Hi Peter - I looked at the link to the microphone detection method which is clever. I definitely tried several of the methods mentioned and also a vapor sensor.
My main method for aeroponics mist sensing now is using a liquid flow sensor (Adafruit sells) that measures volume…averages about 275ml per cycle (accuracy is probably +/- 10%). That is recorded in the datalog…when I run down in the nute Tank or if a connection fails the volume drops significantly below that or quadruples, respectively.
My main hassles are pH probe ground loops and measuring nute reservoir tank volume which I will post about in some detail soon.