US 31347502 A description one embodiment of the present invention includes an addressable i o board for extending i o for one or more programmable logic controllers plc that are insertable into the board fig1 illustrates a sectional assembly of figures tbd into an overall schematic of the embodiment the discussion that follows the sections of the schematic as illustrated in fig1 1 through 1 3 the board includes sixty digital input lines i 1 i 60 each of the digital input lines are associated with a light emitting diode led d 61 d 120 and biased with a input voltage through a resistor r 61 r 120 the bias is such that an led associated with the particular input lights when the input is grounded in addition the board includes sixty analog input lines i 1 j 1 a a 15 j 1 a i 1 j 1 b i 15 j 1 b i 1 j 2 a a 15 j 2 a and i 1 j 2 b i 15 j 2 b the analog inputs are accepted via an associated 15 pin d connector j 1 a and b j 2 a and b as illustrated in fig1 4 through 1 7 the inputs are isolated via a group of opto isolators u 1 u 16 the outputs from the opto isolators u.