Page 149 - ARM Based Microcontroller Projects Using MBED

CHAPTER
8

Intermediate Level Projects

8.1 OVERVIEW

In this chapter, we shall be developing more complex projects using the Nucleo-F411RE
development board and the Mbed Integrated Development Environment. The projects in this
chapter will be described with the same subheadings as in the previous chapter.

8.2 PROJECT 1—TWO-DIGIT MULTIPLEXED 7-SEGMENT LED

8.2.1 Description

A single digit 7-segment LED can only display numbers between 0 and 9. In applications
where it is required to display higher numbers, we can multiplex two 7-segment LEDs to dis-
play numbers between 0 and 99. In this project, we shall be designing a two-digit display to
display the number 25 as an example.

8.2.2 Aim
The aim of this project is to show how two 7-segment LEDs can be multiplexed to display
numbers between 0 and 99.

8.2.3 Block Diagram

The block diagram of the project is shown in Fig. 8.1. Notice that in a multiplexed display,
the same data are sent to both display segments at the same time, but each digit is enabled
separately. Thus, for example, to display number 25, we first send 2 to both digit segments
and enable the digit at the left-hand side (MSD, most significant digit) for several millisec-
onds. Then, number 5 is sent again to both digit segments but this time the digit at the
right-hand side (LSD, least significant digit) is enabled for several milliseconds. When this
process is repeated, the human eye cannot differentiate that the digits are not ON all the time.
This way we can multiplex several digits easily.

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