GSM module as UART peripheral: sending SMS with GPS coords in case of emergency landing

[nzs001]

Goal: Flight controller to send the GPS coordinates in SMS using AT commands on UART to the preset phone number with the connected GMS module in case of emergency situation, landing etc. to support finding the lost aircraft.

Purpose: During waypoint mission or long range autonomous flight out of RX or VTX range the in case of emergency landing, finding the aircraft is hard. In GSM coverage area, with a smart phone it would be possible. If this UART feature would be coded in the FC no additional MC is needed to process telemetry data and to send AT commands to the GSM module

Implementation:
GSM module is connected directly to a UART port of the FC.
Emergency conditions to be defined and configured in INAV: emergency landing performed, 0 ground speed for a while, call received on the GSM module, etc.
SMS receiving phone number to be preset in INAV

If anyone is willing to make this a reality, I would be more than happy to test it!

Thanks,
Zsolt Nagy

[digitalentity]

We were just recently discussing such thing amongst core developers.

[wx4cb]

I already have a number of these devices around somewhere. if i can find one, i'll be willing to donate to the cause - obviously you'd need to supply your own sim card LOL

[digitalentity]

I purchased this device - https://www.aliexpress.com/item/mini-A6-GPRS-GSM-Kit-Wireless-Extension-Module-Board-Antenna-Tested-Worldwide-Store-for-SIM800L/32714639345.html

Adding GPS/GPRS functionality to INAV is a rather big project, so don't expect this to be implemented very fast

[wilco1967]

Would be a nice project, but keep in mind, as a lost model finder, it depends on the FC still 'alive' after the crash. It won't work if the battery got disconnected in the crash.

Some idea:
Perhaps some GSM modules exist, that have a possibility to connect a small battery (100mAh 1S or so), and can be programmed (by the FC, over a UART) to sent out an delayed SMS with the GPS coordinates after a delay of say 10 seconds.
If everything is still flying ok, have the FC cancel sending the SMS before the 10 seconds have expired, so it never actually gets send.
However, If the FC 'dies' (lost battery in a crash or so), or otherwise detects there is a problem, the GSM module would sent out the SMS, with the last 'good' GPS coordinates, using it's own battery power, once the 10seconds have expired (and it didn't get the command to cancel the last SMS).

If the FC is still happy and flying, it simply 'tells' the GSM module to forget about the last message, and prepare a new SMS, with new coordinates, to be sent 10 seconds later (which will also be cancelled before it actually gets send if everything is alright).

This would require a GSM module that can be programmed with a delay, and accepts cancelation of a SMS already prepared... don't know if something like that exists, but it would be a great feature...

kind of a tBeacon, but then using SMS / GSM.

[wx4cb]

If you were going to go with that complexity you might as well just use a small Arduino board with it that takes a a pwm input from the flight controller on a spare Channel.

when that disappears it just sends the GPS coordinates out.

I've actually done something similar vehicle tracking

[digitalentity]

Most GPS modules out there have pads for connecting a 1S LIPO.

Possibilities to use this feature:

1. Use GSM/GPRS to send telemetry to a user-defined web-service while FC is still alive
2. Use GSM to periodically send SMS messages on certain FC events

This is definitely not a proper replacement for lost model finder. An extension board that is smarter than FC and has it's own backup battery is a better solution, but no such board exist yet

[potater1]

Alright, I'm now testing a piece of GSM telemetry code that i added to INAV.
It sends you a text message with the GPS coords and other info and is able to respond to an incoming phone call.

I haven't been able to figure out the configuration system yet, so all settings for this are hard coded at the moment. If anybody can explain how the port configuration and CLI variables are handled, I can maybe get something usable done fairly quickly.

[giacomo892]

@potater1 nice work! You can check how to add a setting from another PR (like https://github.com/iNavFlight/inav/pull/3349/files for instance)

[digitalentity]

Nice! I have some GSM related code in the works, but it's far from being ready. If your code is already functional it might be worth improving it 😄

[potater1]

Well the port opening part wasn't too hard after all... the alpha version is now done. See the gsm branch in my repository.

It's very simple to use, no settings required except the port and the PIN on the sim card (it has to be 0000). You make a phone call to the module, and you get back a text message like this:

VBAT:0 ALT:0 DIST:0 SPEED:0 SATS:0 GSM:27 google.com/maps/@65.1231237,24.3213216,500m

the coordinates being given as a Google maps link.

[shellixyz]

@potater1 Nice !

You could just require the PIN protection to be disabled. It is just as good as requiring a 0000 PIN.
Why not waiting for a SMS instead of waiting for a call ?

[potater1]

Yeah didn't even think of disabling the PIN... it should work either way, I don't think the module minds it if you give it an unnecessary PIN.

Just calling the number may be quicker than sending a message, and it's free because the module doesn't answer the call. I'll add a text message receiving function if there's interest. I guess it would be for changing settings in mid flight?

[shellixyz]

In my country SMS are "free". I don't know any service subscription that doesn't allow the unlimited use of them. My idea was not to use them for changing settings but why not. The idea was only to use them to send a command/code instead of a call to prevent it from sending unwanted messages in case it receives an unwanted call/message.