Malaysian Institute of Aviation Technology
TOPIC 2:
LOGIC CIRCUITS
Prepared By : Roslam Ideris 1
Malaysian Institute of Aviation Technology
LEARNING OUTCOME
1. Identification of common logic gate symbol, tables, equivalent circuits
and Boolean expression
2. Introduction to :
• Application used for aircraft systems •
Interpretation of schematic diagrams
Prepared By : Roslam Ideris 2
Malaysian Institute of Aviation Technology
Boolean Constants and Variables
• Allowed 2 binary variables only : 1 & 0
• Represent voltages or logic level i.e. not actual
number
•May represent (in circuit) : ON,CLOSED (logic 1)
and OFF,OPEN (logic 0)
• Only 3 operation in Boolean algebra
1. Logical addition (+)
2. Logical multiplication (•)
3. Logical complementation ( ¯ )
Prepared By : Roslam Ideris 3
Malaysian Institute of Aviation Technology
AND GATE
• Logic symbol :
Input : A and B
Output : X
Prepared By : Roslam Ideris 4
Malaysian Institute of Aviation Technology
AND GATE
• Simplified equivalent AND gate circuits
• Boolean expression:
A•B=X
Prepared By : Roslam Ideris 5
Malaysian Institute of Aviation Technology
OR GATE
• Logic symbol
• Truth table
Prepared By : Roslam Ideris 6
Malaysian Institute of Aviation Technology
OR GATE
• Simplified equivalent OR gate circuits
• Boolean expression:
A+B=X
Prepared By : Roslam Ideris 7
Malaysian Institute of Aviation Technology
NOT GATE
• Also know as inverter • Logic symbol
• Truth table
Prepared By : Roslam Ideris 8
Malaysian Institute of Aviation Technology
NOT GATE
• Simplified equivalent NOT gate circuits
• Boolean expression:
Ā=X
Prepared By : Roslam Ideris 9
Malaysian Institute of Aviation Technology
NAND GATE
• Logic symbol
• Truth table
Prepared By : Roslam Ideris 10
Malaysian Institute of Aviation Technology
NAND GATE
• Simplified equivalent NAND gate circuits
• Boolean expression:
AB = X
Prepared By : Roslam Ideris 11
Malaysian Institute of Aviation Technology
NOR GATE
• Logic symbol
•Truth table
Prepared By : Roslam Ideris 12
Malaysian Institute of Aviation Technology
NOR GATE
• Simplified equivalent NOR gate circuits
• Boolean expression:
A+B = X
Prepared By : Roslam Ideris 13
Malaysian Institute of Aviation Technology
BOOLEAN TEOREMS
• Single variable theorems
Prepared By : Roslam Ideris 14
Malaysian Institute of Aviation Technology
BOOLEAN THEOREMS
• Multivariable theorems
Prepared By : Roslam Ideris 15
De Morgans Rules
Prepared By : Roslam Ideris 16
Malaysian Institute of Aviation Technology
Exclusive OR (XOR)GATE
• Logic symbol
• Truth table
Prepared By : Roslam Ideris 17
Malaysian Institute of Aviation Technology
XOR GATE
• Simplified equivalent XOR gate circuits
• Boolean expression:
ĀB+AB = X
Prepared By : Roslam Ideris 18
Malaysian Institute of Aviation Technology
XNOR GATE
• Logic symbol
• Truth table
Prepared By : Roslam Ideris 19
Malaysian Institute of Aviation Technology
XNOR GATE
• Simplified equivalent XNOR gate circuits
• Boolean expression:
AB+ĀB = X
Prepared By : Roslam Ideris 20
APPLICATION
Prepared By : Roslam Ideris 21
Malaysian Institute of Aviation Technology
APPLICATION
• Consist of 2 OR gates and an AND gate, with
logic states received from 7 parameters
• When either throttle lever is pushed forward, the
switch at that position is made (advance) and
there is a logic state 1 to OR gate1.
• 5 other parameters are sensed and logic states
sent to OR gate2.
Prepared By : Roslam Ideris 22
Malaysian Institute of Aviation Technology
APPLICATION
• If all the other parameters are in the take-off position, i.e.
1. Slats not fully extended
2. Flaps in take-off position i.e. less than 25°
3. Spoiler handle in retract position
4. Horizontal stabilizer in the green band (correct
angle of incidence for take-off).Then the inputs
to OR gate2 are all logic 0 and it’s output to the
AND gate is logicPrepared
state 0
By : Roslam Ideris 23
Malaysian Institute of Aviation Technology
APPLICATION
• The aircraft on ground (weight switch) gives
another logic 1 to the AND gate, which has at
this time 2 logic 1’s and a logic 0
• If either of 4 inputs go out of take-off position
eg flaps >25°,then the flap input signal to logic
gate2 is logic 1 which makes the input to the
AND gate logic 1
• The AND gate now has 3 logic 1’s which now
gives an output to warning circuits (CONFIG
light and aural warning)
Prepared By : Roslam Ideris 24
