About Mission planner, Arduino to Pixhawk

Hi all I have some question about my project. I have old DIY drone using Arduino Due 32 bit from my senior my aim for this project is about avoidance system for quad copter by using ultrasonic sensor. Now I have Arduino Due and Pixhawk I want to connect between Arduino and Pixhawk which Arduino is master and Pixhawk slave how can I do that? What about ground station can I use Mission planner connect to the Arduino? before I come to ask I try to connect Arduino and Misstion planner but it fail, it show that “no heartbeat packets received” how can I fix that?