Found in a 90s Popular Electronics, this circuit provides sinusoidal signals at frequencies given by the components, as shown in the table beside the circuit.
This circuit uses a CA3140, an operational amplifier with FETs in the input stages. Equivalent can be...
This circuit is indicated to operate from high impedance sources as piezoelectric transducers....
This circuit also detects IR, providing LED indication. The circuit is used to indicate humidity in...