Design Specification

The starting point for an electronics design is a specification, which should state clearly the system performance requirements. Our example project is called BAR1 (Figure A.1). This is used as the project folder name and the file name for the project files. The specification is as follows: When a button is pressed, the system generates an 8-bit binary count, starting at 0, on a bar graph display. The output frequency at the least significant bit is 50 Hz, giving an overall cycle time of 2.56 sec.

This specification could be elaborated by, for example, requiring a battery supply. In that case, an LCD display would be preferred for its low-power consumption over the LED display used in the prototype.

A block diagram is useful for clarifying the hardware design. The function of each main circuit block should be identified, as well as the signals in and out. In digital circuits, the polarity of the signal can be indicated (!Run=active low input) and a parallel output represented with a block arrow (x8=8 bits). The standard word processor has all the drawing tools needed to create simple block diagrams.