HC-05 won't respond to AT commands

Using Arduino Programming Questions
1

I have tried 4 different types of bluetooth modules and attempted to troubleshoot using all the other posts but nothing seems to work. I can get the module in AT mode (seen by the slower blinking rate) but no matter what I do it wont respond "OK" when I give it the most simple "AT" command. I have followed this guide exactly and get different results. Please help
https://www.gme.cz/data/attachments/dsh.772-148.2.pdf

2

colinjalbert1:
I can get the module in AT mode (seen by the slower blinking rate) but no matter what I do it wont respond "OK" when I give it the most simple "AT" command. I have followed this guide exactly and get different results. Please help
https://www.gme.cz/data/attachments/dsh.772-148.2.pdf

Which process in the guide did you follow, or have you tried all of them?

Have you tried changing the baud rate in the sketch to 9600 and then testing with the button pressed and the button released (or the KEY/EN pin pulled to GND and pulled to 3.3v)?

3

I have tried method 1,2 and 4. I didnt with 3 since it was considered "mini" AT mode. I have tried soldering a wire to pin 34 connected to 3.3v which gives me the slow pulse light displaying AT mode but I never get a response from my serial monitor

4

Have you set the line terminator in the serial monitor to \r\n ?

5

This might be a simple matter of slack wiring. Check Rx>Tx and Tx>Rx. Best guidance is here

6

By connecting EN directly to the 3.3v pin on the arduino and changing the Baud rate to 38400, I was able to succesfully enter AT mode for both arduinos and pair them together (both lights now blink together every two seconds when I turn them on).

The new problem is that when I open the serial monitor for either, I receive a constant line of reverse question marks, I believe this is due to the baud rate or something else interfering with the signal. Does anyone know how to troubleshoot this?

7

There is only one baud rate for working in AT mode with HC-05 - 38400. It was likely the problem all along. If your module has a button,you shouldn't need to use the EN pin. Just hold button when 5v power is applied. Baud rate doesn't interfere with the signal but the rates on the monitor and hardware serial must match.

8

I think this is incorrect, I have both bluetooth module zs-040 connected at 9600 baud rate, and i did in fact need the EN pin to have a voltage to enter an AT mode which responded. It all works now btw