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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?

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  • \$\begingroup\$ Is the metal gold plated? \$\endgroup\$ – Indraneel Jan 22 at 21:36
  • \$\begingroup\$ Use a different metal. \$\endgroup\$ – Hearth Jan 22 at 21:37
  • \$\begingroup\$ @Indraneel based off what I'm seeing on Amazon I've seen Nickel used. I was interested in something generally like this should I be looking for gold plated hygrometers? \$\endgroup\$ – Sani Evans Jan 22 at 21:48
  • \$\begingroup\$ those are manufactured by regular PCB etching/milling processes, and I'd bet that they aren't nickel plated, 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. amazon.com/DFRobot_Soil-Moisture-Arduino-Compatible-Immersion/… \$\endgroup\$ – Phil G Jan 22 at 21:58
  • \$\begingroup\$ @PhilG thank you plenty, very informative and points my more general research efforts in the direction they need to be. Would you mind adding that as an answer so I could choose this as the right one? \$\endgroup\$ – Sani Evans Jan 22 at 22:01
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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.

enter image description here

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As an addition to a more robust plating, going from measuring with a DC current to an AC current would lessen the electrolytically induced corrosion, as you would force ions back and forth from both plates.

The moust robust solution thou is to measure the moisture contactless, like a capacitor. Then you can have two plates that are isolated and encapsulated in plastic or anything else that is non conductive and non corrosive. There are lots of both commercial products and DIY solution based on this technique on the internet.

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  • \$\begingroup\$ When I was experimenting with moisture sensors, I used stainless steel probes and reversed the current through these by taking two measurements. The entire process lasted a millisecond, so the induced corrosion was negligible. \$\endgroup\$ – henros Jan 22 at 23:22

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