APLICATIONS OF LOGIC GATES
STREET LIGHTS
On = 1
Off = 0
On = 1
Off = 0
Switch
Street light
Dark = 0
Bright = 1
Light sensor
(LDR)
Operational conditions
Author : Khairi
APLICATIONS OF LOGIC GATES
STREET LIGHTS
On = 1
Off = 0
On = 1
Off = 0
Switch
Street light
Dark = 0
Bright = 1
Light sensor
(LDR)
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
Dark = 1
Bright = 0
On = 1
Off = 0
Light sensor
Off (intruder) = 1
On (no intruder) = 0
1 0
Alarm
(siren)
Infrared
sensor
Operational conditions
Author : Khairi
APLICATIONS OF LOGIC GATES
SECURITY ALARM
Dark = 1
Bright = 0
On = 1
Off = 0
Light sensor
1 0
Off (intruder) = 1
On (no intruder) = 0
Alarm
(siren)
Infrared
sensor
Truth table
Light
sensor
Infrared
sensor
Alarm
Dark
Intruder
On
Dark
No intruder
Off
Bright
Intruder
Off
Bright
No intruder
Off
Author : Khairi
APLICATIONS OF LOGIC GATES
EXERCISE
Automatic fan control system
Heat detector
Hot = 1
Cold = 0
fan
On = 1
Off = 0
LDR
Daytime = 1
Night time = 0
Construct a truth table for the system above to show the operating
principle of the system
Author : Khairi
APLICATIONS OF LOGIC GATES
EXERCISE
Automatic fan control system
Heat
TIME
FAN
0
0
OFF
0
1
OFF
1
0
OFF
1
1
ON
Author : Khairi
APLICATIONS OF LOGIC GATES
EXERCISE
Fire alarm security system
USED THE OR GATE
Heat detector
Hot = 1
Cold = 0
siren
On = 1
Off = 0
Smoke detector
Smoke = 1
No smoke = 0
The system shown is not functioning well.Suggest a modification
in order to make the system works.
Author : Khairi
PAST YEARS QUESTION
Motor is activate when
some one press any one of
the button
a. Complete the truth table below
0
1
1
0
Author : Khairi
PAST YEARS QUESTION
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)
Author : Khairi
PAST YEARS QUESTION
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
Author : Khairi
PAST YEARS QUESTION
Infrared sensor is switch on
when a person crosses the
sensor at night
e. Complete the truth table by using the key given.
0
1
1
1
0
1
0
0
0
1
Author : Khairi
PAST YEARS QUESTION
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.
Author : Khairi