The indicator for this circuit is a 0 to 1 mA milliammeter. The operational is from the 70s, when the circuit was published. Modern equivalent can be used.
This simple rain, leak or moisture detector circuit appears in other places on this site with...
This circuit was obtained in a 90s EDN. The components used are from that time. The voltage...
This circuit is from a 1967 General Electric SCR manual. The capacitors are polyester and the...