Hello everyone and welcome to our blog
The first week:
On Friday we read some research about hamming
code from materials, lectures, videos, books and web pages and we look at some
pictures, schematics and circuit diagrams. In addition, we read about the
history and the advantages and the disadvantages.
Important information that we learn:
- Richard Hamming is the person who invent hamming code in 1950.
- The Hamming code detect and correct errors.
- The codes are in binary.
- In our case the Hamming code has 7 digits 4 of them are the information bits and the other 3 are parity bits.
- To get parity 1, 2 and 3 we use (B1+B2+B4), (B1+B3+B4) and (B2+B3+B4) respectively and when we get an even number it will equal 0 and when we get odd number it is equal to 1.
- In the hamming code called (7, 4) because it can encode 4 data bits into a 7 bits word.
- From this information a logic table was created which then led to the implement of K maps. This proceeded to the minimised expressions that was then used to create an initial design with logic gates.
The second week:
I downloaded LTspice and Pspice but
it was difficult to simulate our project design because there was
issues locating the required logic gates within the libraries. I then searched
on the Internet which led me to a program called Logisim which is simpler
because it contains a large number of logic gates and also various switches.
After that my partner gave me the design with
a truth table illustrating the parity for each 4 bit data
word.
The truth table illustrating the
parity for each 4 bit data word.
The decoder circuit design on paper.
The decoder circuit that is created by
using Logisim simulator.
We built the initial design and
tested it. This part of the circuit produces
the required parity code for each data word, that
circuit will be expanded upon to implement the error correction.
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The third week:
I read some research about three types of error
detection methods and I notice that:
The first type of error detection is Vertical
Redundancy Check (VRC) which is also called Parity Check. This kind of error
detection is used on 8-bit character. Moreover, it can be possibly used to
detect bits by organised channels. It also can be used for short massages and
large hamming codes. In addition, it can detect the odd errors of the data
block. On the other hand, It works with an even number only, which, make this
error check type unreliable.
The second type of error check is Longitudinal
Redundancy Check (LRC) that depends on a parity bit that is applied and on each
signal data stream blocks. In this method of detection, a table is used to
organise data by making parity for each column. Furthermore, it can detect
errors on each column. According to F, John this type is not effective enough
comparing with Cyclic Redundancy Check (CRC).
The third part of detection method is Cyclic
Redundancy Check (CRC) is one of the most effective error detection type.
Because of that it can be made by a small amount of hardware and it can
possibly shift registers. Additionally, this method can detect the transmitted
errors on a communications link. It might be generated by a shift register
feedback software.
My partner Adam designed the hamming
code circuit which he tested against the logic tables to ensure correct
operation. The image below is said design.
The hamming code circuit
The red box covers four inputs on the left for
the data word, the first set of lights and logic gates always ensure correct
parity and by extension correct message is sent. The blue box has the next set
of switches which are for the error that the logic will then correct and
display in the furthest right set of lights (the yellow box).The green
box illustrates the required message the user will receive.
Additionally, my partner designed and built the
parity checker circuit. He firstly used K-maps but it was useless
because he did not find any matches so he used the Boolean algebra to
get the smallest menterm. Subsequently, he build and test the circuit.
Boolean Algebra equation
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The fourth week:
We have done the Sustainable Development and
Ethics - Assignment.
I find out more about CRC. I watched a video on
YouTube illustrates the method of doing CRC. We have two things that we need to
work out to detect and correct the error which are word (data that is
transmitted from sender to the receiver) and divisor that is given. Firstly, we
look at how many number on divisor then we subtract 1 number from these numbers
and we add zeros to the word that is equal to the number of divisor number
after the subtraction. For example if the word equal 1101101 and the divisor
equal 10101 we add 4 zeros to the divisor so it become 11011010000. After that
we use the long division but with different rules. If the number start with 1
the answer is 1. Otherwise, the answer is 0 and we use Xor during the devotion
As shown on the picture below.
Subsequently, the number that appears on
reminder is the error and when we replace this number with the last 4 number on
the word we will get 0 reminder.
As shown on this picture the reminder is 0
after changing the last 4 bits of the word.
Look at this link for more clear description: https://www.youtube.com/watch?v=ZJH0KT6c0B0
My partner Adam researched into CRC as well.
He then designed a CRC circuit from logic that
he then built on the Logisim simulator. The circuit contains a sender part that
generates a three digit code via the use of XOR long division, this code is
then checked against the received code and if the final result is all zeros
then the message is errorless.
The correction circuit is found to be very
complex and out of scope due time constraints.
We start doing the poster.
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The fifth week:
In this week I almost finished the initial
design of the poster and the blog which I then sent to Prof. Hall to check,
asking him to give feedback about.
My partner has being worked hard on building
the circuits to finish them as soon as possible thank you very
much Adam.
As a group we went over the poster design to
implement changes as suggested by our academic adviser.
On Monday and Tuesday;
We did some changes on the poster and the blog depending on what the Prof. Hall mentioned on the feedback.
Additionally, Adam designed and build the CRC circuit.
On Monday and Tuesday;
We did some changes on the poster and the blog depending on what the Prof. Hall mentioned on the feedback.
Additionally, Adam designed and build the CRC circuit.
Initial CRC circuit simulation
Final CRC circuit
Implemented circuit 1
Implemented circuit 2
