Found in a 90s Popular Electronics, this touch switch uses a single sensor. PLLs are common today. Observe the supply voltage range.
We found this circuit of a transistor siren in a recent English publication. All components are still...
This 4013 bistable has only a touch sensor that turns the controlled load on and off at its...
This circuit was obtained in a technical documentation from the 70s, but it can be assembled with...