A quick course in Binary

seven-segment led displays

LEDs are fun, but there are limits to the kinds of data that can be displayed with individual lights. In this section we’ll begin working with numeric digits in the form of seven-segment LED displays, as shown in Figure 6-9.

Figure 6-9: Seven-segment display modules
These displays are perfect for displaying numbers, and that’s why you’ll find them used in digital alarm clocks, speedometers, and other numeric displays. Each module in a seven-segment LED display consists of eight LEDs. The modules are also available in different colors. To reduce the number of pins used by the display, all of the anodes or cathodes of the LEDs are connected together and are called common-anode or commoncathode, respectively. Our projects will use common-cathode modules.
The display’s LEDs are labeled A to G and DP (for the decimal point). There is an anode pin for each LED segment, and the cathodes are connected to one common cathode pin. The layout of seven-segment LED displays is always described as shown in Figure 6-10, with LED segment A at the top, B to its right, and so on. So, for example, if you wanted to display the number 7, then you would apply current to segments A, B, and C.
The pins on each LED display module can vary, depending on the manufacturer, but they always follow the basic pattern shown in Figure 6-10. When you use one of these modules, always get the data sheet for the module from the retailer to help save you time determining which pins are which.
We’ll use the schematic symbol shown in Figure 6-11 for our sevensegment LED display modules.

Figure 6-10: LED map for a typical seven-segment display module

Figure 6-11: Schematic symbol for a seven-segment display module