Truth tables

AND Gate

Input 1 Input 2

0 0

1 0

0 1

1 1

output

0

0

0

1

output

?

?

?

?

Input 1 Input 2

0 0

1 0

0 1

1 1

output

?

?

?

?

output

0

1

1

1

OR Gate

Truth tables

NAND Gate

Input 1 Input 2

0 0

1 0

0 1

1 1

output

1

1

1

0

output

?

?

?

?

Input 1 Input 2

0 0

1 0

0 1

1 1

output

?

?

?

?

output

1

0

0

0

NOR Gate

INPUT PROCESS OUTPUT

Thermister LOGIC

GATES

Buzzer

LDR Bulb

Switch

PARTS OF A SYSTEM

Simple system – Alarm when it is hot and a window is closed

Push SwitchDown = ?

Up = ?

Thermister

Hot = ?

Cold = ?

Down = 1

Up = 0

Hot = 1

Cold = 0

Gate? Buzzer

Simple system – Alarm when it is COLD and a window is closed

Push Switch

Thermister

Down = 1

Up = 0

Hot = 1

Cold = 0

Gate?

Buzzer

The most complicated diagram you could be asked

Thermister

On/off Switch

LDR

Light a bulb when it is HOT and DARK and a swtich is turned on

Hot = 1

Cold = 0

Light = 1

On = 1

Dark = 0

off = 0

First step?

Second step?

Last step?

The Bistable or Latch gate

You are only ever expected to say how it works like this:

1. When SET becomes on the output switches ON……..

SET

RESET

output

2. Even if SET becomes off the output stays ON

3. If the RESET becomes on the output becomes OFF