This circuit from the 90s, found in an Electronic Engineering can be used as a shield since its control is digital with TTL logic of 5 V. The components used are still common today.
This different configuration for a crystal galena radio or modernized since a diode is used, has a...
This circuit is from 1990 documentation. When we press D1 the lamp remains on for a time interval that...
This version of the test lights a lamp when the ring touches the tortuous wire. The SCR can be the...