This sensitive circuit was found in the June 1995 Electronics Now magazine. R1 can be from 10k to 1M depending on the desired sensitivity. Power is supplied by the relay.
Found in an Elektor from the 90s, this circuit is based on components that are still common today....
This circuit was found in a Signetics documentation from the 1980s. Next to the figure are the...
This timer of 10, 25, 45 seconds and 5 minutes has its times selected by the keys. The circuit drives...