I need a small, headless Android service that recognises a CH340-based USB-to-RS232 converter on devices running Android 7.0 or later, opens the serial port at 9600 baud, transmits the single byte 0x55 (55H) once, then waits for and logs any reply that arrives. Interface No user interface is required; the app can run silently in the background and write its status and any received bytes to Logcat. A simple on-screen notification on connection or completion is acceptable but not mandatory. Testing scope For now I will validate the APK on one specific handset that I will supply during acceptance, so extensive multi-device support is not necessary. Please keep the code portable enough for future expansion. Error handling I only need solid handling of data-level problems—CRC / framing / mismatched byte counts, etc.—with clear log messages. Connection failures can surface as standard Android USB errors. Deliverables • Signed installable APK • Clean Android Studio project (Java or Kotlin, API 24+) using the standard USB Host API or a proven open-source CH340 driver • Brief README covering build steps and how to interpret the logs Acceptance will be based on the app successfully sending 0x55 and echo-logging any response through the CH340 cable on my test device without crashing, plus clear logging of simulated data-error scenarios.