You can use low cost DIY gypsum sensors, but now also commercial Watermark sensors can be supported
All the programming and documentation is available for free under the GNU General Public License 3.0, and can be downloaded from: https://github.com/ReiniervdL/Vinduino
Printed circuit boards are also available for ordering at cost price:
For the handheld soil moisture meter (Vinduino-H): https://oshpark.com/shared_projects/QWzdU5S6
For the 3-sensor connectivity platform (Vinduino-R): https://oshpark.com/shared_projects/EroKVTqF
Please feel free to share questions, contributions, suggestions, and results with us.
This will help continuing development, and more irrigation water saving!