We found this circuit in a 1965 Electronic Design. Transistors are still common but admit equivalents for some of them. The circuit drains a current of only 4 mA.
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...