I’ve just found the simple soil moisture sensor on Seeed (seeedstudio.com/wiki/Grove_-_Moisture_Sensor). I’d like to suggest/request some improvements to its documentation:
- Document that it’s a simple resistive soil moisture sensor that’s sensitive to soil composition and salinity, so it needs soil specific calibration;
- Document the rationale behind using the transistor*; and
- Make the resistor values easier to read on the spec sheet **.
- Is the idea to give you a more readable signal along a long cable without having too much current across the probe (and thus too much electrolysis)? Few simple resistive designs use a transistor, so I’m curious about why this does.
** Are those 100 ohm resistors? Wouldn’t that make a short across the probes potentially “interesting”, especially with the NPN transistor essentially switching one of them out of the circuit when its shorted across the probes?
Also, what PCB materials are used? The feet don’t look like copper in the photo.