This 555-based circuit was obtained from the 1995 Encyclopedia of Electronic Circuits volume 5. It triggers an SCR when the transistor is cut off.
In the figure we have a bistable multivibrator using an operational one. The circuit is from old...
This is another of the Star Trek red alert circuit that you can find on this site. We took this...
This circuit for testing zener diodes by lifting their curve on an oscilloscope was presented in...