For this project we had to build a circuit that had a seven segment display that was able to say our date of birth. We needed a common cathode display, that used at least one NAND circuit and one NOR circuit. We had to use Karnaugh mapping to simplify.
Truth Table and Karnaugh Mapping
The picture above is my truth table and K-mapping. I used the K-mapping to simplify the expression from my truth table. In the truth table we had to right out our birth date, mine is 03/05/99, and write out how the seven segment display will show it. The letters A-G are the segments on the display. The X's on the bottom mean that they aren't needed. They could be 1 or 0. K-mapping is a way of simplifying the truth table. The K-mapping were used for each segment. The numbers were from the table and put in vertically for each segment. Each table were labeled the same, X and Y on the side and Z on top. In K-mapping you try to group the 1's in groups of 2,4, or 8. The segments A,C,D didn't have an expression because all the numbers in the K-mapping were 1. Segments B,F,G were SOP. Segment E was a POS. I used K-mapping instead of Boolean algebra because it is much simpler. We needed an expression for each segment.
This is the circuit for my project and it was built in MultiSim. It has 3 switches that are used to change the display. I used 16 gates in my circuit.
For this circuit I had to use a bus because there were 7 circuit I had to make. I had to use 3 inverting gates, 3 NAND gates, 6 AND gates, 2 OR gates, and 2 NOR gates. I used 5 chips in my project even though my MultiSim circuit need 6, that was because i didn't simply all the way. I could have used NAND or NOR gates in any of the circuits. We use NAND and NOR gates because they can be used to make any other circuit. If I used only NAND gates, I would use the same amount of chips. If I used NOR gates, I would use one less chip. Most of the expressions are SOP, so NOR gates would help reduce the number gates. Less chips means less money spent of building the product. The seven segments have seven inputs that represent each segment. Each input have their own circuit. A common cathode is grounded and a common anode is powered. We are using a common cathode because that is what is on the board. The resistors are used to reduce current to the display.
Bill of Materials
This is a list of materials needed for this project. We didn't need any resistors because they were built into the board.
Picture 1: Empty Breadboard. Picture 2: Breadboard with IC chips. Picture 3: Wiring during the project. Picture 4: Final Product.
This project took a lot of wires and it was hard keeping track of the wires. I messed up several connections and forgot to but one gate connection the messed up my B segment. I learned how to power the display and how to wire a seven segment display. I had to look at every circuit to make sure all the connections were right. The NOR chip was built backwards compared to the other chips. The inverting chip had one input for each gate. Each was powered by the top left pin and grounded by the bottom right pin.
We started our project by making a truth table in our engineering notebooks. After the truth table we had to simplify the expressions for each segment. I used K-mapping to simplify. I had 3 segments that just needed to be powered with out chips. When we had all our expressions we started bread boarding. I needed to use one of each chip (00,02,04,08,32).
What did you learn from this project?
I learned how to wire a circuit that would display a number on a seven segment display.
What would you do differently next time?
Actually follow my Multisim design and not forget a circuit. Also i could use one color wire for a circuit.
What questions do you still have about the concepts addressed in the project?
How much more simplified could I have made my circuit?
Why is K-mapping useful?
It is much faster than Boolean Algebra and you can find the expression for easily for each segment faster.