This circuit was found in a Radio Electronics from 1970. The coupler with LDR is from that time, but the circuit can be adapted to use modern components and act as a shield.
This is a very simple atomic radiation detector circuit using a Geiger-Muller tube. The circuit was...
With a 120 ohms resistor this circuit can also be used as a shield for 3.3 V output voltages. The...
This is one of the many universal motor controls that the reader can find on this website. The...