This circuit takes advantage of the noise generated at the reverse biased junction of a germanium diode. Other types of diodes can be used. The signal is weak.
This proximity (capacitive) alarm triggers a relay that, in turn, triggers an audible warning...
This sensitive circuit was found in old documentation. The SCR can be any of the 106 series and...
This traditional multivibrator configuration uses an LDR as a sensor. The circuit emits sound when...