EXPERIMENT 5: INTRODUCTION TO 7 SEGMENT DISPLAY
You are welcome to another episode of my Embedded systems tutorials for beginners. You can get previous tutorials from this link…
https://www.nairaland.com/2255112/embedded-systems-tutorial-beginners-experiment and if you are new to this series of tutorial you can start from the beginning… https://www.nairaland.com/2175195/embedded-systems-future-electronics-computer


Tools needed:
Software: Proteus 8 to simulate the software on virtual hardware, CCS compiler version 4.0 and above to write and compile programs, pickit2 IDE to burn your compiled code into your MCU
Hardware: Bread board, common cathode 7 segment display, pic16f88, 7 segment display, pickit2 programmer, USB cable and power bank or USB charger to create 5v supply. All the hardware components can be gotten from a reputable Electronics Component supplying company http://hub360.com.ng/shop-2/hub360-pic-starter-kit/

Overview:
The fifth experiment in this series of tutorial is to learn about seven segment displays which are widely used as output display in embedded systems applications.
A seven-segment display (SSD), is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays. Dot matrix display are used for alphanumeric and graphical characters Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information. Comparing the dat matrix display and 7 segment display below we will see that to display figure “1” in dot matrix requires 11 dots while in 7 segment display requires 2 segments.

FULL ARTICLE WHICH CONTAINS DIAGRAMS IMAGES AND TABLE IS ATTACHED TO THIS POST


With the 7 segment displays you can display any number or some alphabets that your heart desires. At first controlling a 7 segment display seems quite complex but it quickly becomes clear when you are familiar with it and you understand its working principles.
A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce simplified representations of the Arabic numerals. The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays for full alphanumerics display. For the sake of this tutorials for beginner, we are going to limit ourselves to 7 segment.
The seven segments is universally labeled and this standard is used world wide. It is labeled alphabetically clock-wisely as in the diagram below:

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TYPES OF 7 SEGMENT DISPLAY:
There are two types of LED 7-segment displays with respect to their logical operation and circuit connection: common cathode (CC) and common anode (CA). The difference between the two displays is the common cathode has all the cathodes of the 7-segment LED connected directly together and the common anode has all the anodes of the 7-segments connected together. Shown below is a common anode seven segment.


As shown above all the anode segments are connected together. When working with a CA seven segment display, power must be applied externally to the anode connection that is common to all the segments. Then by applying a ground to a particular segment connection (a-g), the appropriate segment will light up. An additional resistor must be added to the circuit to limit the amount of current flowing through each LED segment.


A common cathode seven segment is different from a common anode segment in that the cathodes of all the LEDs are connected together. For the use of this seven segment the common cathode connection must be grounded and power must be applied to appropriate segment in order to illuminate that segment.


WRITING THE PROGRAM
Using a microcontroller to control a SSD requires at least 7 pins, so PIC12f683 cannot be used because it only has 6 ports except a BCD to & segment decoder IC is going to be used with it, but that makes the circuit more complex. So we use PIC16F88 that has enough IO pins (16).
We are going to control the port altogether. We are going to be putting some values into the port which will enable the SSD to form the figure pattern that we want. Below is the table to that shows the pattern logic and the 8-bit data combination. The segments are arranged g-a because we want to connect a-g to port b0-b6 respectively and you know the least significant bit, bit0 starts from the right.

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