Low-power capacitive soil moisture sensor with BLE connectivity.
- powered via CR2032 coin battery
- transmits telemetry via BLE
- measures ambient light and temperature
- visual indication via LED
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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
- Clean PCB measurement in air: ~59pF
- Fully submerged in water: 2nF
Assembly & measurements
