The frequency of this circuit, for the indicated components, is 1 kHz. Other operational amplifiers can be used, and the power supply must be symmetrical.
We found this circuit in a Motorola manual. The circuit employs operationals that are uncommon today...
In the figure we have the way to use a voltage comparator powered by a voltage to control a...
CTS IoT Quartz Crystals Available through Mouser Electronics, CTS quartz crystals are especially suited...