Found in a Popular Electronics from the 90s, this circuit uses common components with several operational options, including the use of an optocoupler that allows its application in a shield.
This circuit is intended to trigger an alarm when the input voltage exceeds one value and to...
This source was found in a 1982 American publication, but can be easily assembled using 2N2995 (PNP...
This circuit, obtained from the component manual used, has an ultra narrow 1 kHz range given by...