Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the frequency of the emitted sound is determined by R1 / C1.
We find this circuit in a 1980s documentation. The circuit uses uncommon components today which can...
We found this circuit in a 1977 Radio Shack documentation. The circuit should be powered, for...
With the circuit shown in the figure it is possible to digitally control the gain of an...