Bluetooth 4.2 Module JDY-18

/*
  JDY-18 BLE module test on Arduino Uno

  Board: Arduino Uno (Tools > Board > Arduino AVR Boards > Arduino Uno)
  Board package: Arduino AVR Boards (comes with the Arduino IDE)
  Libraries: SoftwareSerial (included in the Arduino IDE), nothing to install

  Wiring:
    JDY-18 VCC -> Arduino 3.3V (never 5V)
    JDY-18 GND -> Arduino GND
    JDY-18 TXD -> Arduino D2 (SoftwareSerial RX)
    JDY-18 RXD -> R2 2 kOhm to GND, and R1 1 kOhm to Arduino D3 (SoftwareSerial TX)
    The R1 / R2 divider lowers the 5 V of D3 to about 3.3 V for the module.

  Serial Monitor: 9600 baud, line ending "Both NL & CR".
*/

#include <SoftwareSerial.h>

const byte BT_RX_PIN = 2;  // Arduino receives here (connected to module TXD)
const byte BT_TX_PIN = 3;  // Arduino transmits here (to module RXD via divider)

SoftwareSerial bt(BT_RX_PIN, BT_TX_PIN);  // Software serial port for the module

// Sends one AT command and prints the answer on the Serial Monitor
void sendCommand(const char *command) {
  Serial.print("> ");
  Serial.println(command);

  // Throw away any old data in the receive buffer
  while (bt.available()) {
    bt.read();
  }

  // The module needs every AT command to end with \r\n
  bt.print(command);
  bt.print("\r\n");

  // Read the answer until the module is silent for 500 ms
  unsigned long lastByteTime = millis();
  char lastChar = '\n';
  while (millis() - lastByteTime < 500) {
    while (bt.available()) {
      lastChar = (char)bt.read();
      Serial.write(lastChar);
      lastByteTime = millis();
    }
  }

  // Make sure the next output starts on a new line
  if (lastChar != '\n') {
    Serial.println();
  }
}

void setup() {
  Serial.begin(9600);  // Serial Monitor speed
  bt.begin(9600);      // Factory baud rate of the JDY-18

  delay(500);          // Give the module time to start
  Serial.println("JDY-18 test started");

  // Basic queries, accepted while no phone is connected
  sendCommand("AT+VERSION");  // Firmware version
  sendCommand("AT+NAME");     // Advertised name
  sendCommand("AT+BAUD");     // Baud rate code
  sendCommand("AT+LADDR");    // Bluetooth MAC address

  Serial.println("Bridge ready. Type AT commands or connect from a phone.");
}

void loop() {
  // Module -> Serial Monitor (AT answers or data sent by the phone)
  if (bt.available()) {
    Serial.write(bt.read());
  }

  // Serial Monitor -> module (AT commands or data for the phone)
  if (Serial.available()) {
    bt.write(Serial.read());
  }
}