Circuit works Automatic water valve circuit of the farm by the power circuit , detection circuit and control circuit , as shown in Figure 4-157 . Power circuit from the power transformer T, rectifier diode VDl-VD4 and filter capacitor Cl so on. Detection circuit from the high water level detection electrode a, b and the low water level detecting electrode into the water pipe detection electrodes within the c etc. . Control circuit by the time-base integrated circuit IC, relay K and the composition of the external components . IC 2 feet (low to trigger side ) and the low water level detecting electrode b connection , 6 foot (high trigger side ) and the high water level electrode a connection , 4 pin ( reset port ) and the inlet pipe connected to the inner electrode c , d points and tank Metal into the water body and connected . When the tank water level below the b point , IC 3- pin output high , so that relay K work , the work of solenoid valve power , water began to water ; when the tank water level higher than a point , IC 3- foot change Is low , so that power relays and solenoid valves to stop water . When the water into pipes in , IC 4- pin is low , so that IC reset , the 3 -pin output low , relay K and solenoid valve not working . In order to avoid air bubbles inside the pipe , the solenoid valve will repeatedly pass, and set off for the delay capacitor C3 . Components Selection Rl-R3 use 1/4W or 1/8W metal film resistors . Cl choose 22OµF, 25V aluminum electrolytic capacitor ; C2 use 0 · lµF monolithic polyester capacitor or capacitors ; C3 use 10µF, 16V aluminum electrolytic capacitors . VDl-VD5 are selected 1N4001 or 1N4007 type silicon rectifier diode . IC type used when the base NE555 integrated circuit or other types of similar products . 100 K a small selection l2V flow relay . T use l2V ,3-5W of power transformer .