Problem
A customer came to AO for a rugged multi-channel data logger and controller for use in the HVAC industry for monitoring operation of heating and cooling systems. It had to be programmable to allow custom monitoring protocols to be used, but it had to operate stand alone for long periods.
Solution
We designed a unit that had analog inputs, reference voltage outputs, digital I/O and digital pulse counter inputs. It communicated with computers through a RS-232 serial interface. Connections were made through a front panel jack array that accepted the "banana" jack connectors in common use. It was powered by two +6VDC lantern batteries or an external AC power supply, with two C cell backup batteries to retain data after the larger batteries were depleted.
The unit was packaged in a rugged plastic case with an easily removable back panel for battery access. The circuits were designed with the through-hole DIP IC technology in common use at the time. This required multiple circuit boards to fit the circuit inside the small electronics package. The boards were stacked on the front jack panel and bussed through a ribbon cable "backplane." The assembly was housed in two aluminum subassemblies that fit into an attractive off-the-shelf package.
Results
Two versions of the product were developed. The DATREX unit carried fourteen sets of analog inputs and +5VDC reference outputs, eight digital I/O ports, six digital inputs and three pulse counter inputs. The lower cost DATREX II had 8 sets of analog inputs and +5VDC reference outputs.