robtillaart:
@2: you don't need an extra hole, on contrary I would propose a small compressed C02/air cylinder, a valve and a pressure sensor and some bits to control it. Yes it means some additional electronics. After the cap is closed the valve opens to raise the inner pressure by X%. If there is any leakage wherever it will be detected in contrast of just detecting a switch has been pressed the right way.
Additional, if there is a very small leakage some overpressure might prevent water leaking in (keep it local)
I like it, the cylinder would have to be fairly large though, not sure how many trips it would take before i would have to swap it out. It is most certainly something to ponder. I am not sure about any issues that could come about with submerging a compressed air vessel though. I suspect it wouldn't do anything really because it's a maintained 1 atmosphere of pressure inside the container regardless of depth.
robtillaart:
Hard to know what PeterH had in mind but a lever microswitch held such that the rod passing it deflected the lever would be a very basic way:
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| |An optical path broken by the rod would be another way.
Also a good idea. would probably use some of the same hardware but still serve the purpose. will add it to the possible list as well.
This is good stuff guys. Thanks a ton. I tend to over think things..... elegant solutions are the best but i am always severely lacking in those.
Keep em coming.