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I'm using "Aquarium Hydroponic PH Electrode Probe/Liquid PH Value Detection Sensor" on ebay for $36 with probe. It even came with example code.

I'm using it for a basic application and only roughly calibrated it with paper tests using tapwater and vinegar. I'm only measuring between ph 5-8 and my application doesn't really require precision.

I only found one soil pH sensor on Adafruit, but it's currently sold out:

https://www.adafruit.com/product/4026

That's a capacitive moisture sensor. It is incapable of measuring pH.

Oof, you're right of course. My bad! Thanks

I picked this sensor somewhat randomly on Aliexpress and it seems to work well (with calibration on both, tracks closely to my commercial Nutra-Dip Trimeter).

For hydroponics (where 0.1 pH is plenty of precision and pH range should be inside 5-8), I was quite happy with the $14 version below.

https://www.aliexpress.com/item/32957428276.html?spm=a2g0s.9...