Patent ID: 8907523

Claim:
An apparatus comprising: an electrical interface; a signal source operable to output a reference signal via the electrical interface, in which the reference signal is a direct current (DC) signal; a first light source; and a logic circuit operable to: receive, via the electrical interface a first signal indicative of a response to the reference signal; determine a second signal based on the first signal, in which, in determining the second signal, the logic circuit is operable to: measure the voltage differential across a resistive element of the signal source; determine a first value of the second signal if the measured voltage differential is zero, in which the first value of the second signal is a value that instructs the light source to not emit light; and determine a second value of the second signal if the measured voltage differential is non-zero, in which the second value of the second signal is a value that instructs the light source to emit light; and transmit the second signal to the first light source.