Please try the Android App built with usbserial4a on Google Play: [PyTool USB Serial Free](https://play.google.com/store/apps/details?id=com.quanlin.pytoolusbserialfree), [PyTool Modbus Free](https://play.google.com/store/apps/details?id=com.quanlin.pytoolmodbusfree).
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Get Pydroid Apps from [here](https://github.com/jacklinquan/Pydroid_Apks), or get the latest versions on [Google Play](https://play.google.com/store/apps).
Open `example.py` and run it. When it runs for the first time, it might prompt you for permission to access the USB device. Accept the permission and run this script again, then it should send the data `b'Hello world!'` as expected.
Go to `Menu->Graphical program output`.
Scroll to the last line, it should list all the USB devices connected to the Android phone/tablet with vendor id, vendor name, product id and product name.