Apparatus and method for incoming call detection and alarm circuitry for cellular telephones

摘要

An apparatus for use with cellular telephone to indicate an incoming telephone call to a user includes a cellular telephone battery pack having a circuit that generates a voltage signal with a value representative of the current being drawn from the battery by the operation of the cellular telephone. A status determination circuit monitors the voltage signal and generates a powered up state signal whenever the value of the voltage signal increases from a first selected lower value to a first selected higher value for a first preselected period of time. An incoming call detection circuit whenever the powered up state signal is present and either the voltage signal is representative of a selected periodic current transient in the current being drawn by the cellular telephone for a second preselected period of time. An alarm is operative upon receipt of the alarm start signal for indicating an incoming call to a user. Also a cutoff circuit monitors the voltage of the battery and disables the apparatus further operation whenever the battery voltage drops below a preselected cutoff value to avoid damage to the battery.