I tried many ways the only one that worked for me was to plug the arduino sepparately to 5Vpower supply.
Post a diagram. And the code (use code tags).Read the forum rules before you do.A common 'mistake' is connecting the TX/RX of the BT module to pin 0,1 of the Uno.A second on is leaving the two-resistor RX level shifter out.(the HC-05 is a 3.3volt device, but powered from 5volt)Leo..
1. The BT RX is connected to Arduino TX, The BT TX is connected to Arduino RX
2. The BT won't work when connected to 3.3V
3. What do you mean by RX level shifter?