HC-05 Bluetooth module : Pairing problems


I got some trouble with one of the HC-05 Bluetooth modules.

I am using a Pro Mini 3.3V 8MHz.
For some first testing I put a software serial example sketch onto the Pro Mini.
I connected D10/D11 with the serial I/O pins of the HC-05 and GND to GND and
Vcc to 3.3Vin.
The HC-05 starts blinking in a hurry.

I took my Android tablet and switch on Bluetooth.
The module shows up as "HC-05" and I selected it to pair with it.
A dialog pops up, asking me fot the password "1234".
This was accepted (I checked with a wrong one, which was rejected at once)
and the LEDs of the HC-05 start blinking slowing.
Then it falls back to hastily blinking and my tablet says "Cannot communicate with HC-05".
Pairing wasn't done.
A Bluetooth terminal Android app also states after trying to pair "Bad MAC addr.".

This has worked before...

I have no clue what happened here.

What can I do to revive this Bluetooth module?

Any help is very appreciated - thank you very much in advance!
Best regards,

Not enough volts, perhaps? You don’t describe the HC-05 you are using, but most are on boards using 3.6 > 6v.

I agree with Nick. 3.3v isn't enough when powering through the vcc pin on the breakout board. 3.6v is really the lowest you can give it due to the voltage regulator.

If you really need to use 3.3v you could connect the 3.3v directly to the vcc in on the actual BT module (the small daughter board).