Tutorial: Programming the HC-05 - AT mode - with Arduino

Tutorial: Programming the HC-05 AT commands - done easily with Arduino

What This Tutorial Covers

In this tutorial I will show you how to wire the HC-05 to Arduino UNO and get into the AT mode all done with CODE. This way there is no need for pulling pins high and low by hand and it is quick and convenient and easy. Also, I will go through the process of changing the bound rate, the name and demonstrate a few other useful AT commands. 

*Please note that this tutorial is for the HC-05.

What You Need

 For this tutorial you will need a few things, here is the list:

- Arduino UNO, but any equivalent should do just fine

- HC-05 with a breakout board, unless you know what your doing. 

- a breadboard and some wires

Set Up

Here are some pictures of the Set Up. Included is also a diagram of the connections made with Fritzing. (Thanks Fritzing!)

A quick run through the connections verbally as they are very simple and easy.

- Arduino pin A1 is connected to the TX pin of the BT.

- Arduino pin A0 is connected to the RX pin of the BT

- Arduino pin GND is connected to GND pin of the BT.

- *** Arduino pin 7 is connected to 5V pin of the BT. ***

- Arduino pin 8 is connected to the KEY pin of the BT. 

Simple, no? A few wires and we are set to upload the code! 

Now, before I slap the code here I want to take the time to explain why we are connecting the 5V of the Bluetooth to pin 7 of the Arduino. This is very simple, in order to get into the AT mode we have to follow a few simple steps and connecting the 5V pin to a variable pin of the Arduino allows us to bring it High and Low as we please. In order to get into the AT mode we have to first pull the 5V and the KEY pins to Low. This is important and often skipped by all the other tutorials and thus it introduces problems for the people trying to follow in the long run. Once they are Low we have to pull the KEY pin High, after a small delay and only then, we pull the 5V pin to HIGH. This results in the BT going into the AT mode and this can be confirmed by sending a serial command "AT" via serial and/or by looking at the HC-05 indication LED; it should be blinking at one second intervals.

The Code

Now finally for the code. I commented it thoroughly and thus I will not explain much of it here in text. I want people to find it easy to program the HC-05 this I'm posting the code as a whole. 

Simply copy this code and upload it to the Arduino. 

/*
This code is in the public domain.
written by Damian Glinojecki
*/

#include 

#define bt_power 7
#define bt_key_power 8
#define indication_led 13

SoftwareSerial BT(A0, A1); // RX | TX

void setup()
{
  // set the pins to OUTPUT
  pinMode(bt_power, OUTPUT);  
  pinMode(bt_key_power, OUTPUT);
  pinMode(indication_led, OUTPUT);
  
  // set the pins to LOW
  digitalWrite(bt_power, LOW);
  digitalWrite(bt_key_power, LOW);
  digitalWrite(indication_led, LOW);
  
  /************************************************
  Setting the pins to low is important because 
  in order for us to get into AT mode the key pin
  has to be set to Ground FIRST. Many tutorials out
  there fail to mention this important fact and 
  therefore many people have problems with getting 
  into the AT mode of the HC-05
  ************************************************/
  
  // make sure the key has been LOW for a bit
  delay(100);
  
  // set the key pin to High
  digitalWrite(bt_key_power, HIGH);
  
  // small delay
  delay(100);
  
  // now power on the BT
  digitalWrite(bt_power, HIGH);
  
  // start our serial so we can send and recieve
  // information from the BT module
  Serial.begin(9600);
  // initiate the BT serial at 38400 which is the default 
  // speed at which the BT AT mode operates at
  BT.begin(38400);
  
  // self explanatory
  Serial.write("For a list of commands, visit: \n");
  Serial.write("Type AT commands  \n\n");
  
  // process complete turn on led 13
  digitalWrite(indication_led, HIGH);
  
  // Send an "AT" command to the AT (without quotes)
  // if response is OK, then we are connected
  // and ready to program the BT module
 }

void loop()
{

  // listen for a response from the HC-05 and write it to the serial monitor
  if (BT.available())
    Serial.write(BT.read());

  // listen for user input and send it to the HC-05
  if (Serial.available())
    BT.write(Serial.read());
    
}

Now to the Programming of the HC-05

In your Arduino sketch you have a very useful tool called the Serial Monitor. Click Tools -> Serial Monitor.

Before we do anything, lets make sure our Serial Monitor settings are correctly set. This is IMPORTANT! 

First off make sure that the boxes outlined in red match yours. 

***Please note that I am using version 1.0.1 of the Arduino software but it should be the same for all of them. 

It is important that your bound rate is set at 9600 or else we wont be able to talk the same "language" as the Arduino is set to understand. Also, make sure that the line editing is set to "Both NL & CR". This is another important detail that many tutorials miss. (I was ripping out my hair not understanding why I cant communicate with the HC-05)

Now for a test type "AT" without the quotes and press enter. You should get a response "OK" as follows:

This is GOOD! This means that we are in AT mode and we are talking with the HC-05 and it hears us! Now we can change some of the settings. You can find the complete list of commands on the bottom of this page.

For starters I will change the name of the Bluetooth. To do this all I need to do is type in the following command: "AT+NAME=QMBTv1" (again, without the quotes) You can substitute "QMBTv1" for anything you like. This is the name I am giving my BT though. Now to confirm that the name was changes lets send another command "AT+NAME?" The HC-05 should respond with the name that we just assigned.

Side Note: Some of you might wonder what does the QMBTv1 stand for. As I mentioned in an earlier post, I want to build a quadcopter. This BT module is going to be the main means of communication with the quad. :) 

Now lets change the bound rate to 115200,1,0. This is just as simple. Send this command "AT+UART=115200,1,0" and then "AT+UART?" to confirm that it was changed successfully. 

If you followed all the steps and got the name and the bound rate to change, then you have done everything right. Congratulations you changed the HC-05 settings! 

Commands for the HC-05

You can find all of them here. Courtesy of linotux, Thanks for listing them! 

CLICK HERE