Imported from GitHub: Incomprehensible/Mad_PlantBug · commit a7fc232 · license MIT

Description

DIY and open source soil moisture sensor 🪴

README

Mad_PlantBug

Low-power capacitive soil moisture sensor with BLE connectivity.

Features

• powered via CR2032 coin battery
• transmits telemetry via BLE
• measures ambient light and temperature
• visual indication via LED

Top	Bottom

How it works

This sensor determines the amount of soil moisture by measuring changes in capacitance of the probe submerged in soil.
Insertable part forms a parasitic coplanar capacitor which uses soil as a dielectric medium.
As the environment around the capacitor changes depending on whether the soil becomes wetter or drier, so does it capacitance.
Together with a resistance the probe forms an RC low-pass filter.
Changes in capacitance shape the output waveform observed by the sensor.
Measurement pipeline logic is as follows:
environment changes -> capacitance changes -> cutoff frequency changes -> peak amplitude changes

Capacitance measurement

• Clean PCB measurement in air: ~59pF
• Fully submerged in water: 2nF

Current issues

• CR2032 footprint and power pins connection is incorrect.