Moisture sensor PCB design questions

[nglessner]

I'm starting to design a similar project to yours and have lots of questions - I'll create a discussion for reach major topic.

First off is the moisture sensor PCB - what are the requirements for this?
Is there a required PCB thickness? is HASL ok? ENIG?
Is PCB color important?
Is there a design problem with just using "gold finger" edge connectors instead of the 2x5 pin header? I'm wondering if the gold finger edge connectors wouldn't provide enough mechanical support... The design I'm hoping to use should be as water/dust proof as possible, since I hope it to go outdoors.

[ovidiu4]

Hi!
I am by no means an elecrical engineer or PCB designer, this is just a hobby for me.
So please don't be surprised to learn that some decisions I took were just random :)

Regarding the soil probe I just used the default config from JLCPCB.
I did not test other variations but everything should work just fine, the touch sensor of the ESP32 is really sensitive.

• 1.6mm thickness
• Black color
• HASL
• PCB edges covered with nail polish

I initially wanted to use edge conenctors since they seem more robust but i gave them up for simple 2.54mm pins just because they were taking too much space inside the case.

You could make it water proof but you'd have to redesigning the case since i left some big holes in it for ventilation. Keep in mind that temps and humidity might get high inside the case if you make it watertight.

If i were you, i'd just stick the case somewhere where water cannot get to it and just extend the pins with wires to the soil probe. You don't actually need all 10 wires

[nglessner]

Waterproof is probably taking it too far. Waterproof "enough" is what I'm hoping for. Here's what I'm aiming for at the moment. A simple board like below, combined with your idea of a super-simple PCB for the capacitive moisture sensor. I'll use a Hammond 80x40mm water-tight enclosure and have to cut a slit in it for the insertion of the sensor PCB. Maybe some hot-glue or something to help close that up for weather/dust/bugs.

[nglessner]

For calibration of your sensor - did you just measure what "dry" was and what submerged was and use that as your range?

[ovidiu4]

For calibration of your sensor - did you just measure what "dry" was and what submerged was and use that as your range?
Basically yes :)