Patent ID: 6970752

Claim:
Apparatus for detecting the closure of one of a plurality of switches using a single input line of a detector, the apparatus comprising: a voltage generator configured to be responsive to a switch closure for generating an output voltage on the input line; the output voltage being one of a plurality of predetermined voltages depending on which one of the plurality of switches is closed, wherein the voltage generator comprises a voltage divider having: a first resistance; and a second resistance electrically coupled to the first resistance at a control node, the second resistance comprising a network of resistors connected in series and electrically coupled to the plurality of switches: a microphone for converting sound received thereat to audio-frequency signals on the input line, the microphone being electrically coupled in series with the second resistance of the voltage generator; a comparator in the detector receiving the output voltage on the input line and for determining which one of the plurality of switches is closed; and a storage means for storing audio-frequency signals on the input line when one of the switches designated as a recording function switch is detected to be closed.