We find this circuit in an Electronics Now. The indication of the logic level is done on a 7-segment display according to the connections given in the diagram.
Found in a 1980s documentation, this amplifier uses an operational aplifier of the time with two...
This circuit was found in a Popular Electronics from the 90's. The frequencies depend on the...
This is a Philips commercial circuit from the 1980s. The circuit must be powered by 28 V and its...