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 a Radio Electronics. The circuit can be seen elsewhere on this site. The...
This circuit is from the 1977 RCA Linear Integrated Circuits Manual. The circuit has a...
Taiyo Yudem SAW filters can be ordered from Mouser Electronics for UMST (W-DMA), GSM, CDMA, LTE,...