was looking to choose a radio system that would be capable of sending control commands and receiving telemetry and the LoRa modules I came across wouldn't have been able to process the data quickly enough. That could be something to look into as a solution to this problem though.

What if I rigged up an Arduino to send the data to the audio line using a frequency within the range the VTX would pass. If it wouldn't accept a square wave, I could break out the oscilloscope it and tune it with a ceramic capacitor to get the shape of a sine wave. Then just send it as ASCII one byte at a time

It sounds like you just re-invented the modem (MODulator + DEModulator.)

APRS stands for Automated Packet Radio System. Those guys were sending data over amateur voice radios in the 1980s. You could probably modify one of those modems to work on your video's audio channel.

I've used APRS on off-the-shelf amateur radios for more than 100km aircraft-to-ground telemetry.

MorganS:
It sounds like you just re-invented the modem (MODulator + DEModulator.)

I’ve used APRS on off-the-shelf amateur radios for more than 100km aircraft-to-ground telemetry.

I’m going to have to look into this. It sounds promising. The APRS that you use sounds like it’s almost plug and play. Feed digital data into it, it sends modulated signal out then it’s reversed on the ground?

@MorganS

Could you link an example of the APRS you use?

I bought integrated modems and radios, so it was like a very long RS232 cable for me. Not relevant for your usage.

Tyler_Jwll:
the LoRa modules I came across wouldn't have been able to process the data quickly enough. That could be something to look into as a solution to this problem though.

Perhaps include the required data rate in the original post, if its a critical item. Saves people writing up solutions for you that are not fast enough.