I had always been looking for a way to use my app myself. So I came up with the idea to make the app operable with a button that I can press myself, for example a smooth-running one. But I had also thought of a blink switch, like Steve Hawking used. It's not a big technical challenge.
Since my app only needs four keypads, it should be much faster and easier than a conventional on-screen keyboard!
So I had thought about how I could implement such a control in the app. While searching I found by luck that Android already offers such a possibility. Precondition for this is at least Android 5.0 on the device. All you have to do is install the App Adroid Accessibel Suite (https://play.google.com/store/apps/details?id=com.google... ). An app directly from Google, which after the installation only leads to an addition in the settings of Android itself. In the settings, the ease of use is supplemented by some options and of course by the operation with one or more buttons.
It is possible to connect a button directly, a mouse is also possible if you can press one button.
It is also possible to use various buttons via Bluetooth. There are already finished smooth-running buttons like the "blue2", but they cost over 200 euros. It is enough a game console for few euro, like this, also at Amazon. These often have very smooth buttons, like a mouse. If not, no big bad investment, or something for the children. ;-)
I will perhaps present later also still another low-priced solution.
With the Switch Access operation you can also operate the phone and many other app's that are set up for this. Even the on-screen keyboard can be operated and you can surf the internet!
Good luck with the first operation!
How to set the parameters is described in many videos in different languages. Search for "Switch Access Android" here. Here is a link from Android directly.