In this challenge, we will design, create and test a logic gates circuit to control a traffic lights made of 3 LEDs (Red Amber Green). This challenge is designed to be completed with a logic board such as the Logic & Arithmetic board designed by the University of Southampton and the UK Electronic Skills Foundation. You will be able to complete the circuit with just the Logic & Arithmetic board. However if you have access to breadboards and LEDs you will be able to create your own Red Amber Green traffic lights for a more realistic output.

Alternatively, if you do not have access to a physical kit, you can still complete these challenges using our online logic gates circuit simulator

#### Traffic Lights Sequence

A UK Traffic Lights follows a sequence of four different states:

In order to design a logic gates circuit for our traffic lights system we will need a circuit with two inputs (J and K) and 3 outputs (X, Y and Z). Our two inputs will give 4 different states to our circuit: 00, 01, 10 and 11. The following diagram shows the expected outputs for 4 possible states (input patterns):

#### Truth Table?

Your first task is to use the above diagram to complete the Truth Table for our Traffic Light Controller system:

Input J | Input K | Output X (Red) | Output Y (Amber) | Output Z (Green) |

0 | 0 | |||

0 | 1 | |||

1 | 0 | |||

1 | 1 |

#### Logic Gates Diagrams

Using the information from the completed Truth table we can then work out the logic gates circuits needed to control each output based on the two inputs J and K.

You can try to create this diagrams by yourself using logic.ly or our online Logic Gates Diagram designer tool.

Here are the individual diagrams:

**Output X: Red Light:**

**Output Y: Red Light:**

**Output Z: Red Light:**

All three diagrams can then be combined into a single diagram:

You can now recreate this circuit with your logic board:

#### Using RGB LEDs

The following diagram shows you how to connect your logic board to 3 LEDs on a breadboard.

Be careful when connecting your LEDs to detect where the anode and the cathode are on each LED:

#### Using Lego bricks…

You can also create your own traffic lights using Lego bricks and control them with your logic board!

#### Traffic Light Sequence using Logic Gates

By combining the above circuit with a 2-bit counter circuit, we can create a fully animated traffic light sequence. Click on the diagram below to test this circuit: