Patent ID: 8548126
Filing Date: 2013-10-01
Classification: H04M

Abstract:
1. An emergency telephone handset, comprising: a microphone input; a polarizing diode coupled in series with the microphone input; and a resistor coupled in parallel with the polarizing diode and in series with the microphone input and having an impedance, wherein the microphone input, the polarizing diode and the resistor are configured to be coupled with external telephone wiring that can be polarized by a telephone control panel circuit; wherein, when the telephone handset is coupled with the external telephone wiring, the telephone control panel circuit differentiates between a shorted wiring and a call-in signal based on operation of the resistor and the polarizing diode by measuring the impedance at the telephone control panel circuit, wherein a first impedance of the measured impedance corresponds to a shorted wiring and a second impedance of the measured impedance corresponds to the telephone handset coupled to the external telephone wiring corresponding to the call-in signal, the second impedance is higher than the first impedance due to the effect of the resistor; and wherein the polarizing diode facilitates operating a telephone station with a 3-state central telephone panel and operating the telephone station with a 4-state central telephone panel, the resistor and the polarizing diode operative to permit the telephone handset to operate with a 3-state telephone control panel when a voltage having a first polarity is applied to the telephone station or with a 4-state telephone control panel when the voltage having a second, opposite polarity is applied to the telephone station, wherein said second, opposite polarity causes the polarizing diode to shunt the resistor by bypassing the resistor when the 4-state telephone control panel applies the voltage having the second, opposite polarity.