Environmental Monitoring with Arduino

Chapter 3. New Component: 4Char Display

In the next project, we’re going to display our data on a serially driven four-character LED display (see Figure 3-1). This is a wonderfully versatile little tool that incorporates four seven-segment LED displays that show, natch, four characters of data at a time (as well as a colon and decimal points).

The four-character display can show all of the Arabic numerals from 0 to 9, as well as 20 of the 26 letters used in English, some of them in both upper and lower cases. To see how they look, check out Figure 3-2. (There are some pseudoconventions for displaying the letters k, m, v, w, and x, but if you use them, most people won’t recognize them as letters—some of them look just like random illuminated segments—and will think there’s something screwy with the display).

“Serially driven” is the distinction that makes this display so useful. With a standard seven-segment display, each segment of the display needs its own dedicated data line from Arduino to control it. Using four characters in this type of display architecture (along with the associated decimal points and colon) would require 34 dedicated data lines, more than the standard Arduino even has. (Granted, there are tricks to get around this, but even then, the display would still need a lot of lines.)

So the people at SparkFun, who make this product, added a microcontroller to the back of the display. This microcontroller can take serial data sent from a single Arduino pin and interpret ...