The heat of summer. The sky is cloudless. Without irrigation the garden can not be saved. In this case, it is good to use a plant that waters itself. The device is an electronic relay on the transistor VT1, the base and the emitter of which is connected to the plates of conductive material stuck in the ground at a distance of 3 — 3.5 cm from each other. Because raw land has a low resistance, it can be considered that the base of the transistor is directly connected to its emitter (the transistor is closed). But as soon as the soil begins to dry, a semiconductor device is opened, and actuates electromagnetic relay K1 and its contact pair completing a circuit of the actuator of the electromagnet, lifting the flap of the water tank irrigation.
An electromagnet is a solenoid pull-in action. The coil bobbin is made of a PCB or hard rubber, and has a length of 100 mm, outer diameter 30 mm inner — 20 mm Cheeks with a diameter of 70 and a thickness of 5 mm made of the same material as the frame and glued thereto by glue BF-2 or “Moment”.
Solenoid coil contains 4300 turns of wire sew 0,4 (for mains voltage 127 V) or 5500 turns of PEV 0,35 (for 220V). The core is made from mild steel (steel 10 or 20) with a diameter of 20 and a length of 100 mm. attached To the core pin, the length of which depends on the distance between the solenoid and the valve of the tank. Spring — pusher; its purpose is to at the end of the irrigation to return the flap to its original state.