This is the basic configuration of an operational amplifier sample & hold circuit. The FET and transistor are commonly used. The circuit is from an 80's documentation.
This circuit generates a pulsed tone whose frequency depends on C2 and whose flashing depends on...
This circuit of a Popular Electronics from the 80's selects tones around 60 Hz, acting as a filter...
This circuit samples the current in a load and in case of excessive value it activates a...