Whilst this thread has not not had a post for 120 days, I thought I would post my experience with the HC05.
I spent many, many hours getting nowhere with the HC05 module. I read many many posts and they did not get me very far very quickly.
The documentation is very vague & contains many errors.
I only had intermittent results if any at all.
My problems were that I was not paying much attention to the carrier board that the HC05 comes on. There seem to be significant variation of these. Some (like mine have a on-board regulator & some do not.
I was also paying to much attention to the warnings NOT TO APPLY 5V to these boards.
Well, applying 3.3 or so to these boards I was able to intermittently get into AT mode, but then the unit would refuse to operate in communication mode.
I tracked it down to the fact that the unit needs to have at least 3.8V connected to the board in order for the regulator to produce enough voltage to drive the HC05 module reliably.
It actually states on the board that the Vcc to the carrier board should be 3.6V-6V, but I reckon it should be 3.8V-6V or so.
In fact unless it is battery operated, connecting Vcc = 5V is the way to go!
Whilst the RX , TX & EN(KEY) are 3.3V , they seem to be +5V compatible as I have not had any failure.
Getting it into AT mode.
No instructions or circuit come with the carrier board. In my case it has a switch, but it was never clear what the switch is there for. However, I traced the circuit & I found that the switch connects between the KEY input & the HC05 and the KEY pin on the carrier board.
To put it into AT mode +3.3V needs to be applied to the KEY pin AND the push button must be pressed, while power is supplied to the unit. Once it is in AT mode
the 3.3V can be removed and the switch released.
A convenient method would be to run a strap between 3.3V on the HC05 module & the KEY pin.
Only pressing the switch is then required at power up.
It is all so bleeding obvious, once you know!
I hope these comments may help someone!