Hello I want to get an arduino get status of bluetooth hc 05 if connect with device or not . I'm trying by myself and search on internet website but I can't find useful things.
Different Bluetooth adapters (using the HC-05 module) provide different signals, besides its Rx and Tx. Most bring out a "key" input that puts the module into command mode where serial communication is between the external pins and the module itself - 'AT' commands & queries to the module's firmware. When the module is not in command mode, the firmware just passes serial data through the Bluetooth radio, ignoring the content. Some provide an LED- or State signal that you can read (or observe on an LED) to know whether the devices is paired (communicating) or unpaired (in command mode).
On some, this is a simple logic signal; on others it is a square wave of 1/2 to 1 Hz which means your code has to track the signal to know whether it is static (typically High when paired) or toggling (for unpaired/waiting to pair).
You need to read your module's datasheet to find out the behavior of this signal on your particular module. If you connect an LED to this signal, or your module has one on the board, you can often make a good enough guess by observing it with a stopwatch. Either way, you then need an Arduino function that samples the LED periodically, remembering what state it saw and for how long, to decide whether the LED is blinking or is steady.