The sensor used in this circuit is uncommon today, however equivalent types can be tried. The comparator also supports modern equivalents. The circuit is from 80's documentation.
This circuit was obtained from a Radio Electronics in May 1967. The circuit consists of a system...
This simple two-transistor capacitance meter uses a 50 uA microammeter as an indicator instrument. The...
Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to...