Place a note block
Place a tripwire hook on one side of the note block
Place a second tripwire hook directly opposite the first one
Connect the two hooks with tripwire string
Attach a fishing rod to the tripwire setup by using it to trigger the hook area
Run redstone dust from the tripwire hook output to the device you want to activate
Test the setup by casting the fishing rod at the tripwire line
Adjust the hook and string placement if the signal does not trigger correctly