SoilHumiditySensor

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

Introduction

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.

Hardware

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.

Software

See my github repository.

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