This document discusses logic gates and their functions. It describes three basic logic gates: AND gates, OR gates, and NOT gates. AND gates only output true if both inputs are true. OR gates output true if either input is true. NOT gates reverse the input logic state. Examples are given for each gate type.

1. LOGIC GATES
Lesson Objectives:
• To understand the function of Logic Gates

2. A logic gate is a digital circuit which either allows a
signal to pass through it or to stop it.
There are three basic logic gates: AND, OR and NOT.
AND GATE
OR GATE
NOT GATE

3. OR GATE
INPUT
A
X
INPUT
OUTPUT
B
The output will be positive (True) if at least one input is true.

4. OR GATE
ON/OFF
Front Doorbell Switch
Doorbell
Back Doorbell Switch
ON/OFF
ON/OFF
If either the Front Doorbell Switch
OR the Back Doorbell Switch is
pressed then the Doorbell rings.

5. AND GATE
INPUT
A
X
INPUT
OUTPUT
B
The output will be positive (true) when both inputs (the input one AND the input two)
are positive (true).

6. AND GATE
ON/OFF
Person Sensor
Burglar Alarm
Alarm Switch
ON/OFF
If both the Person Sensor AND
the Alarm Switch are on then the
Burglar Alarm is activated.
ON/OFF

7. NOT GATE
INPUT
A
X
OUTPUT
A NOT gate (inverter) has only one input. It reverses the logic state.

8. NOT GATE
Temperature Detector
(Above 20°C)
Central Heating
ON/OFF
ON/OFF
If the temperature is above 20°C
then the Central Heating is
switched off.
If the temperature is below 20°C
then the Central Heating is
switched on.