I am currently working on a project that requires communication between an android phone(galaxy s4) and an ATmega328 microprocessor. To connect these devices wirelessly I'm using an HC05 bluetooth module and to understand the connection I'm using pre-built arduino codes(turn LEDs on and off) and an android app called blueterm.

This connection is established and able to transmit data when connected to the Arduino uno, but as soon as this chip is removed and connected to a standalone breadboard the connection fails. The standalone breadboard works fine and has been tested with many other projects and I have attached the breadboard connection below. The HC05 when connected to the breadboard changes the blinking pattern to notify the user it is connected but the serial connection is never made. Any help would be greatly appreciated, if any other information is needed feel free to ask.

enter image description here

  • It looks like the HC05 should be moved one row to the left.
    – Gerben
    Commented Jun 21, 2014 at 12:55
  • It might be a bad angle but the last pin is not needed on the HC05 unless editing its internal settings. The connection is not changed when moving back to the arduino just the pins that go to the atmega328 are moved from the breadoard to the arduino. Commented Jun 23, 2014 at 15:29
  • I guess your module has a different pinout that the one I found online. I also check, but the Uno doesn't have any pull-up resistors, so that's not it. Does your atmega run off 3.3V too?
    – Gerben
    Commented Jun 23, 2014 at 19:50
  • Are you sure pin TX (on the Bluetooth side) is connected to pin 0 on the chip, and RX is connected to pin 1? Commented Jun 24, 2014 at 0:48
  • I would like to give some suggestions: If BT module connects to a phone (LED is solid, no blinks) and no data received, i would do some tests like: connect Rx-Tx and check does MCU echo typed letter. Connect Rx-Tx of BT module and check on android does it echo typed message.
    – Martynas
    Commented Nov 27, 2014 at 8:21

2 Answers 2


If the LED is blinking, the device is waiting to pair with another Bluetooth transceiver (your phone). Once paired, the LED will stay lit. The factory-set pairing code is usually 1234. I can't tell from the photograph how the HC-05 Rx & Tx are wired to your ATmega328, but note that it must be cross-connected; that is Rx -> Tx and Tx -> Rx.


I had same issue and solved by below mentioned layout.HC05 with Atmega328

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