Bluetooth module entered AT mode but serial monitor not responding

My HC-05 bluetooth module has entered AT mode and it is blinking every 2 seconds, but the serial monitor is not responding. I've read all the posts on the forum but none of them seem to be working. This is urgent as i have a competition coming up. I've connected the HC-05 via breadboard.

what do you have set as your BAUD rate ? are you reading from within a sketch, if so where is it. (please post using </> code tags.) how have you wired it up ? Standard questions that will help in identifying the problem.

Urania123:
My HC-05 bluetooth module has entered AT mode

Have you succeeded using Bluetooth in communications mode?

Deva_Rishi:
what do you have set as your BAUD rate ? are you reading from within a sketch, if so where is it. (please post using </> code tags.) how have you wired it up ? Standard questions that will help in identifying the problem.

I've set the BAUD rate as 38400. The instructions I have read so far tell me to upload a blank sketch and then open the serial monitor. I'm doing this but when I enter AT into the serial monitors address bar nothing happens.

I've wired it in the following way-
HC-05 VCC to Uno 5v
HC-05 GND to Uno GND
HC-05 TX to Uno RX (Tutorial requested to switch the pins before uploading)
HC-05 RX to Uno TX

Thanks in advance for any help! :smiley:

Urania123:
HC-05 TX to Uno RX (Tutorial requested to switch the pins before uploading)
HC-05 RX to Uno TX

what are the TX-RX pin nrs (on my uno the writing refers to the tx-rx of the USB in that case you'd have connected correctly, maybe do a swap over just to make sure that is not the issue. Please provide link to the exact model BT-unit and tutorial referred to.

This is the tutorial I used

BTW I'm a newbie to Arduino, so please keep it simple :slight_smile:

Your intentions are far from clear. The tutorial you allude to does not appear to to have anything to do with your original post. This suggests that you have entered AT mode by mistake. So, did you intend to enter AT mode and, if so, why?

IF your intention is to flash LEDs, you are not likely to need to enter AT mode but the code in the tutorial will probably not work as it is. It might if you change the baud rate in the code to 9600. This is because the default baud rate is usually, if not always 9600.

IF your intention is to configure the HC-05 in AT mode. The tutorial is useless.

I did intend to enter AT mode, the tutorial was supposed to show me how to set it up in the beginning. I tried all the BAUD rates including 9600. 38400 was the initial default value. My main intention is to configure one of my modules as master and the other as slave. I entered AT mode to test out the module.

Thanks in advance for any help :slight_smile:

OK, you first need to be aware that there are two separate modes of operation for HC-05 and they cannot be in both at the same time, and the code is slightly different.

AT mode for configuration, and the baud rate required is 38400 - no exceptions, and irrespective of what the communications mode might be. You clearly know what to do in order to get into this mode, and the LED confirms it.

Communications mode for communication, and the baud rate is 9600 by default, but may be changed by re-configuring in AT mode.

I suggest you learn to walk before you try to run, hence reply#2. You might find the following background notes useful, but I think you already know most of it. Note the voltage divider in Bluetooth Tx line.

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

If, by "switching pins" the tutorial suggests switching RxTx, I think it's nonsense. If it really meant, disconnecting bluetooth on hardware serial before uploading, that is fine.

This is an Arduino forum, stick with the Uno to configure bluetooth. A good tutorial on HC-05<>HC-0x is here.. Note that Martyn uses software serial as the bluetooth connection for AT mode, which is conventional.

Nick_Pyner:
Have you succeeded using Bluetooth in communications mode?

Nick_Pyner:
Have you succeeded using Bluetooth in communications mode?

I cannot find a way to enter communications mode. I'm following the tutorials you had mentioned in reply#8. But that doesn't solve my problem. My main aim is to configure my module as master and the other as slave and make them communicate. My module's LED is blinking once every 2 seconds, indicating that its in AT mode but the serial monitor does not respond. I've connected the same way that the MartynCurry tutorial mentions (link below), but nothing seems to be happening. It gave some hope at least.

Thank You!!!

I am stuck again the module will not respond pls help i neeed code

Urania123:
I cannot find a way to enter communications mode.

Communications mode is the power-on default mode. You get into it by using four wires only and keeping your finger off any little button when you turn the power on.

indicating that its in AT mode but the serial monitor does not respond.

This is loose language. If you are not getting any response to your AT commands, it is Bluetooth that is not responding, and probably because you aren't sending any, you just think you are.

Being in AT mode is no guarantee of correct wiring, so check Rx<>Tx,

You already have all the code you need, and several versions of it.

Thank you so much for all the help. The tutorial you suggested was extremely helpful, in fact I referred to several tutorials on the same website. But one problem still remains. I've entered communications mode on the blue tooth module and they're connected but when I enter, lets say HELLO, in the serial monitor,I get random values on the other serial monitor. Please advise.

Thanks so much!!! :slight_smile:

You are out of my league. Try here

Urania123:
but when I enter, lets say HELLO, in the serial monitor,I get random values on the other serial monitor.

if it looks like random values, there is a good chance that the BAUD rate is not correct (for the receiving device) or can you specify random ?

Deva is right. There are four baud rate pairs that must match.

PC1 <> Arduino! <> BT1 2.4GHz BT2 <> Arduino2 <> PC2
........baud.....................baud......................................baud.........................baud
You might as well make them all 9600 for the moment.

Deva_Rishi:
if it looks like random values, there is a good chance that the BAUD rate is not correct (for the receiving device) or can you specify random ?

The BAUD rate (9600) is correct for both. Random values as in a weird y with dots on top of each line. If you know anything about what's happening, please tell me.

:slight_smile: :slight_smile:

Urania123:
The BAUD rate (9600) is correct for both.

"both" does not describe eight settings.

Urania123:
The BAUD rate (9600) is correct for both. Random values as in a weird y with dots on top of each line. If you know anything about what's happening, please tell me.

Exactly... that usually means that the BAUD rate is wrong (somewhere) these y with " .