ELECTROCARIAN

  6.1 Introduction One common requirement for many different digital devices is a visual numeric display. Individual LEDs can of course display the binary states of a set of latches or flip-flops. However, we're far more used to thinking and dealing with decimal numbers. To this end, we want a display of some kind that can clearly represent decimal numbers without any requirement of translating binary to decimal or any other format. One possibility is a matrix of 28 LEDs in a 7×4 array.                       We can then light up selected LEDs in the pattern required for whatever character we want. Indeed, an expanded version of this is used in many ways, for fancy displays. However, if all we want to display is numbers, this becomes a bit expensive. A much better way is to arrange the minimum possible number of LEDs in such a way as to represent only numbers in a simple  fashion. This requires just seven LEDs (plus an eighth one for the decimal point, if that is needed). A com