This circuit synchronized by the power grid can be used as a shield. We found it in an 80's Electronic Engineering. R1 can typically be 4k7.
This circuit is from a 1976 Motorola CMOS manual. It can be implemented with modern Darlingtons like...
In the figure we have the way of modulating or controlling the frequency of a relaxation...
The purpose of this circuit is to monitor the operation of an alternator in cars with a 12 V...