I'm building this mostly finished hydroponics system. It's a surge tank build.
Surge tank looks like:
(that's nutrient water, it's got electrolytes that plants crave)
Inside that bucket are two simple reed float switches (these to be exact) to detect water level. They're open when the float is up and closed when the float is down.
I'm using raspberry pi's internal pull-up resistors on those gpio pins that go from the pi to the switch to gnd. I think they're like 50k ohm? That's what people online say, the datasheet is does not specify. Pi gpios are 3.3V rated.
So the pullup resistor basically connects internally such that when the switch breaks the circuit (open), the internal resistor is overcome and the pin reads as 1. When circuit is closed, current flows through the switch into gnd, so the pin will read 0 to the pi.
The submerged (bottom) switch gpio keeps frying no matter what gpio I use after a few days. (confirmed to fail tests with pigpio ./gpiotest, all pins were passing tests before the project). This is the second pin fried in a week and it seems to happen after a few days of stable usage. The top one has been fine for 2 weeks and counting. The only thing I can think of is the bottom switch is submerged and therefore open more often which would mean the current is flowing internal in the pi a lot? Meanwhile the top sensor is closed to gnd more often? Could leaving an open gpio in pullup mode for a while really just fry it? Is the wire picking up stray signals? Electrostatic? I have no clue why these pins are frying. Would a short with the water even do anything?