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 appeared in the June 1990 issue of Radio Electronics magazine. Integrated circuits must...
Lockout shooting, due to the incidence of light, can be achieved with the circuit in the figure. In...
This circuit can function either as a crystal or galena receiver with a pre-amplifier using a FET...