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.

Phototransistor Detector (CB24484E)
A first circuit that uses a phototransistor as a detector and is suitable for covering short...
Direction indicator (CB21354E)
We found this circuit in recent English documentation. The circuit uses CMOS technology and can be...
555 Car Alarm (CB3990E)
We found this circuit in an old Mullard (Philips) documentation on the 555 and 556 integrated circuit...