electronics chapter 4

8/11/2019 electronics chapter 4

1/27

LESSON 4

Analysing logic gates

Common terminology of logic gates

Logic gate : An electronic circuit with a single output and one or more inputs .

Truth table : A table that summarises all the possible input and output of a logic gate.

Boolean algebraic: A form of symbolic logic which provides a mathematicalprocedure for manipulating logical relationships in symbolic form.

Number of possibilities inputs and outputs..

N = 2n

N = number of outputs n = number of inputs

Types of logic gates

There are seven types of logic gates: (a) NOT gate (b) AND gate (c) OR gate (d) NAND gate (e) NOR gate


2/27

NOT gate

The symbol of for a NOT gate is:

The Boolean algebraic is:

The truth table is:

Input Output A X 0 1 1 0

An equivalent circuit to a NOT gate:

Input Output A X

Switch off Lights up Switch on Goes off


3/27

AND gate

The symbol of for an AND gate is:


The truth table is:

Input Output

A B X 0 0 0 0 1 0

1 0 0 1 1 1

An equivalent circuit to an AND gate:

Input Output

A B X


4/27

Switch off Switch off Goes off Switch off Switch on Goes off Switch on Switch off Goes off Switch on Switch on Lights up

OR gate

The symbol of for an OR gate is:


The truth table is:

Input Output

A B X 0 0 0 0 1 1 1 0 1 1 1 1

An equivalent circuit to an OR gate:


5/27

Input Output

A B X Switch off Switch off Goes off Switch off Switch on Lights up Switch on Switch off Lights up Switch on Switch on Lights up

NAND gate

The symbol of for an NAND gate is:


The truth table is:

Input Output

A B X 0 0 1 0 1 1

1 0 1 1 1 0

NOR gate

The symbol of for an NOR gate is:


6/27


The truth table is:

Input Output

A B X 0 0 1

0

1

0

1 0 0 1 1 0

Example 1

The figure shows a logic gate with inputs P and Q.

If the input P = 0011010 and the input S = 1100011 , what is the output X?

Solution

Example 2

The diagram shows two signals are connected to the inputs A and B of an OR gate.

Draw the output signal X.

Solution


7/27

Example 3

Work out the truth for the combination of logic gates in figure below.

Solution

Applications of Logic Gates in Control Systems

(1) Automatic Fan for cooling system

Light Detector

Temperature Detector

Fan

0 0 0 0 1 0 1 0 0 1 1 1

(2) Fire Alarm system


8/27

Smoke Detector

Heat Detector

Siren

0 0 Not activated 0 1 Activated 1 0 Activated 1 1 Activated

(3) Fire Control system

Input Output

Smokedetector

Heatdetector

Fire extinguisher

Fire Alarm

0 0 0 0 0 1 0 1 1 0 0 1

1

1

1

1

(4) Automatic Heater


9/27

Input Output

Switch Temperature detector

Lightdetector

0 0 0 1 1 0 0 0 0 0 1 0 1 0 1 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 1 1

(5) Control system for street lights

Input Output

Switch Light sensor Street light 0 0 1 0 1 0 1 0 1

1 1 1

TUTORIAL 4

1 What is the possible number of outputs of a logic gate which has five inputs?

A 10 B 16 C 25 D 32 E 64

2 The diagram shows an electric circuit.


10/27

Which of the following symbol is equivalent to the circuit above?

3 The diagram shows an electric circuit.

Which of the following logic gate is equivalent to the circuit above?

A AND gate B OR gate C NAND gate D NOR gate

4 The diagram shows a logic gate G whose truth table is a shown in the table below.


11/27

M N X

0 0 0 1 0 0 0 1 0 1 1 1

A AND gate B OR gate C NAND gate D NOR gate

5 The circuit represents a Boolean algebraic principle with output Z.

Which of the Boolean algebraic expression represents the output Z? __

A Z = X Y B Z = X Y __ _____

C Z = X Y D Z = X Y

6 Which of the following is equivalent to a NOT gate?

7 The diagram shows a circuit containing three logic gates.


12/27


A OR gate B AND gate C NOT gate D NAND gate

8 The diagram shows the combination three logic gates.

The truth table for the combination of three logic gates is as follows. Input Output

P Q R 0 0 1 1

0 1 0 1

1 1 1 0

What is the gate X?

A AND B OR C NAND D NOR

9 The diagram shows a circuit containing four NAND gates.


A OR gate B AND gate C NOR gate D NAND gate

10 A NOR gate with input signals M = 01010101 and N = 011010100 . What is the outputsignal of the logic gate.

A 01010101 B 10000010 C 01111101 D 01000000

11 The diagram shows a circuit containing three logic gates.


13/27

If the input signals P and Q are respectively 1001 and 1100 what is the output signal at X?

A 0001 B 0010 C 1010 D 1110

12 The diagram shows a logic gates circuit.

Which of the following truth table represents output R in the circuit?

A P Q R B P Q R

0 0 1 0 0 0 0 1 0 0 1 1 1 0 1 1 0 0 1 1 0 1 1 1

C P Q R D P Q R

0 0 0 0 0 0 0 1 1 0 1 1 1 0 0 1 0 1 1 1 0 1 1 0

13 The diagram shows a combination of three logic gates.


14/27

Which truth table is correct for the combination of three logic gates?

A P Q R B P Q R

0

0

1

0

0

0

1 0 1 1 0 0 0 1 1 0 1 1 1 1 1 1 1 0

C P Q R D P Q R

0 0 0 0 0 1 1 0 0 1 0 1 0 1 0 0 1 0 1 1 0 1 1 1

14 The diagram shows the combination of four logic gates.

Which of the following is the correct truth table for output X?

A X Y Q B X Y Q

0 0 0 0 0 1 0 1 1 0 1 1 1 0 1 1 0 1 1 1 0 1 1 0

C X Y Q D X Y Q

0 0 1 0 0 0 0 1 0 0 1 1 1 0 0 1 0 1 1 1 1 1 1 1

15 The diagram shows a circuit containing two logic gates.


15/27


16/27

17 The diagram shows the combination of AND gate , OR gate and NOT gate.

Which of the following is the correct truth table for output C?

A A B C B A B C

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

C A B C D A B C

0 0 0 0 0 1 0 1 1 0 1 0 1 0 0 1 0 1 1 1 1 1 1 0

18 The table shows a truth table for a combination of logic gates. P Q R 0 0 1 0 1 0 1 0 0 1 1 0

Which of the following is true to show a circuit according to the truth table above?


17/27

19 The figure shows a OR gate with input signals P and Q.

Which of the following is the output signal of the OR gate?

20 The figure shows a OR gate with input signals P and Q.

Which of the following is the output signal of the OR gate?


18/27

21 The diagram shows a logic gate circuit with input signals, K and L.

Which of the following output signals is produced by the logic gate circuit?


19/27

22 (a) The diagram shows a logic gate ,L with input signals A and B.

(i) Name the logic gate L.

.. (ii) Draw the output signal C in the graph below.

(c) Later , logic gate L is connected to logic gates M and N as shown in the diagrambelow.

(i) Complete the truth table below.

X Y Z

0 0 0 1 1 1 1 1

(ii) State the Boolean algebraic to relate X, Y and Z.

..........................................................


20/27

23 The diagram shows a circuit is used as a safety system in a house.

(a) Name logic gate R.

............................................................................. (b) Using two switches , two dry cells and a bulb draw a circuit that equivalent to logicgate S.

(c) The following truth table represents the logic gate in the figure above. A B L M 0 0

0 1 1 0 1 1

(i) Complete the truth table above.

(ii) State the Boolean algebraic to relate L, A and B.

............................................................ (ii) What happen to door and the gate when the main switch is closed?

............................................................

............................................................ (iii) Give two methods to open the door and the gate simultaneously.

............................................................

............................................................


21/27

............................................................

............................................................ 24 (a) Figure shows a circuit made up from a

combination of a few basic logic gates.

Figure (a)

(i) Based on the arrangement of the logic gates in the Figure (a) complete the truthtable below.

Input Output K L M 0 0 0 1 1 0 1 1

(ii) State a single logic gate which produced the same output as the output in (a)(i).

.. (b) Figure(b) shows a circuit diagram of a vending machine . The vending machine accepts 10 sen coins, 20 sen coins and 50 sen coins.Three light dependent resistors (LDR) , X , Y and Z are used to check the size of coins slotted inthe machine. The light sources of the slot machine where the coins are slotted are as shown inFigure (c).


22/27

Figure (b)

Figure (c)

(i) Complete the truth table in the table below.

State ofLDR

Input Output

X Y Z K L M S

Nocoin 0 10sen 0 20sen Bright Dark Dark 0 1 1 0 50sen 1

(ii) Name the gate that is probably in the black box.

25 The diagram shows a logic gate system is used in a factory to ensure the volume of paintin containers is within the predetermined range.


23/27

The operation of the system is shown in the truth table below.

Volume of the paint

Input X Input Y Output Z

less 1

1 1

in the range 1 0 0

exceed 0 0 1

(a) (i) Name the detector used.

.. (ii) Explain why input X is 0 when the volume of the paint exceed.

.. (b) (i) Using two NOT gates and an ANDgate, draw a circuit to represent the truth table above.

(ii) State the Boolean algebraic to relate X, Y and Z.

26 Ali wishes to design a security system in his

house as shown in Figure (a). When a person crosses the infrared beam at night, the infrared sensorwill send a signal to a logic gate which then lights up a spotlight. The spotlight has a 240 V alternatingcurrent (a.c.) supply and will only light up at night.


24/27


25/27


26/27

A: Up button B: Down button

The lift motor only activates when someone presses any one of the buttons.

Figure (a) shows the circuit that can be used to activate the motor.

Figure (a)

Keys:

Buttons A and B: When pressed, logic 1 Not pressed, logic 0

X Output : Motor is activated,logic 1

(a) The table is a truth table which shows the operations of the logic gates in a lift motor. Using the keys given, complete the table.

A B X

0 0 0 1 1 0 1 1

(b) Why is a relay switch needed in the circuit?

(c) The door of the lift is fitted with a light transmitter and a detector which is a lightdependent resistor.

If the light dependent resistor detects light, the relay switch is activated and the lift doorwill close.

Figure (b) shows an electronic circuit for the control system of the lift door.


27/27

Figure (b)

(i) State the relationship between the resistance and the intensity of light receivedby the light dependent resistor.

.

.. (ii) Complete the circuit in Figure (b), by drawing the resistor and the lightdependent resistor using the symbols given below.

(iii)

Explain how the circuit functions.

..

..

..

..

50

electronics chapter 4

Documents

Transcript of electronics chapter 4