In the figure we have a simple way to have a peak bargraph indicator. The amplifier is of the audio type, but operational ones can be used. The circuit is from Radio Electronics from March 1980.
This circuit uses half of the LM158 operational double but can be used in the series as the LM258,...
This circuit generates audio tones in a speaker with controlled frequency and volume. The...
This circuit was obtained from an article in Radio Electronics magazine in October 1966. It...