Lab 2: Seven-segment displays

Now that we’re familiar with the Digital software simulator and combinational logic circuit design techniques (e.g., truth tables, sum of product (SOP) expressions, and SOP simplification using Karnaugh maps), it’s time to take things to the next level! In this lab, you’re going to be wiring up a 7-segment LED Display!

Pull the new starter code!

The starter code for each subsequent lab will be added directly into the same course repository. To update your individual repo, navigate to your workspace on the GitHub website and you should see a “Sync Fork” button. Click this and then “Update Branch.” Now if you run ``git pull’’ in your terminal, you will have all the materials you need.

IF YOU SEE AN OPEN PULL REQUEST BUTTON when you attempt to sync your workspace, please follow the below steps. If you have any trouble, come see the TAs in office hours and we will walk you through it!

1. Check for an existing SSH key

• In your terminal run:

  ls ~/.ssh

• If you see a public key file (for example id_rsa.pub or id_ed25519.pub), you already have an SSH key. You can print it with:

  cat ~/.ssh/id_rsa.pub

• If you have a key, skip to step 2 (Add the key to GitHub).

2. Create an SSH key if you do not have one already

• In your terminal run:

  ssh-keygen -t rsa -b 4096

• Press Enter to accept the default file location when prompted.

• Enter a passphrase you will remember.

• Print the public key:

  cat ~/.ssh/id_rsa.pub

• Copy the output to add to GitHub (see step 3 below).

3. Add the key to GitHub

• Copy the output of cat ~/.ssh/id_rsa.pub.
• In GitHub: Settings → SSH and GPG keys → New SSH key.
• Paste the key and give it a name like “laptop”. Save.

4. Add the starter repo as a remote

• In your local course repo run:

  git remote add starter git@github.com:comp311-fa25/comp311-fa25-comp311-fall-2025-workspace-311-fa25-starter.git

• Verify remotes:

  git remote -v

  You should see both origin and starter.

5. Sync your fork with the starter repo

• Pull updates from the starter remote using rebase:

  git pull starter main --rebase

• Repeat step 4 every time we push a new lab directory to the starter repo.

• The first time you make changes and try to push to your workspace, you may need to run git push origin main --force.

If anything fails (SSH permission errors, etc.), see a TA in office hours for hands‑on help.

Seven-segment displays

Seven-segment displays are widely used in digital clocks, electronic meters, basic calculators, and other electronic devices that display numerical information. They get their name because there are seven different lights that turn on or off depending on what number or letter is being displayed. The image below shows how a 7-segment display can be used to represent the numbers 0-9.

The display we are working with in this lab can display the digits 0-9 and the letters A-F. To control the value being shown, the display takes as an input a 4-bit binary number. The hexadecimal value of this 4-bit binary input is the character that will be displayed. For example, if the input is 0b1010, the letter A will be displayed. If the input is 0b0101, the number 5 will be displayed.

The 4 bits of the input are denoted as A, B, C, and D. For example, if the input is 0b1010, then A = 1, B = 0, C = 1, D = 0.

The name of each segment is shown below (F_a, F_b, F_c, F_d, F_e, F_f, F_g). You will create separate circuits to control each of the segments. If a segment should be on, the output of the driving circuit should be 1. If a segment should be off, the output of the driving circuit should be 0. For example, if the input to the display is 0b0000, we want to display the character 0, so F_a, F_b, F_c, F_d, F_e, and F_f would all be 1 and F_g would be 0.

Task 1

To construct the circuit that controls the 7-segment display, you will need to fill out the provided truth table. The first row and first column of the outputs in the truth table have been filled out for you.

Using the given truth-table.csv file in the repo, fill in the rest of the truth table. Determine for each number or letter which of the 7 LED’s will be on (1) or off (0). When you finish the truth table, commit your changes and submit to Gradescope to see if it is correct. If you have an incorrect truth table, your circuits in the next part will not be correct!

Task 2

Now that we’ve constructed the truth table, it’s time to get ready to build the circuit! Before we start diagramming on Digital, we need to figure out how we’re going to wire up the 7-segment display.

Step 1

Using the completed truth table, create simplified Boolean expressions for each of the output segments F_a - F_g. We recommend using K-maps. When you are finished, you should have 7 Boolean equations (one for each segment in the display).

Step 2

You will implement your 7 circuits in Lab02.dig. In this file, you are provided with 4 input pins labeled A, B, C, and D. You are also provided with 7 output pins labeled F_a, F_b, F_c, F_d, F_e, F_f, F_g. You may move these pins around, but DO NOT CREATE NEW PINS.

Output

• The output of each subcircuit should be connected to a tunnel and an output pin as shown below. The tunnel will connect the circuit to the 7-segment display. The output pin is used for the autograder.

The image below shows where to connect each of your circuits to the display. Note that the bottom right input on the display must connect to ground.

Components

• The 7-segment LED display can be found under Components > IO > Displays > Seven-Segment Display. DO NOT use the Seven-Segment Hex Display.
• The ground element can be found under Components > Wires > Ground.

Tips

• We STRONGLY recommend that you use tunnels to simplify your design.
• Make sure that when crossing wires, they don’t accidentally connect. You can tell if wires have connected if a blue dot appears in Digital. You may sometimes want to connect wires, though - just make sure that when it happens, you’re doing it on purpose.

Submit your assignment

Assignments are submitted through Gradescope.

1. Commit and push your changes to your course workspace. (The only file you should have changed is Lab02.dig).
2. Go to the COMP 311 course in Gradescope and click on the assignment called Lab 2.
3. Click on the option to Submit Assignment and choose GitHub as the submission method. You may be prompted to sign in to your GitHub account to grant access to Gradescope. When this occurs, grant access to the Comp311 organization.
4. Select your 311 workspace repository and the main branch.
5. Your assignment should be autograded within a few seconds and you will receive feedback.
6. If you receive all the points, then you have completed this lab assignment! Otherwise, you are free to keep pushing commits to your GitHub repository and submit for regrading up until the deadline of the lab.