This circuit was found in Radio Electronics from the 90s. The sensor is an oscillator whose frequency depends on humidity, an uncommon component nowadays.
Found in Linear Technology documentation from the 1980s, this circuit has an accuracy of 0.01%....
This amplifier circuit for listening was found in a book by Hugo Gernsback from 1960. The...
This circuit is from a current regulator up to 1 A, ie a constant current source. The LM320...