This circuit was found in the August 1972 issue of Radio Electronics magazine. The circuit generates 4 types of signals as can be seen in the diagram. The maximum frequency is around 20 kHz.
We find this circuit in an American 80's documentation. It makes use of IC sensor which is mounted...
This is a configuration obtained from an old manual, using an operational amplifier of the time....
In the figure we have the way to add hysteresis to an operational amplifier. The relationship...