HC-05 It does not respond to the AT command

Using Arduino Project Guidance
1

Hi,

I have an HC-05 Bluetooth module that I connected to an Arduino Uno R3 board.
Pressing and holding the button will enter Command mode, but will not respond.
The module does not respond to AT commands, even though I have tried everything. I have also changed the COM ports and the UART speed, but no response is received.

I have another module, which is not quite the same, but it is HC-05 and it works perfectly.

HC VCC to Ar. 5V
HC GND to Ar. GND
HC TX to Ar. pin 2.
HC RX to Ar. pin 3.

#include <SoftwareSerial.h>
SoftwareSerial HC05(2,3);

void setup() {
	Serial.begin(9600);
	Serial.print("Enter AT commands:");
	HC05.begin(38400);
}

void loop() {
  if (HC05.available())
    Serial.write(HC05.read());
  if (Serial.available())
    HC05.write(Serial.read());
}
2

It’s highly unlikely that SoftwareSerial will,work reliably at 38400.
Good luck, you might get it up on a faster cpu.

3

Tried it at all speeds, but there is no response to AT commands.

4

excluding AT commands, are you able to make the module works in any way?
Are you able to determine if it is a faulty module (as one of yours seems to works flawlessly)

5

The module seems fine, enters AT mode, but does not respond to commands.
Maybe there is an ENTER or end-of-line problem, but I don't know how to solve it.

6

Data rate of HC05 in AT Command Mode is: 38400. For Normal Mode operation, the data rate is: 9600.

7

I regularly get SoftwareSerial to work at 38400, but no faster for sure. This on an Uno with short wires (6") between the Uno and HC05.

The posted code works fine with my Uno with HC05 connected to pins 2 and 3.

I always use a voltage divider on the Uno TX to HC05 RX to drop the 5V to 3.3V. Do you have that voltage divider? Also I do not use the button to put the HC05 into AT mode. On some the button will give you limited AT mode functionality. I connect the EN input to 3.3V before powering the hc05 with 5V to put it into AT mode. That seems to allow all of the AT commands.

Although powered by 5V the HC05 inputs are not 5V tolerant. The RX and EN pins should see no more than 3.3V. You may get away with 5V but maybe not.

Here is a lot of good information on HC05 from Martyn Currey.

Here is how I get my HC05 modules to work in AT mode.

8

I have voltage divider between HC RX and Ar. TX.

9

It worked. Thanks!
Solution: EN to 3.3V

12

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