Based on the LF256 operational amplifier, this circuit was found in the September 1989 issue of Radio Electronics magazine. The indicator is analog, and the power supply must be symmetrical.
August 2016 - It can be obtained from Mouser Electronics thenew broadband ADCs ADS127L01 from...
This circuit takes advantage of the noise generated at the junction of a zener diode of any type....
This circuit was found in Motorola documentation from 1968. Transistors can be modern equivalents, just...