PRACTICAL TRAINING MODULE/EXERCISE

1. DEPARTMENT: COMPUTER/ICT
2. SECTION/TRADE: COMPUTER CRAFT
3. CLASS: COMPUTER CRAFT YEAR 1
4. TOPIC: NUMBER SYSTEM (BINARY CODE DECIMAL (BCD) SEVEN SEGMENT CODE)


5. OBJECTIVE/SPECIFIC LEARNING EXPERIENCE:
     At the end of the practical Training module, the students should be able to:
   (i) Describe the BCD code
   (ii) Convert 4-bit binary code to BCD code
   (iii) Describe the seven segment display code
   (iv) Identify the two different types of seven segment Display Device
 
6. WORKING CIRCUIT/DIAGRAM/DESCRIPTION:

 This is the working circuit for the practical project. You will buy 7 switches, 7 resistors of 270 ohms, 4 x 1.5 AA battery (Medium size), buy common cathode seven segment display device. Locate the common cathode pin and connect it to the -ve pole of the battery. Locate the A to G segment of the device, by testing each pin to see which pin light each segment. Then connect the circuit as shown by the circuit diagram. Note that the pins of the seven segment you will buy in the market will not be arranged as in the diagram, for this one is just for presentation. The one you will see in the market will look like the one below. Get a circuit board and mount the device and each switch that will control each segment.

From the diagram below, there are two display. One on the left is actual device, while the one on the right is show the internal circuit arrangement of the the device. From the one on the right, you will see that the device has 10 pins. 5 pins up and 5 down. The two middle pin from up and down is the same thing, you can be sure of this if you trace the Gnd pin from up down. So, to connect the ground, you just need to connect one of it to the negative pole of the battery (which is the one down). The last pin down on the right is not needed in this project so ignore it.

Watch the Animation below to get the idea of the kind of result you will get when you test your final circuit.

TRY AND OBSERVE THE CLOSING AND THE OPENING OF THE SWITCHES AND HOW IT AFFECT WHAT IS DISPLAY BY THE DISPLAY DEVICE.

7. LIST OF MATERIALS:

    (i) Seven pieces of switches (the type like these ones shown below)

                        

        if you buy the first one, the middle pin and the pin for the side marked '1'          is connected.

       (ii) Common cathode 7-Segment Display

       (iii) Seven pieces 270 ohms resistors

       (iv) circuit board

       (v) 4 pieces (1.5) batteries

       (vi) 4 sides battery container

       (vii) connecting wires

The materials above are those needed for the project, but the one below are going to be your working tools when you resume for proper training.

8. REQUIRED TOOLS:

     (I) Project Board

     (ii) Digital Multimeter

     (iii) Small Electronic screw tool box

     (iv) connecting wires (flexible wires)

     (v) Soldering iron

     (vi) Soldering lead

     (vii) light Emitting Diode (LEAD), RED (10), Yellow (10), Green (10)

     (viii) 5 circuit boards 

  PROJECT QUESTION:  

FROM THE TOPIC SHOW CASE SO FAR ON THIS SITE

1. EXPLAIN AND DESCRIBE THE BCD CODE

2. EXPLAIN AND DESCRIBE THE SEVEN SEGMENT DISPLAY CODE

3. FINALLY FOUND OUT HOW BCD CODE AND SEVEN SEGMENT DISPLAY CODE WORK TOGETHER (YOU CAN FIND MORE INFORMATION FROM OTHER SITE FOR THIS).   

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SEVEN SEGMENT DISPLAY CODE

WHAT IS SEVEN SEGMENT DISPLAY

A seven-segment display, or seven-segment indicator, is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot matrix displays.
Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information

7 segment display is found in LED and LCD numerical displays, where any decimal digit is made up of 7 segments arranged  figure 8, with an extra LED or LCD dot that can be used as a decimal point. Each Segment of a Seven Segment Display is represented by letter A to G. The Display of any any number depends on the combination of two or more segments.THE 7-SEGMENT DISPLAY CODEThe Seven Segment Display code is form by a series of ON and OFF of the seven segment. For example, to form figure 1, segment B and C will be ON and the remaining segments will be OFF.The Table below show the  decimal digit and the corresponding seven segment code.

SEVEN SEGMENT DISPLAY CIRCUIT

The aim of this circuit is to demonstrate how the seven segment display displays the number figures from decimal number one to nine and back to zero. 

This animated GIF shows the seven segment display and a table showing the corresponding seven segment display code as indicated in the table above. Each rows shows A to G representing each segment as labeled on the display, and bit 0 or 1 to show the ON or OFF state of each segment of the display.

This second animated GIF shows an animation of seven segment circuit. The table show A TO G representing switches. When a segment for example 'A' show 1 it mean the switch is ON and when it is 0, it means the switch is OFF. The arrows indicate connecting wires. When they are red then current is flowing, but when they are blue, it means current is not flowing. 

TYPES OF SEVEN SEGMENT DISPLAY

There are two types of seven segment display based on they mode of connection.
There is common Anode and common Cathode. Anode is equivalent to +ve pole and Cathode is equivalent to -ve pole.

     

                                                                                                                                                    The diagram above reveal what is inside each segment of the display device. It is actually Light Emitting Diode called LED, the one normally found in touch lights. It has two terminal, a longer one called Anode and the shorter one called cathode. Anode is connected to the positive pole of the battery and cathode to the negative pole of the battery. When connecting each LED, it is either you connect each Anode to different switch and the cathodes to a common point direct to the negative pole called ground (Common Cathode), or connect the cathode of each LED to different switch and then to the ground, then all the Anode to a common point to the positive pole of the battery ( Common Anode).  

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BINARY CODED DECIMAL (BCD)

DEFINITION: The word BINARY CODED DECIMAL stands for Decimal number 0 - 9 in which four bits binary number 0000 to 1001 are used to represent each digit of the the decimal numeral. Or can be seen as decimal numbers coded with four bits binary numbers.

In BCD each number is defined by a binary code of 4 bits. The Code is           8 - 4 - 2 - 1, it indicate the weights of each bit 2³ – 2² – 2¹ - 2⁰  
Any number that is beyond 9 will be considered to have 2 digits and each digit will have its four bits binary equivalent. That is, for example, 12 will have its binary equivalent for 1 and 2, which is 0001 0010. 
E.g. 542 = 0101  0100  0010.
                   5       4        2

The difference between the ordinary four bit binary number and BCD is that binary number of decimal numbers greater than 9  is still four bits which ends with 1111 representing 15, while in BCD, it is 8 bits.
the table below shows the decimal,binary and BCD equivalent.



CONVERSION FROM BINARY TO BCD

When Binary numbers are added and the result is not greater than 9, the equivalent binary number is always the same with the BCD. But when it is greater than 9, the binary value will not be valid in BCD. For example, if the result is 15, that is, 1111 it has to be converted to BCD. To do so, 6 (0110) has to be added to the result.
                                         15 =        1111
                                           6 =        0110
                                                        0101
From the addition, the leftmost addition has a carry of 1, which is carried to the next place value.
The result is 0001 0101 which correspond to what we have on the table.
To prove this, the difference between any BCD and corresponding Binary is 6 (0110).

Why number 6 added ? 6 is being added to binary numbers because after 9 there are 6 additional digits to complete the 4- bits binary number of 1111. So, to reset the excess binary number back to 9 (1001) or binary that is within the BCD range 6 (0110) is added to make the counting skip the remaining six decimal values i.e from 10 to 15 which does not obey BCD to return to the BCD codes.

USES OF BCD CODE

BCD Code find usefulness when processing numerical values to be transmitted and display by digital electronic devices which uses seven segment display devices. This device is found in Calculator, Digital Watches.

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