I have two circuits one having a ultra sound sensor and one other having a relay module. So i'm trying to establish communication between the two to send and recieve data. I just want to know which way is the best so that one arduino will send data only when the other is powered and able to recieve data. So that there is no problem when one circuit is powered on and the other is not and the data is not sent until the connection between the two is established .This is because the circuits are powered by different power sources and the current is not predictable and i dont want any miscommunication happening between them.
any way is okay like rf or wifi or some other methods? Using other devices is also an option like ESP32 which has builtin wifi and bluetooth, But wired is not possible because the distance is too big like about 15-17 meters and using the same power source is not viable for the same reason. Tell me also if the distance im worried about is not a problem?