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I haven’t used one of those before, but it outputs a square wave that’s frequency is proportional to the soil moisture, so your logger would have to do some frequency measurements and then convert that to VWC using a formula. But that particular sensor has a low (0.7v) output, so you’d probably want to use the CS625 sensor, which is the same as the 616 but has a 3.3v output, which is what the Mayfly would want to see. The sensor needs 5v excitation though, but the Mayfly can provide that if you switch over the jumper. Most of the frequency-counting libraries for Arduino use interrupts, so you’d probably want to use the D10 hardware interrupt pin for reading this sensor. It might also be easier to use a separate frequency-to-voltage chip to do the frequency measurement offboard and simply read the chip’s output voltage with a Mayfly analog pin. Note that the sensor has a maximum VWC of 50%, and I’ve seen levels higher than that in many of my deployments. Are you using this sensor somewhere where you don’t expect high moisture levels? There are other sensors from other manufacturers that cover a wider operating range and have a much more convenient digital output if you’re willing to consider other hardware options.