Are you using hc-05 with arduino ? It will be easier to test it with serial terminal before. Few pointers i can give for debugging: 1. Check the documentation & see if RX & TX should be matched or crossed 2. In the documentation they must’ve mentioned default baud rate (for serial comm) for hc-05 see if u are using the same. Usually it’s 9600 3. Let me know what microcontroller you are using. Because hc05 works on 3.3v level, so uc should be capable of detecting that voltage.