This simple circuit has good gain and can be implemented with any general-purpose transistor. The circuit is from Electronics Now, June 1997. The coil determines the frequency range.
This is the well-known lightning lamp that was published in the March 1988 issue of Saber...
The CMOS 4046 integrated circuit is seldom used, both due to the difficulty of finding it and the...
What this circuit does is to detect when a signal reaches a certain value determined by the two...