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Вам понадобится как минимум один RN4020 модуль, телефон с Android, TTL to USB Serial converter (например, TTL-232R-3V3 - FTDI),
источник 3,3V и компьютер.
1. Connect Pins 23 (VDD), 15 (Wake_hw) and 7 (wake_sw) to 3,3V
    Get the 3,3 through a Voltage divider from the 5V from the TTL-Rs232-3V3 Vout or from a 3.3V external source
    (like a battery or something). Do NOT connect the RN4020 to +5V. 
2. Connect Pin 1 (GND) to 0V
3. Connect Rx, Tx, CTS, RTS and GND to your TTL-Rs232-3V3 converter.
4. Plug in everything
5. In Windows open "CoolTerm" (or which Terminal software you like) and connect
    to the comport (115200, 8N1, Hardware flow control (CTS))
6. If you reboot your RN4020, you should get "CMD" in the Terminal, meaning
    you are in command mode
7. write "+" (and enter key) into terminal to activate echo on
    It should respond "Echo On"
8. write "sr,32000000"
    It should respond "AOK"
9. write "r,1" to reboot
    It shold respond "Reboot" and then "CMD"
10. Install "MLDPTerminal8.apk" App on your Android phone. You can download the app from  
     under Demo Software -> MLDP Demo for Android
11. (Maybe optional) The first time only, open bluetooth settings on your phone and add the new device
      The peer passcode appears in the Terminal software on your PC. 
12. Open the "MLDP Terminal" on your phone, connect and type some characters in the Outgoing field. You should get 
      them in your PC Terminal Software. It should first Show MLDP, then the chars.
      If you want to send only chars from PC to the phone, start with "I" to enter in MLDP mode.
13. Now write anything in the PC Terminal Software, and in goes to the Incoming field in your Phone.
OBS: Its really recommend to use the Hardware flow control. But it will work also pulling CTS and RTS with  resistors to ground.

Ниже аппнот по соединению двух микроконтроллеров между собой с помощью этого чипа:

Also look:
Realted github: