GPS Racer: worklog #8 - sonar test platform

I honestly admit, that my 6" quad (codename GPS Racer) was never very pretty. It was just ugly with that GPS tower on the front. Today it got even uglier: I've equipped it with HC-SR04 sonar connected via I2C bus (ATtiny85 to the rescue).

Why, you might ask, have I done something so useless? Answer is simple: to make it less useless. There are at least few problems with sonar and modern flight controllers. First of all, most new boards does not have connections for it. Second of all, it does not work reliably.

It just don't. It was no unreliable that INAV, for example, disabled it for some time completely. Right now it is back, but used only during landing on multirotors. No terrain following or anything like that.

Ultrasound rangefinders like HC-SR04 are very sensitive for any kinds of vibrations. One millisecond it can give valid AGL altitude, second millisecond it can report of-out-range case or completely invalid altitude. Try to archive a solid altitude hold with data like that...

I've decided to try to change that, so I needed a test platform to test some of the ideas for INAV. So, with a little help of ATtiny85 I've created an interface between HC-SR04 rangefinder and any flight controller equipped with I2C interface. Cheap and simple. Does it work? Yes, on a bench. Did not flight tested it yet. If it will work in a real life, expect more posts on that topic. Including some electronic diagrams and ATtiny code. If now, then well, we can just forget it ever happened....