This sensor switches your garden irrigation pump or the magnetic valve on when the soil is dry and switches off when there is enough humidity in the soil. The measuring head has to be buried into the ground at the depth where it shall measure and has to be connected with the basic device via a cable. Approx. 2 m of cable are included, the sensor cable may be increased up to 20 m with normal 2-pole cable. The device is operated by means of a commercial plug power supply (12 Vdc stabilized, > 130 mA, jack plug 3.5 mm). If the garden is to be irrigated at certain times of the day or weekdays only, then insert timer before the plug power supply and program it accordingly. The soil humidity sensor starts to operate when it receives current from the power supply. Operation sequence:The soil humidity is measured after switching on the operating voltage. The connected pump is switched on for 18...30 minutes if the soil is too dry.If the soil is humid enough the device switches to "Pause" for about 18...30 minutes and makes a new measurement after that. This continues as infinite loop until the operating voltage is switched off.