Date of Birth
In this project, we used out date of birth (in mm/dd/yy) format to create a circuit that would display it on a common cathode seven segment display, with 220 ohm resistors used. We had to create a truth table, k-map the expressions to get the simplified one, use mulitsim to create the circuit digitally and finally breadboard it. This project combined many topics that have been covered in class into one project.
Truth Table
This truth table displays the various combinations of X, Y, and Z that are needed to display the date 10/12/98. These combinations will later be used to create the circuit itself.
The purpose of the columns that are labeled a - g is because on a seven segment display there are seven LEDs that are lit in different combinations in order to display different numbers and letters. Each horizontal row shows which LED will need to be lit in order to display the number that is written in the column that is has no label. The X's on the chart are "don't cares" which means that it can be either a one or a zero, but it won't affect the outcome if it is one or the other.
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Karnaugh Maps
Each chart shown is a K-map that is used to simplify the minterms that are produced by the truth table. In the truth table there were rows a-g which each represented a different LED, so in order to properly create the circuit, each LED must have its own expression, hence the seven different tables. Each table is labeled based on the three switches that will be used, which are X, Y and Z. Using the truth table, the K-map charts are filled in by using vertical groups of two. There were four groups that could be made so the third and fourth have to be switched when being put in the K-mapping chart for it to work properly. Then the charts 1's in the chart are grouped in groups of one, two, four, or eight. After the groups are made, you take look at the letters that are labeled on the side an the letters that are the same throughout the group are what create the minterm. The minterms that were created are in sum of products form. I chose to do K-mapping instead of Boolean Algebra because it is easier and less time consuming.
MultiSim Implementation
This circuit shows the different gates that are required for the seven segment display to work properly. The various combinations of gates are based of of the minterm expressions that are pictured above, which were produced by K-mapping. There is a circuit for each minterm, and different combinations of an, or, inverter, and nor gates were used.
This circuit does use a bus, which is the vertical, darker red line in the center of the circuit. The bus is used so that the six variables (x, not x, y, not y, and z, not z) can be used to create many different circuits without having to add extra components. In this circuit, three inverter (74LS04) gates were used, three or (74LS32) gates were used, two and (74LS08) gates were used and two nor (74LS02) gates were used. I used the nor gates for my notY+notZ expression because I thought that it would be the most simple minterm to use them in. I did not use nor gates for this part because there would've been three gates required to create that circuit and only two when using the nor gates.Nand and nor gates are used because they are universal, and all three types of the other chips (74LS04, 74LS08 and 74LS32) can be created using just one type of gate. Using the nor gate instead of the or gate caused more gates to be used, but the same amount of chips. The seven segment display is connected to the ground because it is a common cathode display. If it were a common anode display then it would be connected to power. Because the display used is connected to ground, in order for one of the LEDs to light up it has to be connected to power. If it were connected to ground while using a common cathode seven segment display, then that particular segment would not light up.
Bill of Materials
The bill of materials shows what was used when I actually bread boarded the circuit. I put approximately 40 wires because I am unsure of the actual number but I know it was close to that.
Bread boarding
The bread boarding process is becoming much easier as we do it more. I was able to bread board this circuit almost perfectly the first time, my only issue was that the seven segment display was not grounded so I had to go back and fix that. Using the physical NOR gates for the first time was a learning curve because the gates within the chip are backwards from all the other chips that we have used so that took a little bit to get used to. Other than those two issues, this was relatively easy to bread board.
Conclusion
This project helped me to learn K-mapping, and helped to better my understanding of bread boarding, truth tables and multisim. If I could change something that I did in this project, I would breadboard so that everything is more spread out because the way that I did it caused it to be very bunched up and confusing to tell where the wires were going, what was done, where errors were, etc. I still struggle with k-mapping, more particularly on big k-maps where there is more room for error. The k-maps that were completed in this project I found to be easy because they were small and the groups were easy to visualize. Over all, I think that this project was relatively easy, but still was a good combination of skills that we have learned in class, and still helped me to better those skills.