This two-transistor circuit was found in the September 1971 issue of Radio Electronics magazine. The sensor is an NTC and sensitivity adjustment is via R1.
This circuit was found in a 80s American documentation. The zener diodes determine the points of...
This circuit is from an old manual, but can be easily assembled as the integrated one is still...
In fact, the 556 consists of a double 555, which can be replaced by these integrated ones. The...