Arduino HC-05 Bluetooth Module Usage and AT Commands

Normally, you can connect the HC-05 module to Arduino as shown above, but if you take my suggestion, I recommend connecting the TXD and RXD pins to any two digital pins on the Arduino and using a library on Arduino to convert them to RX and TX.

To make AT commands work, you need to connect the EN pin to 5V, otherwise, it will not allow you to change the HC-05 module’s name or baud values.

Sending AT Commands to the HC-05 Module via Arduino

When you upload the code below to your Arduino board, you can send AT commands to the HC-05 module over the serial connection.

#include <SoftwareSerial.h>
SoftwareSerial mySerial(10,11); // RX, TX
void setup() {
 Serial.begin(9600); // PC and Arduino connection
 pinMode(9,OUTPUT);  // EN connection
 digitalWrite(9,HIGH); // EN active
 Serial.println("Enter AT commands:");
 mySerial.begin(38400); // HC-05 connection
}

void loop(){
 if (mySerial.available())
 Serial.write(mySerial.read()); // message to HC-05
 if (Serial.available())
 mySerial.write(Serial.read()); // response from HC-05
}

When uploading code to the board, disconnect the HC-05 Module from the Arduino; otherwise, you may get errors. After the software is loaded to the board, reconnect it.

Don’t forget to select the option with NL and CL on the serial screen; otherwise, responses will not come.

To put the HC-05 module into AT mode, hold down the small button on the module and power it up, i.e., you need to hold down the small button while the module is off.

If the light on the module blinks every 2 seconds, it means it has entered AT mode.

Click here for the documentation document.