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.

2 MHz XTAL Oscillator (CB440E)
This circuit can be used as a clok in digital applications. Power supply is 5-V and the pins for...
Single Pulse Generator 555 (CB13280E)
The MC15555 of this circuit is the old version of the common 555. What this circuit does is...
Laser Sensitive Relay (CB19047E)
This circuit was indicated in an old American publication to serve as a Laser alarm system as a...