3. 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
5. OR GATE
Front Doorbell Switch
Back Doorbell Switch
Doorbell
ON/OFF
ON/OFF
ON/OFF
If either the Front Doorbell Switch
OR the Back Doorbell Switch is
pressed then the Doorbell rings.
7. AND GATE
Person Sensor
Alarm Switch
Burglar Alarm
ON/OFF
ON/OFF
ON/OFF
If both the Person Sensor AND
the Alarm Switch are on then the
Burglar Alarm is activated.
8. NOT GATE
A XINPUT OUTPUT
A NOT gate (inverter) has only one input. It reverses the logic state.
9. 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.