I am using the usual arduino rain sensor which relies on the conductivity of water to detect the presence of rain. However only after a few moths of exposure to the elements of nature, corrosion renders the sensor useless. Have a look at this picture bellow :
Another possibility is to use a piezoelectric element. This person used one to turn the kinetic energy of raindrops into LED light:
Maybe a less extreme implementation would be to attach a piezo to a square of roofing tin and use it + an amplifier as a microphone... sample the volume/spectrum on the mic regularly to detect raindrops.
This would have the advantage that you could quantify the intensity of rain, but you might have to do some filtering to reduce ambient noise. It also won't detect moisture as such; damp fog, mist or drizzle might not register, for example.
You could try making your own , there are some optical rain sensors on you tube .
That might show how to use the sensor part in the car one ( my plan B)
LIN bus shouldn’t be hard ... it’s only serial stuff, and similar to CAN .. there is info out there and shields for it too , just not had time to look in detail /find someone who has done it !!
As an alternative , if you made a grid from stainless steel wire and arranged your circuit to :
A) . Only power up and take a quick measurement , say every 5 seconds.
B). After each measurement reverse the power supply to the grid for the same duration to reduce electrolytic action . Have a look at H bridge for the reversing .
A “tipping bucket” sensor makes a simple device for detecting rain. There are probably spare parts for the maplin one on eBay or make one ..
You could try two temperature probes, one exposed and rain and one not. When one gets wet it’s temp should drop slightly. Might need some thought around ensuring even sun and wind exposure.
Good thinking !
Although it sound viable as a principle, I d rather use something proven that works instead of doing R&D on my own!