This circuit was found in a 1966 General Electric documentation. It makes use of direct contact water sensors and therefore requires an isolation or low voltage relay drive transformer.
We found this filter in a documentation for radio amateurs from 1974. The transistors could be the...
An OR gate can be improvised using NAND gates of a 4001 as shown here. The diodes are...
This circuit was obtained in a 1980 publication. The transistors can be BC548 or 2N2222. The...