Date of Birth

The circuit you will be building will allow you to display your date of birth on a seven segment display in the format MM-DD-YY. You will use NAND and NOR chips for the circuit. You will have three switches as your inputs and from these three inputs you can make eight different combinations, 000-111, each combination relating to a different section of your seven segment display. By the end of your circuit you will have mastered NAND, NOR, and seven segment displays.

Step 1: Materials

Materials: Breadboard, breadboard companion, assorted wire (different colors help to organize your bread boarding), needle nose pliers for dealing with small wires, logic probe for testing and trouble shooting, rpack of 270 ohms, 7400 NAND chips, 7402 NOR chips, wire strippers, 7500 seven segment display, and a circuit designing software. Also a friend to vent too about engineering problems is helpful.

Step 2: Truth Table

Your first step in the process is to set up a truth table. Start out as you normally do listing 000-111, but for your output list the number that corresponds to that combination. My birthday is 12-17-96. So my 000 combination outputted a "1", my 001 a "2", and my 010 a "-" and so on and so on. Then list out abcdefg to the right of the table, each letter corresponds to a different section on the seven segment display. Fill in 1's and 0's for abcdefg depending on if the segment is on or not. For my 000 I was supposed to display a 1. With segments b and c having 1's and the rest were 0's. Look at the picture for clarification if you are confused.

Step 3: K-mapping

After you have completed your truth table it's time to K-map it in order to find the word for each segment. You need to do a K-map for each segment. Once you have done a K-map for each segment it is time write the word down for each segment. Depending on your date of birth you may have the same word for two different segments. For example for my date of birth 12-17-96 and my d and e segments were the same.

Step 4: Circuit Design

After K-mapping and finding all the words for each segment you can start developing the circuit design. Draw each segment independently, you will add them together in a later step. I prefer to draw them in AOI first and then switch those over to NAND or NOR depending on which you use. This is up to you though and is a matter of opinion. Once you have drawn the circuit out and simplified it for each segment place it into a digital circuit designing software. Once each individual segment is in the software you can run the output of each section through an rpack and into a 7500 seven segment display to check if your circuit works correctly. If so great you are ready to start bread boarding if not trouble shoot until you can get it working. Common issues are not transferring the word into a circuit properly, or using the wrong seven segment display.

Step 5: Breadboarding

Once you have done all of that you can start to breadboard your circuit. I typically start out by laying out all my components then hooking up power and ground for them. Then I would recommend you run your switches across your board almost like a bus line so you can pull from them without using spaghetti wiring. Another thing you can do depending on your breadboard is to add on to the breadboard with another one by using the clips on the side of it. This would give you more space to work with. After wiring your board up making sure to use the rpack, you can test your circuit. If it works great job if not use the logic probe to compare to your circuit you built in the software until you find your problem. Common issues are broken wires, broken chips, or poor contact between wire and breadboard. It may be stressful but keep persevering, anyway this is what your engineering buddy is there for to vent to.