Bluetooth HC-05 keep blinking

Hello everyone.

I have purchased one bluetooth HC-05 (master/slave). I followed the instruction and code at Configuring your Bluetooth Module for the Communication between Scratch and Arduino but the red LED in HC-05 still kept blinking. HC-05 also didn’t response my AT command.

Maybe I did something wrong ? Can anyone help me ?




quocbao9996: Maybe I did something wrong ?

Probably, but maybe easily fixed.

Here is a guy who knows what he is doing - contrary to that other mob.

Note that here have been recent changes to these cheapo boards. Try the line

pinMode(2, INPUT_PULLUP);

in the setup if you are not getting a result. Pin2 is Rx. Needless to say, if you run on proper hardware serial, it would be Pin0.

What blink/flash pattern are you getting? If it is about 5 quick blinks per second then you are in communication mode. To enter AT mode using 38400 press and hold the little button switch while powering on the HC-05.

The link posted above gives full details.

The board is not 5V tolerant and you shouldn't be connecting the BT RX pin directly to the Arduino. This will slowly damage the Bluetooth module. The BT RX pin is 3.3v and the Arduino is 5V. An easy way to covert the voltage is a voltage divider made from resistors between the Arduino and the BT RX pin.

The TX pin can be directly connected to the Arduino. The Arduino reads 3.3V as HIGH.

Sorry for slow replying because of my busy work :smiley:

After I followed the instruction that Nick_Pyner gave to me, this is what I receviced …


I guess my HC-05 was burned before.

I'm afraid the picture merely means that everything is OK with Arduino and monitor. This is not actually relevant to getting AT mode. The LED on bluetooth confirms that. It should flash at two second intervals. Do you see that?

It might be worth while taking a step back.

Connect the BT module to GND and VCC, don't worry about connecting to the Arduino. The LED should be blinking about 5 times a second.

Now remove the power, press and hold the little push button switch, reconnect the power (keeping the button switch closed). After seeing the LED come on you can release the button switch but don't release the switch too soon.

The LED should now flash on/off every 2 seconds or so; on for 2 seconds, off for 2 seconds. This means the module is in AT mode at 38400.

If you are still having issues post a clear photo of the board; front and back.

The garbage characters in the serial monitor can mean you have the wrong baud rate. I get similar results when I use software serial at 9600 and the board is set for 38400.

Have you have the module talking to another device such as an Android device?

hello everyone, I just follow the step such as power off the module-hold the small button-connect back supply-release small button. After I have done for this step. The LED blink every 2 second. Then I go to serial monitor. First I have write "AT" it display error (0). Second I write "AT" it display OK. next when I write"AT+NAME?" nothing display on serial.

Could anyone help me for this case?