A soil moisture sensor detects the level of moisture in the soil, to enable informed decisions to be made by smart irrigation systems.
We tested these cheap soil moisture sensors and whilst they worked initially, they use a dc voltage to measure resistance and this causes them to fail quite quickly.
After just a few weeks use, the metal probes will stop working due to galvanic corrosion. You can see the metal part of the probe has gone, resulting in the sensor reporting that the soil is dry when it is not. The copper that has dissolved in now in the soil in the plant pot and this is not a good thing for most plants.
To resolve this issue we developed our own soil moisture sensors using an ac voltage for detection and with A4 stainless-steel probes. These will be available to purchase soon.
For deeper soil and plant pots, the probes need to be quite long, to ensure they are not just sitting in dry soil at the surface. The length of the probes will affect the readings and if the probes are too long, the soil at the surface could be allowed to become too dry. Our sensor can support probes that are up to 1m long.
Typically we model soil moisture as a percentage, where 0% equates to bone dry and 100% equates to fully saturated. We normally take readings from soil moisture sensors every 19 minutes because it changes very slowly (unless an irrigation pump has been active) and we check whether irrigation pumps should run at a much longer interval than this.
These types of soil moisture sensors can often be used as flood sensors and even water level sensors but the cheaper versions will corrode quickly if left in a liquid.
We couldn't find a soil moisture sensor that met our requirements, so we developed the Smartisant soil moisture level sensor.
Whilst we mainly designed the Smartisant soil moisture level sensor for indoor irrigation applications it is resin encapsulated and waterproof, so it can be used outside too. We have a custom prototype in use in our front garden with extra long leads, with colours chosen to blend into the soil. We have also painted it green to make it less visible.
