This circuit implements two logic functions at the same time. The diodes are for general use and the resistors have typical values of 2k2 for logic of 5 V.
The circuit is suitable for calls in a residence and was published in the Radio Electronics...
The input impedance of this circuit is about 700 k ohm and the output impedance is about 1 k ohm....
With the values of the components indicated, the circuit generates a 1 kHz signal. The power...