I’ve now got the rain gauge down and taken it apart. Possibly I’ve posted photos before, but this is what the guts of it look like:
After ungoo-ing the PCB, I’ve come up with a first approximation of the switching part of the circuit which I have drawn, in true engineering fashion, on the back of an envelope.
The reed switch fell apart as soon as I touched it, so that’s definitely one problem to sort. The fact that there’s a dead battery welded to the PCB isn’t that helpful either. I may clip that off and replace it with something more maintainable. There are perhaps some other things that could do with tidying up too. I’ll ponder on those. Meanwhile, as I have most of the circuit worked out (I think), perhaps I should finish the job and draw it properly.