This oscillator was found in the January 1987 issue of Radio Electronics magazine. The frequency is adjusted by C1, and the output has good symmetry. The power supply is typically 3 to 12 V.
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...