Patent ID: 7880734

Claim:
A control system comprising: (a) a submodule including: (i) a first input terminal; (ii) a second input terminal; (iii) a first light source having a corresponding anode and having a corresponding cathode, said first light source operative to emit light when said anode of said first light source is positive with respect to said cathode of said first light source; (iv) a second light source having a corresponding anode and having a corresponding cathode, said second light source operative to emit light when said anode of said second light source is positive with respect to said cathode of said second light source; (v) an optical detector operative to detect light emitted by said first light source and operative to detect light emitted by said second light source, and further operative to output a signal upon detection of light, and (vi) two current limiters, and wherein said anode of said first light source is connected to said cathode of said second light source at a first junction, and wherein said cathode of said first light source is connected to said anode of said second light source at a second junction, and wherein a first said current limiter is connected serially between said first input terminal and said first junction and wherein a second said current limiter is connected serially between said second input terminal and said second junction, said submodule being operative to detect a voltage difference between said first input terminal and said second input terminal regardless of polarity; and (b) an interface, and wherein said submodule is operative to be connected to an external device via said interface, and wherein said interface is operative to be connected, at any particular time, to a said submodule chosen from a plurality of said submodules.