Author : Khairi

APLICATIONS OF LOGIC GATES

Switch

Light sensor

(LDR)

Street light

STREET LIGHTS

On = 1

Off = 0

Dark = 0

Bright = 1

On = 1

Off = 0

Operational conditions

Author : Khairi

APLICATIONS OF LOGIC GATES

Switch

Light sensor

(LDR)

Street light

STREET LIGHTS

On = 1

Off = 0

Dark = 0

Bright = 1

On = 1

Off = 0

Truth table

Switch LDR Street light

On Dark On

On Bright On

Off Dark On

Off Bright Off

Author : Khairi

APLICATIONS OF LOGIC GATES

SECURITY ALARM

Light sensor

Infrared

sensor

Alarm

(siren)1 0

Operational conditions

Dark = 1

Bright = 0

Off (intruder) = 1

On (no intruder) = 0

On = 1

Off = 0

Author : Khairi

APLICATIONS OF LOGIC GATES

SECURITY ALARM

Light sensor

Infrared

sensor

Alarm

(siren)1 0

Dark = 1

Bright = 0

Off (intruder) = 1

On (no intruder) = 0

On = 1

Off = 0

Truth table

Light

sensor

Infrared

sensorAlarm

Dark Intruder On

Dark No intruder Off

Bright Intruder Off

Bright No intruder Off

Author : Khairi

EXERCISE

Automatic fan control system

Heat detector

LDR

fan

Hot = 1

Cold = 0

Daytime = 1

Night time = 0

On = 1

Off = 0

Construct a truth table for the system above to show the operating

principle of the system

APLICATIONS OF LOGIC GATES

Author : Khairi

Heat TIME FAN

0 0 OFF

0 1 OFF

1 0 OFF

1 1 ON

APLICATIONS OF LOGIC GATES

Automatic fan control system

EXERCISE

Author : Khairi

Fire alarm security system

Heat detector

Smoke detector

siren

Hot = 1

Cold = 0

Smoke = 1

No smoke = 0

On = 1

Off = 0

The system shown is not functioning well.Suggest a modification

in order to make the system works.

USED THE OR GATE

APLICATIONS OF LOGIC GATESEXERCISE

Author : Khairi

a. Complete the truth table below

0

1

1

0

Motor is activate when

some one press any one of

the button

PAST YEARS QUESTION

Author : Khairi

Diagram shows a security system using infrared sensor.

a. If the potential difference across resistor W is 2 V.

What is the potential difference across infrared sensor ?

10 V

b. Component X has a high resistance when the surrounding are dark

and a low resistance in bright surroundings.Name the component X.

Light Dependence Resistor (LDR)

PAST YEARS QUESTION

Author : Khairi

Diagram shows a security system using infrared sensor.

Component S is a switch that connects the 240 V a.c spotlight.

c. Name the component S.

Relay

d. Why is component S necessary in the circuit ?

To switch the spotlight in secondary circuit

PAST YEARS QUESTION

Author : Khairi

0

1

1

1

0

1

Infrared sensor is switch on

when a person crosses the

sensor at night

e. Complete the truth table by using the key given.

0

0

0

1

PAST YEARS QUESTION

Author : Khairi

Infrared sensor is switch on

when a person crosses the

sensor at night

f. Name the correct logic gate for the system.

AND gate

g. Sketch the symbol for the logic gate.

PAST YEARS QUESTION