This circuit for multiple sound inputs was found in a Radio Electronics from January 1992. It consists of a Bargraph connected to a multi-input mixer.
This circuit uses two sensors that are placed at the intersection of a miniature railway, causing...
This circuit with RIAA equalization is from 1985 US documentation. The circuit has a flat response...
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....