This circuit triggers an LED when the input signal exceeds the peak, or the value set in RV1. The transistors can be the modern equivalents BC549.
This circuit was found in an old documentation from Europe. The integrated circuit used is...
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...
This photometer is based on a Wheatstone bridge that must be balanced by the linear potentiometer P1. The...