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Project SoilHumiditySensor
Investigation of soil humidity sensors
Status In progress
Contact bertrik
Last Update 2019-05-12


A number of types of soil humidity sensors exist. Many have the problem that the electrodes corrode.

For example, see this video by Andreas Spiess that compares a couple of types.

I got a few probes of the capacitive type, with the electrodes themselves being covered in solder mask.



It got these capacitive ones from Aliexpress.

I've connected it up to a Wemos D1 mini ESP8266 board, as follows:

  • probe GND (black) to Wemos D1 mini pin D5
  • probe VCC (red) to Wemos D1 mini pin D0
  • probe AOUT (yellow) to Wemos D1 mini pin A0

This way, all connections on the Wemos D1 are right next to each other and the wire with the 3-pin connector can simply be plugged into the Wemos D1 mini without having to modify the cable.

The software puts a low level on pin D5 (to emulate GND) and a high level on pin D0 (to emulate VCC). The idea is that the operating current of the probe is low enough for this trick to work.

I put heatshrink wrapping around the top part of the probe, to protect the electronics from moisture.


See my github repository.

The software takes a measurement at a regular interval and sends it over MQTT.