'Serial USB Terminal' is a line-oriented terminal / console app for microcontrollers, arduinos and other devices with a serial / UART interface connected with a USB to serial converter to your android device. 

This app supports USB to serial converters based on
- FTDI FT232, FT2232, ...
- Prolific PL2303
- Silabs CP2102, CP2105, ...
- Qinheng CH340, CH341
and devices implementing the USB CDC protocol like
- Arduino using ATmega32U4
- Digispark using V-USB software USB
- BBC micro:bit using ARM mbed DAPLink firmware

To connect USB to serial converters, your android device must support USB OTG aka. USB host mode. Most devices support this today, but in case of issues check with one of the various USB test apps, if host mode is enabled in your android kernel.

All features in this app are free. In-App purchase is only used for the 'Donate' option.

Looking for source code? Here you find a simplified variant of this app:
https://github.com/kai-morich/SimpleUsbTerminal

Terminal for serial devices connected with USB to serial converter