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.
We found this circuit in Radio Electronics Special Projects from 1992. The circuit turns on the...
We found this circuit in the Texas Instruments' Linear Circuits Applications. It uses an...
This capacitive sensor that operates with a high frequency oscillator was found in Radio...