Using LEDs, LCDs and GLCDs in Microcontroller Projects

5.8 7-Segment LEDs

7-segment displays were the earliest LED type electronic displays used to display numbers. These devices are commonly used in digital clocks and watches, electronic meters, electronic counting devices, and other equipment for displaying numeric only data.

A 7-segment LED consists of 7 light emitting elements arranged in a rectangular enclosure, and by turning the appropriate segments ON and OFF we can obtain the numbers 0 to 9. Figure 5.9 shows a typical 1-digit 7-segment display. Optionally, a decimal point is available to display fractional non-integer numbers. The segments of the displays are referred to by letters ‘a’ to ‘g’.

Figure 5.9 Typical 7-segment display

7-segment displays are available in two configurations: common anode and common cathode. As shown in Figure 5.10, in a common anode connection, the anode pins of all the segments are connected together and this pin is usually connected to the power supply. Individual segments are turned ON by grounding the required segment pin. Similarly, Figure 5.11 shows a common cathode display. Here, the cathodes of all the segments are connected together and this pin is usually connected to ground. Individual segments are turned ON by applying voltage to the required segment pin.

Figure 5.10 Common anode 7-segment LED

Figure 5.11 Common cathode 7-segment LED

5.8.1 Displaying Numbers

Figure 5.12 shows the ...