PROJECT 05 – HALF ADDER CIRCUIT

OVERVIEW

In this circuit, you will create a half adder circuit. Essentially, a half-adder is a circuit that adds two single bits (A and B) and gives off a two bit answer (00, 01 or 10).

This project will force you to use multiple ICs to create your circuit.

THEORY

We want a circuit that will do the following:

0 + 0 = 00

0 + 1 = 01

1 + 0 = 01

1 + 1 = 10

To do this, we need to consider each output bit separately one from another. Instead of calling them Q1 and Q2, we will call them C and S to represent Carry and Sum.

This gives us the following truth table:

A B C S

0 0 0 0

0 1 0 1

1 0 0 1

1 1 1 0

But it might be easier to look at this as two separate truth tables for each output.

a) The truth table for S:

A B S

0 0 0

0 1 1

1 0 1

1 1 0

The above truth table is that of the XOR gate.

b) The truth table for C:

A B C

0 0 0

0 1 0

1 0 0

1 1 1

The above truth table is that of the AND gate.

Therefore, a half adder is created using an XOR gate and an AND gate. Below is the logic diagram and a block diagram for a half adder.

TASK

Using a 7408 TTL IC (AND gates) and a 7486 TTL IC (XOR gates), you will create your own half adder. You will need to use 4 LEDs to show the value of the 2 inputs and the 2 outputs.

You are expected to place the LEDs in such a way that the LEDs are in order.