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 the Texas Instruments opto-electronics manual. The button resets and the...
This circuit is from a 1992 documentation, but the components used can still be easily assembled. The...
This interesting amplifier for frame antenna for the medium wave range was found in a Popular...