In this circuit the LED lights up when the voltage drops below the value set in the trimpot. The transistors can be the BC548. The circuit is from a 1999 American publication.
This circuit was found in 1968 General Electric documentation. The circuit uses components from the era...
This instrumentation amplifier uses three operational ones, and the components must maintain the...
This circuit doubles the frequency of a rectangular signal applied to its input. The circuit has a...