This circuit for very long-time intervals was found in the March 1993 Radio Electronics magazine. Times of several days or even weeks can be achieved depending on the value of C1.
We found this circuit in the 1983 Radio Electronics Special projects magazine. The components are...
With the presented circuit it is possible to detect signals from transmitters in a frequency range...
This circuit was found in a British documentation from 1969. It can be implemented with modern...