We find this circuit in an Electronic Design of the 90s. The used integrated circuit admits equivalents and next to the diagram are given the formulas for the calculation of the components used.
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...