We found this circuit in a 1964 Electronic Design. Transistors can be modern general-purpose equivalents. The circuit converts a 1 MHz sinusoidal signal into a rectangular signal.
Found in old documentation about neon lamps, this circuit shows how to add a simple blown fuse...
This circuit was found in a 1980s documentation. It triggers a relay when liquid from a reservoir...
For counting to values higher than 16, many 4520 can be cascaded as shown in Figure . The EN...