I’ve been asked to cover this topic multiple times. So, welcome to part one: how to connect HC-SR04 sonar rangefinder to INAV and any flight controller? The answer is simple: don’t. HC-SR04 sonar is absolutely not suited to work on a drone! It picks noise instead of ground echo and above a certain altitude (low altitude by the way) reports rubbish! From time to time it kind of work over concrete but immediately loose measurement capabilities over grass.