Here has been presented low cost versions of detector of levels of water. Works on the same principle as well as LM1830, but is the price much low cost (although has higher parts). The active output level is 0V. Version can reduce prices the ejection 74HC14, diodes BA157 and outgoing filter 100K-1uF. Thus get the unprotected entry circle, unstrained exit circle of the this active high exit level. In the area when has been detected the voltage close threshold detections, outer disturbances additionally will modulate the exit voltage and about that needs pay attention. If the exit has been intended for the alone signalization then the twinkling in the marginal area and is not so much importantly. However, if want the reliable signal, then recommend the usage of filter and schmitt triger complex (e.g. 74HC14) outbound LM567.
Complex has been checked and work great. Lengths of conduits to electrodes is not critical and may be 10 meters (the senller or the low capacitance koaxial cable). For electrodes use the stainless material (procrom).