HC-05 won't start correctly each time - need to reset

Hi everybody,

I'm using an HC05 module (only the HC-05 module, not HC-05 + breakout board). I put 3.3V on VCC, GND, RX and TX to Arduino's TX and RX pins. Key's pin is pulled low via 4.7K.

When I power up the board: sometime the module starting (led is blinking and I can connect with my android) sometime it does'nt start: led is OFF and I can't connect with my android. In this case if I put the reset pin low and then release, the module is starting !

Do you know why I have this problem :o ? What can I do for the module start all the time automatically?

Thanks a lot...

You can start by ensuring the power and the wiring is kosher all the time. You might also reconsider why you chose a bare HC05 in the first place, as you might find that the Arduino 3.3v supply is inadequate.

Hi,

I did not understand "the power and the wiring is kosher all the time", can you explain me please ? (sorry for my english... :confused: ) The wiring can not move as I have made a little PCB for the HC-05 + power supply.

The power of the module is not from the Arduino's power supply. It came from : 12V battery -> pololu 3.3V step down + decoupling capacitor + bypass capacitor.

Hello, put 5V through the VCC, only the VCC can handle the strength of 5V however it can handle it, however if you accidently put 5v into any other pin you risk harming your module to be careful.

OK, even though you have gone to the trouble of making a PCB, I would still suspect power and connections. Your bare module is 3.3v device, and only an idiot would lean 5v against the VCC in the hope of solving the problem.

Nick_Pyner: OK, even though you have gone to the trouble of making a PCB, I would still suspect power and connections. Your bare module is 3.3v device, and only an idiot would lean 5v against the VCC in the hope of solving the problem.

ok first off I'm not an idiot, and I only put 5V through the VCC and mine works perfectly fine, also almost every module can handle 5V on VCC but ONLY VCC. I did not say put 5V on every pin, as that would fry his board

Nick_Pyner: OK, even though you have gone to the trouble of making a PCB, I would still suspect power and connections.

If I do a reset on the bluetooth module after power up the PCB, all is ok, the Bluetooth work fine ! --> So if I have a problem of power and connections, the module normally don"t work at all, no ? (I try to find the source of the problem, but d'ont find them :confused: )

Hexor: So if I have a problem of power and connections, the module normally don"t work at all, no ?

That sounds reasonable but, in the absence of any better conclusion, the power is still suspect. It might just be marginal. There is a reset pin on the bare module but I don't see why you are using it - or ever need to. You had better come good with.

  1. your intentions
  2. the code
  3. a clear wiring layout

as you should not be having problems like this.