The figure shows how to use CMOS inverters as amplifiers. The circuit is from a Radio Electronics from April 1984. The supply voltage can be between 3 and 12 V.
With the shadow over the sensor, it is possible to interrupt the sound of your amplifier using this...
This circuit provides a signal when dialing occurs. The circuit is powered by the telephone line...
We found this circuit in a 1995 documentation. It can measure frequencies from 100 kHz to over 100 MHz...