Dear Koepel,
Thank you very much for advice.
Open source was already published earlier on: GitHub - greensensors/SMT-Soil-Moisture-Sensor-for-Arduino: Soil Moisture & Temperature Sensor.
SMT-01 device is simple and has two main components: 2N2222A - as Нeater and DS18b20 - as Thermometer.
For this reason, the sensor is inexpensive but gives good and stable measurement results.
I have previously tried other methods of measuring soil moisture for the home garden, but this sensor turned out to be the most acceptable. And I thought that maybe this sensor will be of interest to the community. If there is interest, then I think it will be easy to manufacture the required number of sensors.
If you are interested, I can provide additional information on this topic.