Lilygo T-Echo with XCnav

[Janos Bauer]

Dear Group members,

I'm wondering if anyone is using a direct USB connection setup between XCNav (or any other XCSoar-based system) and T-Echo for power supply and NMEA communication. Is this theoretically feasible? I know a Bluetooth connection should work, but I would prefer more robust wired communication.

Additionally, it would be helpful to see a range analysis with T-Echo or similar devices to compare their performance against original Flarm or PowerFlarm units.

Thanks for your help.

Regards,

Janos

[Moshe Braner]

Welcome Janos!

Go ahead and try a USB connection!  SoftRF does offer the ability to send the NMEA output to the USB port, on either the T-Beam or the T-Echo.  The other end of that cable I am not familiar with.  I use a computer (Windows or Linux) on the other end, for debugging.  In the air, you would want to use a phone or tablet device.  If that device can work as a USB host (via "OTG"?) then that may be possible.  But does software like XCnav offer the USB port as an available data source in its configuration?  I know I used USB OTG (via a Y-cable for external power connection) to get data from a USB GPS "puck" into Tophat (a fork of XCsoar) years ago.  That OTG connection should have worked with SoftRF too, I should try that again!  (SoftRF did not exist back then.)  But, I found that the USB connection mysteriously dropped once in a while, and I had to reboot Tophat during the flight.  Only once I set up a serial connection instead (to a TTL-serial GNSS puck, and later to a FLARM) did I get a reliable system.  But the USB dropouts may be the fault of Tophat or of the Android 2.x running in the Nook e-reader I used it on.  You phone or tablet may work better.  Also note that the T-Echo uses "USB CDC" which is a different way to make a USB connection look like a serial connection to the software, and your phone's OTG may or may not work with that.  Let us know!

Regarding range, I've read claims that the T-Echo's range is shorter than the T-Beam.  The antenna it comes with looks pretty but is not a good antenna.  It does have an SMA connector so you can try other antennas. Also there are claims that it transmits at a lower power than the T-Beam, although I don't see that in the source code.  In the USA the legally allowed power is higher than in Europe, so SoftRF transmits at a somewhat higher power than FLARM, and appears to have a slightly longer range therefore.  "Range" can also mean reception range, and that is what the FLARM range tool shows you, unlike the OGN station reports.  That range would depend on the antenna and on the receiver design.  The T-Echo uses an sx1262 radio chip, which is supposed to be a bit better than the sx1276 that is in most T-Beams.  The T-Echo also seems to have better GNSS reception sensitivity than the T-Beam has with the poor GNSS antenna that it comes with.  But you can replace that antenna on the T-Beam with a better one.

[Janos Bauer]

Thanks Moshe for the encouragement. The targeted host device is this:  https://xcvario.com/product/xctouchnav/

On one of the product pages I managed to see a promising example and even consulted with the manufacturer about this setup. He mentioned a GPS connector app on the Android host site which secured the communication. So there is a good chance to succeed with this T-Echo SoftRf device as well as an external Flarm NMEA source.

Regards,

Janos

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[Moshe Braner]

Interesting.  So you are using the XCnav on its own, without an XCvario?  (Otherwise it would perhaps be better to feed the data from SoftRF to the XCvario so it can compute wind and also show FLARM warnings - although the XCnav may do those things too.)  What does the "GPS connector app" do?  Your photo shows a USB GPS stick plugged into the XCnav - if that works, then plugging the T-Echo in there should work too?  Will the XCnav also know how to process the FLARM sentences (PFLAA, PFLAU) and display the traffic on the map?

[Janos Bauer]

Unfortunately XCvario does not support Flarm NMEA over BT. I plan to use XCvario, hopefully TouchNav can forward the NMEA flow, so wind calculation and other features might work on XCVario.

Yes, XCSoar what runs on TouchNav does process Flarm NMEA, even radar and navigation to Flarm target is feasible.

I assume the GPS connector app creates the virtual serial interface from the USB port.

Janó

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[Moshe Braner]

Ah, you are actually running XCsoar, just on the XCnav hardware. OK.

Are you sure "XCvario does not support Flarm NMEA over BT"?  All its data routes are bidirectional.  I know that the XCvario supports GPS+FLARM input via WiFi.  And I added some WiFi capabilities to SoftRF to make that possible (TCP client mode).  If you do that, UDP output from SoftRF magically gets through the WiFi mini-router inside the XCvario and appears in XCsoar.  No cables needed for either connection!  For more data routing flexibility, use my version of the XCvario firmware (which also has many other improvements).  https://github.com/moshe-braner/XCVario  I am still working on the Xcvario firmware, next thing in the pipeline is wind estimation without circling and without a compass module but with TAS data from the XCvario's pitot, static and OAT sensors.

[Moshe Braner]

Also note that the XC nav touch has RJ45 connectors.  If using a T-Beam (rather than a T-Echo) can use an RJ45 serial connection instead of using the USB jack with its various problems - but would need to add some serial wiring to the T-Beam.  But if you want to keep using a T-Echo (or an unmodified T-Beam) the USB connection may work well enough.  Let us know how well it works for you!

[Janos Bauer]

Mmm, that is interesting. I shall try this wifi mode once all the gadgets are on my table. Thanks for the hint.

Accurate wind calculation without circling and compass module? Sounds like mission impossible, but I might miss a tricky path of logic;)

Jano

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[Moshe Braner]

It is possible if you sample multiple directions of travel and combine the data.  XCsoar tries to do that with just GPS data, I hear that does not work very well.  In XCvario, I also have an estimate of TAS (but no heading, without a compass).  That makes it easier.  It seems to work in simulations I am doing.  It works in an ILEC SN10 vario (designed in 1998), but I don't know what its algorithm is.

[Janos Bauer]

Aha, that method might work, but sample variation might kick in.

You might consult with Dave Nadler, developer os SN10 software:

https://youtu.be/YpA_9nSjFdA?si=dlDq3tFliu_5ZbNd

Regards,

Jano

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