USB to DB9 Adapter Back-to-back RS232 Serial Com Port Docker Pi 3V you can bridge the

3V you can bridge the solder jumper next to the voltage regulator to bypass the regulator (refer to schematic link below)

electret microphone

measured data will be stable

RAK811 Breakout Module Datasheet

you have a complete set of tools learning this tiny computer and exploring amazing applications you can do with it

USB to DB9 Adapter Back-to-back RS232 Serial Com Port Docker Pi 3V you can bridge theThe USB to RS232 serial port adapter provides the connection between USB and the traditional RS232 serial port. The adapter is designed for connections to cellular phone, PDA, digital cameras, modems, or ISDN terminal adapters through your USB port. Since the adapter uses no IRQs, it is perfect for you to connect your serial devices attached to your PC. And there comes with a useful USB extension cable. USB specification 2. 0 compliant Supports RS232