HC-05 Bluetooth module does not respond: baud rate, AT mode and wiring

Most failures are crossed wires or the wrong baud rate. TX of the module goes to RX of the board and the reverse, and the speed must match.

What the message means

The HC-05 talks over a serial link. In normal mode it usually runs at 9600 baud. In AT command mode it uses 38400 baud. If the baud rates or wires do not match, you see nothing or garbage.

Fix it in this order

1. Cross the wires: module TX to board RX, module RX to board TX. Join the grounds.
2. The module RX pin is a 3.3 V input. Use a resistor divider from a 5 V board TX pin.
3. Open the serial link at 9600 baud for data. For AT commands, hold the button while powering the module and use 38400 baud with line endings Both NL and CR.
4. Do not use the Uno pins 0 and 1 while uploading. Use SoftwareSerial pins or a spare hardware serial port.
5. Check the slow blinking LED means AT mode and the fast blinking means waiting to pair.
6. Pair the phone first, then connect with the terminal app.

Why it happens

The HC-05 answers AT commands only in AT mode. Entering it usually means holding the small button while powering the module, after which the LED blinks slowly, about every two seconds. In AT mode the module commonly runs at 38400 baud and expects commands that end with carriage return and line feed.

Set the Serial Monitor to both NL & CR, use 38400 baud, and cross the wires: module TX to the board RX, module RX to the board TX. The HC-05 RX pin expects 3.3 V, so use a divider from a 5 V board. Behaviour differs between clones.

If you see this, do this

Related

Bluetooth robot car, Serial Monitor garbage.

Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.