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Topic: HC-05 Initilised State (Read 411 times) previous topic - next topic


Hi! I'm working on a project involving Bluetooth communication between a raspberry pi 3B+ and two HC-05 modules, each connected to separate Arduino Uno boards. The goal is to transmit sensor data from the two Arduino boards to the RPi, for processing, using Bluetooth. One of the HC-05 module works perfectly fine. I'm able to receive data on the RPi. This module is in the INITIALISED STATE (I found this out through AT commands) and the LED blinks rapidly (around 5Hz) when powered ON. This runs the firmware V2.0-20100601. Baud rate = 9,600 (I used AT+UART?).

The other HC-05 module is able to establish connection with the RPi but, I couldn't receive any data. The received data buffer is empty. I found out that this module is in the PAIRABLE STATE and the LED blinks less rapidly (around 2Hz) when powered ON. I tried to initialise the module using the AT+INIT command but, I got an error 17 message. The firmware is V2.0-20161226. Baud rate=38,400 (again, AT+UART?). I have a question here, what is this baud rate? Is it the rate at which the module sends BT data or is this the AT mode baud rate? I read that the baud rate in the AT mode is 38,400 by default.

What do you think is the issue? Why am I not able to receive data on RPi? And is there a way to bring the module to the INITIALISED mode? Help me out, fellas. This is for a project in my clg and the deadline is around the corner now. Thanks in advance.


What do you think is the issue?
It quite likely to be the result of too much fartarsing about. Since you have been doing that and know how to send AT commands, I believe AT+RESET is the best command to now send to both HC-05s, thereby putting them into slave mode, and in an unknown state that you don't need to know.

You have proven that your HC-05s are compatible with the bluetooth on the raspberry pi. All of your programming is at the Raspberry Pi end, which strongly suggests that you are on the wrong forum.


Thanks for your response. Nope, reset doesn't make any difference.

I did try posting this question on the raspberry Pi forums. Didn't find anything wrong on the RPi side. That's why I thought of posting it here.


Jan 21, 2019, 04:26 pm Last Edit: Jan 21, 2019, 04:28 pm by Nick_Pyner
It is not a case of finding anything wrong on RPi, it is a case of knowing what to do, which you clearly don't - possibly because you are asking the wrong questions over there, or making bad assumptions. The bluetooth on RPi needs to be programmed to communicate with two slaves - hence my comment.  You also may need to have the power supply to Bluetooth under software control. I was wrong about all the programming at the RPi end. You will most probably need to change the name of one HC-05, and you will also probably need to retrieve the address of both, but that is all.

You may find it preferable to ditch the HC-05s for a pair of BLE modules of some sort. It may make things easier at the RPi end.

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