an environmental condition monitor configured for simple upgrade from analog signal output to any of a plurality of digital communication protocols . a display board includes the analog signal acquisition and processing elements of the device and also includes a pre - positioned but initially inoperative digital communication output connector . a connector board associated with the display board includes a connector to which any one of a plurality of digital communication boards may be selectively connected , depending upon which of a plurality of digital communication protocols is desired . selective connection of a digital communication board completes a circuit whereby an analog output signal is converted to the desired digital output format and is then communicated back to the now - activated digital communication output connector .