Ultrasonic Proximity Sensor (CB21312E)

This circuit was found in a Popular Electronics from the 90s. The circuit uses a ceramic capsule as an emitter and detector.

Current to voltage converter (CB7332E)
This circuit is from a Popular Electronics from the 90s. The integrated circuit admits equivalents...
Hall Lamp Timer (CB16406E)
This very interesting project was obtained in a 1980 publication. It consists of a device that is...
Freezer Alarm (CB1281E)
This circuit beeps when the sensor is triggered by the opening of the freezer door or other...