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.
The purpose of this circuit is to increase the sensitivity of a common multimeter in its voltage...
This is the modern version of the Galena radio in which the detector is a germanium diode (which can...
This circuit allows the measurement of very weak currents indicated on an analog instrument or...