This circuit is from a 1968 publication. Here we have several types of resistive sensors with individual adjustments triggering a single SCR. Power depends on the type of sound device to be triggered.
This conventional window comparator configuration was found in an old documentation. It is valid...
This circuit is a from publication 1980, but still can be mounted with BC548 transistors for Q1...
This shield circuit for PC was found in an English documentation from 1996. The current of the...