Active audio filter (CB21770E)

This circuit was found in a 1977 documentation for radio amateurs. Integrated circuits are common operational amplifiers.

Full cup detector (CB6956E)
This circuit was found in Popular Electronics. Its purpose is to warn the visually impaired when a glass...
Transmitter for remote control (CB21645E)
This circuit was obtained from a Popular Electronics from January 1967. It has a...
Ultrasonic Transmitter (CB18476E)
This ultrasonic transmitter was found in a 1974 documentation. The receiver is the CIR11753 or...