When we are working out what possibilities exist for a particular Boolean logic structure, we can use a truth table to represent that data.
Using the previous example we can produce a simple truth table for the results.
A Boolean AND gate works by the following rules:
- If both inputs are true, then the output will be True.
- Otherwise the output will be false
Challenge 1 – AND Gate truth table
Can you fill out the truth table for an AND gate?
A Boolean OR gate works by the following logic:
- If either input is True, the output is True.
- If both inputs are True, the output is True.
- Otherwise the output is false.
Challenge 2 – Can you work out the truth table for a Boolean OR gate?
A Boolean NOT gate simply reverses whatever input is given.
- If the input is True, the output is False
- If the input is False, the output is True
Scratch Not gate Example
Challenge 3 – Can you write a truth table for a NOT gate?
Have a go at connecting up multiple logic gates to see what happens, using the simulator below. Can you work out the inputs and outputs for the following examples.
Activity 2 – Applying Logic Gates
Using the link below, see if you can make the following systems:
System 1 – Fan cooling system.
If the main system switch is turned on, then the fan will operate when:
- Every 5 seconds
- When The manual override button is pressed.
System 2 – Basic Alarm System
Make a system where if any of the 3 sensors (use 3 switches to represent sensors) are triggered, the alarm light will flash RED.
System 3 – Advanced Alarm System
Adapt the system so that:
- The alarm will not be triggered if the system has not been armed first (use another switch for this)
- The alarm should alternate between flashing red and sound a siren every 1 second.
System 4 – Button operated traffic light.
Make a traffic light that starts on green, then goes to amber – red – amber – green again.
Hint – You’ll need to flip flop!