This telephone circuit was found on a 90's EDN. It keeps a flashing LED to indicate that there was a call in your absence. The components admit equivalents.
This is one of many zero crossing detector that can be found in this section. It was found in...
This circuit with zener diodes was found in documentation from the 90s. The zener diodes determine the...
Found in a PE Hobbyst Handbook of 1991, this circuit was originally proposed to time photographic...