03-12-2012, 01:15 PM
DESIGN AND TESTING OF A SEVEN SEGMENT DECODER
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ABSTRACT
In this lab, a seven-segment decoder was designed and simulated on a computer
using Mentor's graphics software package. After its design was found to be
working properly, it was constructed and tested. This seven segment decoder
could display all hexadecimal characters (0-9 and A-F) on a seven segment
display. This design is widely used in electronic devices such as digital clocks,
digital calculators, and cell phones.
Introduction:
The seven-segment decoder designed and built in this lab simply uses a 4-bit
input to display the characters 1-9 and a-f on a seven-segment display. The
design was done on Mentor’s design software and simulated to make sure the
schematic derived using Karnaugh maps was correct. It was then built in lab and
tested.
Background and Theory:
Most electronic devices begin on the basic level that was started on in this lab.
That is, the designing using truth tables and Karnaugh maps. See Appendix II
for an example of a truth table, and Appendix III for the corresponding Karnaugh
maps.
Note that these are just representations in binary of what needs to be designed.
For the seven segment decoder being designed and built in this lab, the basis for
the given binary numbers is that the seven segment display in figure 1 is active
low. This means that when the input to each segment is low (zero), that segment
will light up. (For specifications of the display see Appendix II).
The display used in this lab (that in figure 1) just uses seven binary inputs that
control which of the seven different segments (a through g) will light up. The
decoder that will be designed and implemented will take
the four bit input and convert it to the proper seven binary
values that will give a display that corresponds to the four
bit input. The decoder would cause the binary input 0000 to
display a zero, 0001 would display a 1, and so on, all the
way to 1001 for a nine. After nine, the characters a through
f would then be displayed, thus using all possible
combinations of a four bit binary input at 1111 (there are
sixteen possible combinations). This decoder could really
just be thought of as a hexadecimal display.
Conclusion:
In this experiment a seven-segment display was successfully designed and
implemented using the bottom-up design technique, in which the small
components are built first, and then added to a larger component until the design
is complete. This worked quite well since each component designed could be
tested before making the top-level design, which covered all the components.
The design began with the lowest level of design, that is, the truth table. It was
arranged into the popular Karnaugh map format, allowing for reduction and
minimization. From the maps, the expressions needed for the design were
carefully derived and used for the decoder schematic. This step is crucial since
one small error could largely effect the output.
The design was simulated on the computer using Mentor’s computer software
package. By doing this, errors could be detected and taken care of before
hardware implementation. This is a very important step in designing that could
save much time and money.