user68554: I have a HC-05 Bluetooth module Version (+VERSION:2.0-20100601).
I am using Linux Mint Rosa on an Acer laptop
Section 1 - How it's wired
Wiring
HC-05       Arduino
VCC         5V
GND         GND
TX          pin 1
RX          GND via voltage divider (GND to 2k resistor{2k to HC-05 RX and a 1k resistor} 1k to pin 0)

Section 2 - Sequence to get into AT command state
The sequence I use to get the BT module in AT command state

Unplug the Arduino Uno
Unplug both the RX and TX
Press the button on the HC-05
Plug in the Arduino
HC-05 LED flashes 1 time every 2 seconds
Initialize com ports via Linux terminal - sudo chmod 0777 /dev/ttyACM*
Upload an empty sketch
Plug in the HC-05 RX to Arduino pin 0, and TX to pin 1
Open the Serial monitor
Set Both NL & CR  and 38400 baud

Section 3 - AT commands issued
I use the following AT commands with the noted results.
AT                                  > OK
AT+ORGL                             > OK
AT+RMAAD                            > OK
AT+VERSION  +VERSION:2.0-20100601   > OK
AT+ADDR     +ADDR:98d3:b1:fd85b0    > OK
AT+NAME=Master1                     > OK
AT+UART  +UART:38400,0,0            > OK
AT+ROLE  +ROLE:0                    > OK  

NOTE:HC-05 is set to slave and it will pair (see Section 4 below)
THE PROBLEM IS AFTER PAIRING, I RETURN TO AT COMMAND MODE (Section 2) and SET ROLE=1 (Section 5) BUT IT WILL NOT PAIR IN MASTER MODE.
Section 4 - Pairing
I do the following to pair the HC-05 to my phone

Unplug the Arduino
Plug the Arduino back in
HC-05 LED flashes quickly blink/blink/blink
Android phone>settings>connections>Bluetooth>Scan
1 device found > Master1 > pair 1234
Android app > Serial BT terminal>device>Master1>connected
Once Android app connects:
HC-05 LED flashes blink/blink 2 seconds then blink/blink
Remove the RX and TX cables from Arduino and put a jumper to connect HC-05 TX to RX (loopback)
Serial BT terminal>hello>send
Output both green and blue - which means the data was sent via RX and returned via TX.

Section 5 - change ROLE=0 (slave) to ROLE=1 (Master)
I then follow the same sequence that I used previously in Section 2 to return to AT command state.
Issue the following AT commands
AT                      > OK
AT+ROLE  +ROLE:0        > OK
AT+ROLE=1               > OK

Since I changed the configuration I unpair the device on my phone.
I then follow the same sequence that I previously used in Section 4 to pair the HC-05 to my phone

HC-05 LED flashes quickly blink/blink/blink
Android phone>settings>connections>Bluetooth>Scan - CAN'T FIND THE DEVICE.

If I return to AT Command mode and change AT+ROLE=0 it will Pair.
In Master mode:

I tried to swap the TX and RX pins - won't pair.
I tried to pair with the TX and RX removed from the Arduino - won't pair.
I tried NOT UNpairing the device on the phone but it won't communicate with it via the android app once I change it to Master (Section 5).
As I mentioned above if I return to AT Command mode and change AT+ROLE=0 it will Pair.

Lastly I have 2 other HC-05 modules and they all fail to pair when set to Master mode, so I'm thinking I'm missing something but can't figure out what it is.
I would appreciate hearing from anyone with the same problem and anyone who can determine what I'm doing incorrectly.

user82452: You might have already solved your problem, but I just wanted to say that a HC-05 Blueooth module will only connect to a phone when it is in slave mode. The phone acts like a master, and therefore, it can't connect to another master.

68554: <p>I have a HC-05 Bluetooth module Version (+VERSION:2.0-20100601).
I am using Linux Mint Rosa on an Acer laptop</p>
<p><strong>Section 1 - How it's wired</strong>
Wiring</p>
<pre><code>HC-05       Arduino
VCC         5V
GND         GND
TX          pin 1
RX          GND via voltage divider (GND to 2k resistor{2k to HC-05 RX and a 1k resistor} 1k to pin 0)
</code></pre>
<p><strong>Section 2 - Sequence to get into AT command state</strong>
The sequence I use to get the BT module in AT command state</p>
<ul>
<li>Unplug the Arduino Uno</li>
<li>Unplug both the RX and TX</li>
<li>Press the button on the HC-05</li>
<li>Plug in the Arduino</li>
<li>HC-05 LED flashes 1 time every 2 seconds</li>
<li>Initialize com ports via Linux terminal - sudo chmod 0777 /dev/ttyACM*</li>
<li>Upload an empty sketch</li>
<li>Plug in the HC-05 RX to Arduino pin 0, and TX to pin 1</li>
<li>Open the Serial monitor</li>
<li>Set Both NL &amp; CR  and 38400 baud</li>
</ul>
<p><strong>Section 3 - AT commands issued</strong>
I use the following AT commands with the noted results.</p>
<pre><code>AT                                  &gt; OK
AT+ORGL                             &gt; OK
AT+RMAAD                            &gt; OK
AT+VERSION  +VERSION:2.0-20100601   &gt; OK
AT+ADDR     +ADDR:98d3:b1:fd85b0    &gt; OK
AT+NAME=Master1                     &gt; OK
AT+UART  +UART:38400,0,0            &gt; OK
AT+ROLE  +ROLE:0                    &gt; OK  
</code></pre>
<p>NOTE:HC-05 is set to slave and it will pair (see Section 4 below)</p>
<p>THE PROBLEM IS AFTER PAIRING, I RETURN TO AT COMMAND MODE (Section 2) and SET ROLE=1 (Section 5) BUT IT WILL NOT PAIR IN MASTER MODE.</p>
<p><strong>Section 4 - Pairing</strong>
I do the following to pair the HC-05 to my phone</p>
<ul>
<li>Unplug the Arduino</li>
<li>Plug the Arduino back in</li>
<li>HC-05 LED flashes quickly blink/blink/blink</li>
<li>Android phone&gt;settings&gt;connections&gt;Bluetooth&gt;Scan</li>
<li>1 device found &gt; Master1 &gt; pair 1234</li>
<li>Android app &gt; Serial BT terminal&gt;device&gt;Master1&gt;connected</li>
<li>Once Android app connects:</li>
<li>HC-05 LED flashes blink/blink 2 seconds then blink/blink</li>
<li>Remove the RX and TX cables from Arduino and put a jumper to connect HC-05 TX to RX (loopback)</li>
<li>Serial BT terminal&gt;hello&gt;send</li>
<li>Output both green and blue - which means the data was sent via RX and returned via TX.</li>
</ul>
<p><strong>Section 5 - change ROLE=0 (slave) to ROLE=1 (Master)</strong>
I then follow the same sequence that I used previously in Section 2 to return to AT command state.</p>
<p>Issue the following AT commands</p>
<pre><code>AT                      &gt; OK
AT+ROLE  +ROLE:0        &gt; OK
AT+ROLE=1               &gt; OK
</code></pre>
<p>Since I changed the configuration I unpair the device on my phone.
I then follow the same sequence that I previously used in Section 4 to pair the HC-05 to my phone</p>
<ul>
<li>HC-05 LED flashes quickly blink/blink/blink</li>
<li>Android phone&gt;settings&gt;connections&gt;Bluetooth&gt;Scan - CAN'T FIND THE DEVICE.</li>
</ul>
<p>If I return to AT Command mode and change AT+ROLE=0 it will Pair.</p>
<p>In Master mode:</p>
<ul>
<li>I tried to swap the TX and RX pins - won't pair.</li>
<li>I tried to pair with the TX and RX removed from the Arduino - won't pair.</li>
<li>I tried NOT UNpairing the device on the phone but it won't communicate with it via the android app once I change it to Master (Section 5).</li>
<li>As I mentioned above if I return to AT Command mode and change AT+ROLE=0 it will Pair.</li>
</ul>
<p>Lastly I have 2 other HC-05 modules and they all fail to pair when set to Master mode, so I'm thinking I'm missing something but can't figure out what it is.</p>
<p>I would appreciate hearing from anyone with the same problem and anyone who can determine what I'm doing incorrectly.</p>
 82452: <p>You might have already solved your problem, but I just wanted to say that a HC-05 Blueooth module will only connect to a phone when it is in slave mode. The phone acts like a master, and therefore, it can't connect to another master.</p>
