In use telephone indicator (CB8657E)

Found in a 90s Popular Electronics, this circuit keeps an LED on when a phone is in use. Can be used with extensions.

Comparator with hysteresis (CB9586E)
This non-inverting comparator was found in old American documentation. Formulas next to the...
LED Sequencer 4017 555 (CB25432E)
This traditional LED sequencer circuit was found in the February 1992 Radio Electronics magazine. The...
Series MT Micro Switches
June 2017 - New Honeywell MT MICROSWITCH Series can be ordered from Mouser Electronics for...