Patent ID: 8796880

Claim:
A system comprising: a power supply ( 110 ) having a power input ( 115 ) and a power output ( 120 ); a first circuit comprising: a first resistance ( 125 ) disposed in, on, or about the power supply, operatively coupled in series with a variable resistance ( 130 ); wherein the first resistance is operably connected to the power output of the power supply; wherein a first intermediate voltage exists at a point ( 135 ) disposed between the first and the variable resistances; wherein the variable resistance is at a maximum value in the absence of an expansion device ( 140 ); wherein the variable resistance is at less than maximum value in the presence of an expansion device; a second intermediate voltage ( 145 ), wherein the second intermediate voltage comprises a fixed voltage signal; a comparator ( 150 ) comprising: a first signal input ( 155 ) comprising the first intermediate voltage; a second signal input ( 160 ) comprising the second intermediate voltage; and a signal output ( 165 ); wherein the comparator signal output comprises: a binary high signal ( 170 ) if the first signal input voltage exceeds the second signal input voltage; and a binary low signal if the second signal input voltage equals or exceeds the first signal input voltage; and an external device ( 180 ) having a signal input ( 185 ); wherein the comparator signal output is operatively connected to the external device signal input; wherein, when the comparator output signal comprises a binary high signal, one or more external device functions are enabled; and wherein, when the comparator output signal comprises a binary low signal, one or more external device functions are disabled.