Portable Input/Output Instrument For Interfacing Student Digital System Designs

Any digital system must include some capabilities for input of data and output of results if the design is to be of any use. In student digital designs, these input/output capabilities, though essential, often overshadow the core of the design in the mind of the student designer so that s/he spends more time implementing the interface than addressing the intended focus of the system. The result is a system with a glamorous interface but compromised or limited capabilities to solve the overall problem. Described in this paper is a microcontroller-based instrument built into an old telephone handset that provides keypad input and multi-digit display output, which is easy to incorporate into typical digital designs. The keypad in the telephone handset is used as the input device, and a raster generated on a standard oscilloscope is used to produce a display showing a multiple-digit output. This device has been used as a standard interface for many different digital systems designed by students in the second quarter digital circuit design class at the University of Minnesota Duluth. Designs such as multipliers and other arithmetic circuits, stacks, queues, and other data structure implementations, and standard circuits meant to teach digital circuit capabilities have used this instrument to provide user interface to the systems, so that students can concentrate on the specific task involved with their system designs and just use the available input and output tools provided here to get data into and out of their systems. This approach has resulted in improved student ability to master digital system design without undue focus on the user interface. Presented here is the design of this instrument, and the techniques used to incorporate it into various digital system designs. Examples of laboratory exercises that use this instrument as input and output are included.