Contact Sense Multiplexer for Long Line Use
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
This arrangement monitors a plurality of alarm or like contact sense devices connected to a Central Processing Unit (CPU) over a single pair of voice-grade communication wire lines at minimal cost. A Time Division Multiplexing (TDM) circuit is utilized at a remote location to the system, and timing is controlled by a two-phase clocking circuit. The clocking circuit steps a counter which in turn provides binary address signals for operating the multiplexing circuit. When an alarm is noted, the pertinent address is transmitted to the TDM as a standard Dual Tone Multiple Frequency (DTMF) signal over a pair of voice-grade conductors. Thereafter, it is demodulated by a DTMF detector, and coupled to the DI or CI points of the CPU by an optocoupler device.