This 1969 Mullar circuit appears elsewhere on this site. The circuit uses germanium diodes and the indicator is microammeter with zero in the center of the scale.
The CMOS 4060 integrated circuit consists of a frequency divider counter with internal elements...
We found this circuit in a 1983 publication. It is a simple touch alarm circuit using a SCR type...
This circuit is from a Popular Electronics from the 90s. The integrated circuit admits equivalents...