Electronic – arduino – How to measure moisture on a conductive flat surface as an analog/digital value


So as the title states, the question is:

Is there a way to measure moisture on a electrically conductive flat surface?

Optionally, it would be great if I could have an indication of the amount of moisture on the surface, preferably as an analog value, so I can read it via an Arduino (when I say how much, I do not need it in like mililiters, just a higher or lower value representing moisture).

Just to give some context:
I am working on a project to cool down a laser module using Peltier elements (TEC), and I want to know when moisture starts to form around the laser diode as a preventive safety feature, because water is not good for lasers diodes 🙂 I am aware that I could just monitor the dew point, still, I am interested if this is even possible or not.

Thank you.

Best Answer

I agree that measuring dew point is likely easier (buy a humidity sensor and do a bit of math), but if you want to measure condensation, consider using capacitive sensing.

Water has a dielectric constant much higher than that of air, so the capacitance between two plates will be higher if there is some water between them rather than merely air. (If the water is impure and therefore conductive, it instead reduces the effective distance between plates, also increasing the capacitance.) This is the technique commonly used soil moisture sensors.

Measuring capacitance can be done in many ways: I might use a hysteresis oscillator.

Note that you will need two conductive plates for this technique, not merely one, but they can be coplanar rather than parallel if that is easier to arrange.