Problem with bluetooth HC-05

i use arduino uno for my cnc project. I want to control my router via bluetooth module HC-05 with grbl cotroller+ app, but i cant get response from hc-05 module in AT mode. All i get is some kind of unreadable symbols and no response on any command. With grbl controller+ app i can connect to module but all functions are inactive. Maybe somebody can help me to solve this problem.


The general convention if pins are labelled conventionally is to connect Rx on one device to Rx on the other and vice versa

However, on a Uno the pins on it marked Rx and Tx are used for the interface to the Serial monitor and as such it is unwise to use them for anything else unless you know what you are doing

The baud rate for the HC05 in AT mode is 38400. There are 2 AT modes. See this page.
I hold the push button switch closed with a mini alligator clip to keep the HC05 in "full" AT mode to change he baud rate and other settings.

Your connection is right if you are using the Uno as a USB to serial converter, but the328 chip needs to be removed or disabled by holding its reset pin LOW. For regular communication it must be RX to TX and TX to RX.

To communicate with grbl the regular baud rate (not AT mode) needs to be 115200.

I have a 2D plotter that has an Uno running grbl and is controlled via Bluetooth with an HC05 so I can help you to get yours to work, but I need to know all about your setup

I tried everything but no luck. I cant get any response in AT mode. Realy dont know where could be the problem. In attachment you can se what massage i get in serial monitor. Also i uploaded grbl which i am using and made photo how everything looks like now. Any ideas?


Which program/app do you use ti control your 2D plotter?

I will describe my setup so you can better know what I need to know to help.

I have a Win 10 PC connected to a HC05 set to master mode through a USB to serial adapter that sends the gcode to another HC05 (in slave mode) that is connected to an Uno running the grbl firmware. Both of the HC05 modules are set to 115200 baud. The PC is running the bCNC gcode sender app,

Before connecting the HC05 modules in their permanent positions, they were attached to a USB to serial adapter and their setups were modified so that they would automatically pair and connect to each other, their baud rates were set to 115200 and their names were changed. The Arduino IDE serial monitor was used as a terminal to talk to the modules while I set them up. I used this howtomechatronics page instructions to set up the modules. The HC05 that is connected to the Uno connects the HC05 TX to the Uno RX (pin 0) and the HC05 RX to the Uno TX (pin 1) through a voltage divider (see the howtomechatronics page).

This Martyn Currey page explains how to use AT mode.

I found this HC05 configurator app helpful.

Please post your photos here so that we don't have to go and download them.

Thank you for your help. I moved forward but not enough. Now i can connect and communicate with HC-05 module. As i mention earlier i am using Grbl controller+ app on my android phone (which is working only with grbl 1.1 or higher version) and i want to control my plasma table. I uploaded grbl 1.1v to my arduino controller but every time i connecting i get message that i am using GRBL 0.9 version. How it can be possible? I uploaded grbl many times from different sources but still getting same massage. Any ideas?

I solved my problems. I watched many videos on youtube how to upload/update arduino grbl from 0.9 to 1.1 version. I used diffrent arduino boards but still didnt get result that i was expecting until i uploaded .hex file to my arduino UNO. And finally it is working. Thank you for your help.

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