E15A Laboratory 1

Combinational Logic with Discrete Gates


In this lab you will be building some simple circuits using logic gates.

Powering the breadboard

Connect the breadboard, to the Input/Output tester (I/O) circuit as shown. We will build circuits on the breadboard, and use the I/O circuit to generate and display binary values.


The outputs B, C, D represent a 3 bit binary number and should be counting up from 0 to 5 in a pattern:

Decimal Binary
0 0 0 0
1 0 0 1
2 0 1 0
3 0 1 1
4 1 0 0
5 1 0 1

If the board is not counting from 0 to 5


If the LED's are not changing do the following:


If the count is not going from 0 to 5 (decimal):


The breadboard now has power, and is generating a test sequence, and we can build a circuit on it.

Building a simple circuit

The circuit we wish to build is shown below. There are two inputs and one output.


In other words, W is the result of C NANDed with the inverse of D.


To build this circuit we need a 2 input NAND gate which exists on an integrated circuit (IC) called the 7400. It's pinout is shown below next to a photograph of an IC.


Things to note:


To connect our circuit we ill take the output labeled ~D (not D) to pin 1, the output labelled C to pin 2 and the input labelled W to pin 3.


Note that:


Connect the circuit as shown. The output should be high except when C is high and D is low, as shown in the truth table below.

C D ~D   W
0 0 1 1
0 1 0 1
1 0 1 0
1 1 0 1



TTL Pinouts (from:http://www.tayloredge.com/reference/Packages/pinouts/). You should only need NAND gates and invertors (7400, 7404, 7410, 7420).


7400 2 input NAND

(1 input NAND)

7410 3 input NAND

7420 4 input NAND


Task 1: Cylon eye (https://www.youtube.com/watch?v=faukADr0_6g)

Your task is to make the outputs WXYZ display a pattern where one LED is lit at a time as it goes back and forth (see diagram below) as the outputs B, C, D go from 0dec (000bin) to 5dec (101bin) as shown below

B C D   W X Y Z
0 0 0   0 0 0 1
0 0 1   0 0 1 0
0 1 0   0 1 0 0
0 1 1   1 0 0 0
1 0 0   0 1 0 0
1 0 1   0 0 1 0

As the number counts repeatedly from 000bin to 101bin a single lit LED will move back and forth.

For your report include:


Task 2: Five eyes.

Design a system that accomplishes the same task but with 5 LEDs (labelled V to Z). Show all required work. You don't need to actually build the system


Task 3: Six Eyes

Repeat task 2 for six eyes (labelled U-Z)


Task 4:

Demonstrate that a circuit implementing sum of products (ands followed by ORs) can be replace by all NANDs by creating the truth table for

and for


To Turn in:

Each part of each task should be well labeled and in order. Each group should turn in one report on moodle. The report need not include a lot of prose - just make sure to clearly

Repeat steps for task 2

Include truth tables for X1 and X2.


Please contact me if you find any errors or other problems (e.g., something is unclearly stated) in this web page