CS 3410 Lab 2: LED Numbers

Pairing: You are welcome to work with someone in your lab section on this lab but you must each submit your own solution to CMSX.

Due: This lab is to be completed entirely in Lab Section. If you are unable to finish for whatever reason, please go to office hours on Sunday. After you are done, submit a single file with your main 7-segment display and decoder circuits.

Step 0: Background Info

A 7-segment display is a form of electronic display that utilizes 7 LED segments to display the digits 0 through 9. You may have seen this in a standard calculator, alarm clock, et cetera.

Today, you will be implementing a decoder for displaying the input digit on the Logisim 7-Segment display.


7-Segment Display Example

Step 1: Truth Table

A truth table shows how a logic circuit output responds to various combinations of inputs. It is an important tool for constructing and testing your circuit.

Create a truth table for the 7-segment display translating how the input should translate into lit and unlit LED segments. You will only need to handle inputs from 0-9; other inputs are undefined.

Checkoff: Show your LED truth table to your TA

Step 2: Using the 7-Segment Display

Now that you have a decoder truth table, set up the main circuit which will eventually use your decoder subcircuit. Use the following images to help you with setting up the 7-segment display.


7-Segment Display Logisim File location and input information

Step 3: Using Combinational Analysis

You will find using the “analyze circuit” feature of logisim useful for this lab. In logisim, go to Project → Analyze Circuit. Use the combinatorial analysis feature and your truth table to build a circuit.


Combinational analysis information

Begin by adding the Inputs bits, followed by the Outputs for each segment of the LED. Lastly, click on the entries in the Table to fill out the truth table with the one from Step 1.

Step 4: Combine and Test

Use your new decoder to complete the main 7-segment display circuit. Test that your display works for all single digit inputs 0-9. (Inputting anything else is undefined behavior.)

Checkoff: Show your 7-segment display to your TA

Step 5: Submit

You've completed lab 2! Please make sure you have demonstrated your working 7-segment display to your TA and submitted your .circ file to CMSX.