This electronic Morse key was found in a Popular Electronics from the 90's. The components are common, but there is a mechanical part that requires assembly skills.
The circuit with a common operational amplifier uses a zener as a reference. The circuit is from...
This circuit was found in a 90’s Popular Electronics. The circuit is used to analyze noise in...
This 1989 circuit activates a protection relay if one or two phases are missing from a three-phase...