This circuit provides a signal when dialing occurs. The circuit is powered by the telephone line voltage itself. We found it in an old documentation.
In this circuit, D.A. which is actually O. A. of an operational amplifier, which can be any type...
A narrow range of frequencies around 1 kHz is rejected by the high Q filter shown in the figure,...
This circuit, which uses a planar silicon sensor, is from a 1964 Electronic Design. The component...