US 4,398,147 A · Methods of testing multifrequency dialing signals

Abstract

A predetermined sequence of multifrequency signals are fed to a multifrequency dialing board (24) and are separated into their component signals by high and low filter circuits (50 and 52). The component signals are converted into (1) square wave signals by zero crossing detectors (54 and 56) and (2) d.c. signals having amplitudes proportional to their respective frequencies by converters (72 and 74). The d.c. signals are then converted by analog-to-digital converters (80 and 82) into digital signals having values equivalent to the amplitude of the d.c. signals. A microprocessor circuit (60) monitors the digital signals to determine the amplitude of the signals. The microprocessor circuit (60) determines the frequency of the component signals by monitoring the time required for eight cycles of the respective square wave signals. The microprocessor circuit (60) also facilitates the self-calibration of the multifrequency dialing board (24) which ensures the correct operation thereof in the event of an error due to temperature or aging components.

Claims2

Dependent claims

A method of testing the frequency of a signal, which comprises the steps of:

(a) feeding a standard signal having a known amplitude through a signal preparation circuit to determine any gain or loss in amplitude as the signal is being fed through the signal preparation circuit;
(b) processing an unprocessed signal through the signal preparation circuit wherein the unprocessed signal is being prepared to test the frequency thereof;
(c) adjusting the amplitude of the processed signal by an amount equal to the determined gain or loss of the amplitude of the standard signal;
(d) determining whether the adjusted amplitude of the processed signal exceeds a predetermined threshold amplitude value;
(e) measuring, from a precise time of the unprocessed signal, the time interval required by a preset number of cycles of the unprocessed signal, in response to the determination that the adjusted amplitude of the processed signal exceeded the predetermined threshold amplitude value, to provide an indication of the frequency of the unprocessed signal;
and
(f) comparing the measured time interval with a preset time interval to provide an indication as to whether the frequency of the unprocessed signal is an acceptable frequency.

4 more elements

Dependencies are inferred from the claim text.

Methods of testing multifrequency dialing signals

Life of this patent

Methods of testing multifrequency dialing signals

Life of this patent

Abstract

Claims2