Telephone ring detector

A telephone ring detector for detecting a ring signal voltage, said ring detector comprising:

• a ring signal coupler having a blocking capacitor outputting said ring signal voltage to a current limiting resistor in series with said blocking capacitor;
• a voltage threshold setting device in series with said current limiting resistor, said voltage threshold setting device comprising a first zener diode in series with a second zener diode, each said zener diode having a voltage value of 39 volts;
• an opto-isolator in communication with said voltage threshold setting device, said opto-isolator providing an output signal when said ring signal voltage is above said voltage threshold;
• a microprocessor responsive to said opto-isolator, said microprocessor including a timer for measuring a time duration of said output signal of said opto-isolator, said microprocessor comparing said time duration with a preselected time interval value being less than 50 milliseconds, said microprocessor outputting a ring detection signal when said time duration exceeds said preselected time interval value;
• and
• a line switch having at least two output lines, said line switch receiving said ring detection signal from said microprocessor and directing communication signals to one of said at least two output lines.

A method of detecting a telephone ring signal comprising:

• detecting a ring signal voltage;
• comparing said ring signal voltage to a predetermined threshold voltage;
• providing an output when said ring signal voltage exceeds said predetermined threshold voltage;
• measuring a time duration of said output;
• comparing said time duration to a predetermined time interval;
• and
• providing a ring detection output signal when said time duration of said output exceeds said predetermined time interval, said predetermined time interval being less than a ring cycle.