HC-05 BT module is unable to connect with moble device

I'm working on simple led the On-Off controlling project. For that i bought HC-05 BT Module.
Pin Description : Tx,Rx,vcc=5v,gnd are perfect. when I apply power supply Red led light is blinking in some frequency. I can pair perfectly. But when I connect my device to HC05 its showing "Unable to connect device check your device is on "

You don't say anything about your "mobile device", but it sounds rather like an iPhone.

No @Nick_Pyner , My device is android, and there is no problem with device. HC05 is not connecting but its pairing perfectly

HC05 is not connecting

Not connecting to what? A bluetooth terminal app? An app you wrote? An app found on the internet?

sanukyadav:
HC05 is not connecting but its pairing perfectly

The HC-05 doesn't do the connecting - or the pairing, for that matter.
Android does the pairing in Settings.
Android does the connecting in the app.

If you wrote the app yourself, use an app from Playstore - just a standard plain-vanilla terminal.

  1. Check that you have connected the HC05 Module with UNO as per following diagram. The voltage divider circuit is needed as the RX-pin of HC05 is not 5V tolerant.

  2. Is the Red-LED of the BT Module continuously blinking?

  3. Have you installed a Bluetooth Terminal (BTT) in your android based smart phone?

  4. Check that the smart phone has detected your BT Module. If SN is asked, enter 0000 or 1234; they usually work.

  5. Connect your BTT with the BT module. Check that the RED-LED is now blinking once a while.

  6. Upload the following sketch in the flash of your UNO.

#include <SoftwareSerial.h>
SoftwareSerial BTserial(2, 3); // SRX | STX
// Connect the HC-05 TX to Arduino pin 2(as SRX).
// Connect the HC-05 RX to Arduino pin 3 (as STX) through a voltage divider.

void setup()
{
 Serial.begin(9600);
 BTserial.begin(9600);
}

void loop()
{
 if (BTserial.available())
 {
   byte x = BTserial.read();
   Serial.write(x);
 }

 if (Serial.available())
 {
   byte y = Serial.read();
   BTserial.write(y);
 }
}
  1. Check the functionality of the communication link:
    BTT <----> BT <----> UNO <----> Serial Monitor

Thank you all for your valuable replies. Here i will give more clarity about my problem_

1- I didn't use voltage divider ckt. (Will it results in this kind of error ?).

2- I have used my own app which is created by using app inventor MIT, I referred this link-

3- Red LED is blinking in some frequency when I scanned using a smartphone, I got the device ID listed in available BT, and I'm able to pair using 1234 pwd.

I will follow these instruction MR. @GolamMostafa , @cattledog, and @Nick_Pyner soon..

s

I have used my own app which is created by using app inventor MIT, I referred this link-
http://www.instructables.com/id/Build-Android-Bluetooth-App-for-Arduino/

I dowloaded tha .aia file referred to in the first response to the tutorial. The forum won't allow me to attach the .aia file.

I could get that .aia file with app inventor and the ai2 companion on my phone to connect with my HC05.

The Arudino program does not appear to be correct.

EDIT: The aia file I used is linked in one of the later responses to the tutorial, not the first one. There are several versions of Arduino code on the tutorial, maybe one of them works. All in all, not a great "Instructables".

sanukyadav:
1- I didn’t use voltage divider ckt. (Will it results in this kind of error ?).

No. If you check Google Images, you will see the divider is used in only about half of them. It IS good practice.

2- I have used my own app which is created by using app inventor MIT,

A really bad idea, but apparently you got lucky. Special kudos to Cattledog is in order.

3- Red LED is blinking in some frequency when I scanned using a smartphone, I got the device ID listed in available BT, and I’m able to pair using 1234 pwd.

OK. This means Android <> Bluetooth is kosher. It does not mean Buetooth<>Arduino is kosher.
Check your Arduino/wiring Rx>Tx and Tx>Rx.

You might find the following background notes useful.

http://homepages.ihug.com.au/~npyner/Arduino/GUIDE_2BT.pdf
http://homepages.ihug.com.au/~npyner/Arduino/BT_2_WAY.ino

Could you do something? I have the same problem. Can write the AT comands but cant connnect with my phone

but cant connnect with my phone

What model/type of phone? Is the phone paired with the HC05? What program are you running on the phone which is failing to connect?

Have you read the recommended background notes

You might find the following background notes useful.
http://homepages.ihug.com.au/~npyner/Arduino/GUIDE_2BT.pdf
http://homepages.ihug.com.au/~npyner/Arduino/BT_2_WAY.ino

Your problem is not the same. IF you really can write the AT commands, it means the Arduino<>Bluetooth is kosher, but it does not mean the Android<>Bluetooth connection is kosher. All problems in that arena are at the phone end.

Nick_Pyner:
The HC-05 doesn't do the connecting - or the pairing, for that matter.
Android does the pairing in Settings.
Android does the connecting in the app.

If you wrote the app yourself, use an app from Playstore - just a standard plain-vanilla terminal.

That was very helpful

[quote=‚Äúnandeeshahk, post:14, topic:528810‚ÄĚ]
newer versions of hc-05 Mlt V4.4 Bt
[/quote] The HC-05 is a ‚Äúclassic‚ÄĚ Bluetooth 2 device, and it is pretty clear that that is what the OP was using. The BT05 is a Bluetooth 4 (BLE) device, and not a newer version of the former, although it may fit on the same breakout board. It is also not particularly well-suited as a replacement. This may, or may not be explained in that clunky video. If not, as is likely, check the Martyn Currey website, where there is a good overview of these devices‚Ķ

1 Like

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.