Serial switch with PIN diode (CB21257E)

This circuit was found in a Popular Electronics from the 90's. The circuit is connected in series.

Wien Bridge Oscillator MC1776 (CB4498E)
The integrated circuit used in this project is not common today, but it can be implemented with more...
Digital signal isolator (CB8021E)
Found in an American publication from 1969, this circuit can be adapted to be used as a shield....
Ammeter (CB9660E)
This current meter with many scales was found in a 80s American documentation. The operational amplifier...