Can Android connect over serial?

[JonasVautherin]

Asked on Slack, copying here for the record:

Hello!

Just wanted to know whats the best way to create a custom android groundstation app with mavsdk? There doesn't seem to be any framework for connecting to a serial connection on android to a telemetry module. I tried modifying the qgroundcontrol app but it isn't java based so it doesn't work for my purposes. I also tried using dronekit but their code is so old, much of it is unsupported by android studio, same story with trying to fork Android Tower.

Thanks in advance!

[JonasVautherin]

MAVSDK-Java will always look like "pure Java" to you, because we hide the C++ stuff 😄. Once the C++ will be packaged into an Android library, you will just have to do something like:

startMavlink(<connectionUrl>);
Action action = new Action();
action.arm().andThen(action.takeoff()).subscribe();

And the drone will takeoff. With connectionUrl being something like udp://:14540.

Before that (i.e. right now), you will have to run mavsdk_server on your computer (you'll find binaries in the "assets" for different platforms on the release page), and the code will look like:

Action action = new Action(<ipOfYourComputer>);
action.arm().andThen(action.takeoff()).subscribe();

You see here that the first line (that would start mavsdk_server on your phone) is missing, because you run mavsdk_server on your computer instead. And also, you enter an IP in new Action(...), because you need to tell the SDK where to contact mavsdk_server (default is 'localhost').

This means that you can totally develop your app with the current SDK, but your app has to connect to your computer (with <ipOfYourComputer> as described above), and your computer has to connect to the drone (or simulator). When we release mavsdk_server for Android, it will be a matter of adding the startMavlink() line and your app will run completely on your phone 👍.

Also, note that the Android wrappers are not super mature yet, but they are already quite advanced. So feel free to report bugs and to contribute fixes! Please get started with the java-client example!

[LorenzMeier]

@JonasVautherin The question was specifically around how you get the serial port of Android into an application. So what would help this user is if MAVSDK included the logic to open and read the UART: https://developer.android.com/things/sdk/pio/uart

From previous experience the simplest approach might be to read it in Java, push the payload down to C++ (mavsdk core) and then have the same flow as in C++.

This library kind of does this: https://github.com/chzhong/serial-android

[JonasVautherin]

Right, I missed that, and I was mainly hoping to actually move the discussion here.

I'm not sure we even need to add a new library. The app would definitely need the permission:

<uses-permission android:name="com.google.android.things.permission.USE_PERIPHERAL_IO" />

And then I wouldn't be surprised if mavsdk_server could "just" use it, given it has the right connection_url. Anyway I've been using that in the past, both from Tower or with proprietary software, and I'm sure there is a way.

It is probably not so difficult to try, but for that one would need to run the example first, as described above.

[maxwelllwang]

Would this help?
https://github.com/DroidPlanner/usb-serial-for-android/tree/develop/UsbSerialLibrary
if i "loaded" the mavsdk_server onboard the android app by just putting the mavsdk C++ library onboard? I could use these series of drivers.
Sorry if I am completely misunderstanding the functions I'm still relatively new to this

[JonasVautherin]

The serial connection would be done by mavsdk_server. Currently, that is done in serial_connection there. On Linux we would do something like:

./mavsdk_server serial:///dev/ttyUSB0

And my question would be: could we get that kind of address from Android (in Java), and would that be enough to access it (together with the permission mentioned above)?

I will try to have a look at that ASAP, but I would love your input on it!

[dunifi91]

Hi

First of all I would like to say it is really cool that there is a Java frontend implementation to MAVSDK 👍.
You said:

When we release mavsdk_server for Android, it will be a matter of adding the startMavlink() line and your app will run completely on your phone

Is someone working on it right now and will it come out soon or can it still take a long time? Because I have no idea how to program a serial connection on Android.

[JonasVautherin]

Hello @dunifi91!

I am currently looking into that 🙂. If everything goes well, it may work in a few days! Otherwise, at least I'll be able to tell you what I tried that doesn't work 😆.

[dunifi91]

Sounds good. I am looking forward to your results 🙂

[mirkix]

Hi @JonasVautherin Jonas, I am interested in using the MAVSDK-Java for an Android App as well. Is there further progress with the mavsdk_server running on Android, or is there any timeline when it will be available? Thanks in advanced!

[JonasVautherin]

Hej! Sorry I've been pretty busy these days. I have a proof of concept running mavsdk_server on Android, I need to wrap it up and push it. And then I'll need help to test the serial stuff. Sorry for the delay, I'll try hard to get that out next week!

[mirkix]

@JonasVautherin Thanks for the fast reply. We can do some testing of the mavsdk_server for Android if the server is available.

[JonasVautherin]

I pushed my changes, it is working (at least for me) with the android example app. Here is what I changed there, with link to the relevant code:

• Add io.mavsdk:mavsdk-server:0.1.1 to the dependencies.
• Start mavsdk_server in a background thread.

This is not the final version (I'd like to expose it through RxJava, and we should be able to stop mavsdk_server from the app as well), but that's already something.

Why does it concern this issue?

You can pass the connection url to mavsdk_server. Here I pass udp://:14540, but for trying a serial connection, that may be something like serial:///dev/bus/usb/001/002. And probably the app would need some more permissions.

I won't have time to try the serial connection in the next days, so please let me know here if you make tests! Also if the udp connection works.

Note:

The library only supports arm64-v8a (I published mavsdk-server with libmavsdk_server.so here). I hope it's enough for you to test for the moment!

[mirkix]

@JonasVautherin Thanks for pushing your changes. At the moment stuck at mavsdk-server on Linux because we want to use it with ArduPilot.