Context: I'm working on a gardening project using a microcontroller to power grow lights and other related components after I've built on top of it.
Case: I was interested in adding some hygrometers to detect their moisture levels rather than guess-timating when it'd be appropriate to water them.
Issue: One design issue I've seen repeatedly when researching the subject: if hygrometers are used to detect moisture levels in soil over prolonged periods of time, the metal will begin to corrode causing accuracy/sensitivity issues.
Q: Is there a way to prolong their life to prevent corrosion+retain accuracy, or some tips for instrumentation people may not be following? Would a hygrometer be the sustainable solution here considering the Case and Context?
Best Answer
Those sensors are manufactured by regular PCB etching/milling processes (cheapest way of manufacturing something like this), and I'd bet that they aren't nickel plated (not a commonly offered finish), more likely tin, but in any case they won't 'rust', as the underlying traces are copper, but will corrode over time, or at least develop an oxide layer that reduces the conductivity indicating that the soil is dryer than it really is.
Gold plating would help, and they are available. Gold plated boards are substantially more expensive than tin.
Here's the first one I found.