This circuit for light modulated in frequency (FM) operating at 50 kHz was found in a 90’s Electronics Now. The circuit has an active filter. Modern equivalent transistors can be used.
This circuit uses a magnetic phone containing 3 germanium transistors. This is a Japanese...
This super metal detector uses three coils, operating in differential form with two transmitter and...
A simple version of VCO CMOS using 4049 inverters is shown in the figure. This circuit can be...