COMBINATIONAL LOGICCOMBINATIONAL LOGICCircuit DesignCircuit Design

Steps

• Create the truth table

• Extract the Boolean Expression from the truth table or create a K-Map

• Simplify the expression

• Draw the schematic

• Build the circuit

Design a safety alarm system for a car that alerts the driver when the seatbelts have not been fastened, or when the door is ajar while the key is in the ignition.

A=Key B=Door C=Seatbelt

A B C X0 0 00 0 10 1 00 1 11 0 01 0 11 1 01 1 1

00000111 ABC

ABCABC

Boolean Expression Is:

ABC + ABC + ABC=X

Logic Problem

K-Map

XABCCABCBA XCCABCBA )(

XABCBA

Dist.

Th. 4

XABCBA 1 Th. 6

XBCBA )( Dist.XBCA )( Th. 11

XABAC Dist.

Boolean Simplification

ABC

0 0

0 0

0 1

1 1

0 1

00

01

11

10

XACAB

Create Expression & Simplify

Create Circuit Schematic

X

NAND Only Solution

MultiSIM Demo

Warning light

B=DoorA=Key C=Seatbelt

AB+AC

0V0V0V