In this project you will build a traffic light controller using only registers $($D$-$flip flops$)$ and basic logic gates $($AND$,$ OR$,$ NAND, NOR, NOT$).$

The Problem

You are modeling the lights for a small north$/$south road making a T junction with a larger east$/$west road. For example, let's take the Summer St$.$ and Plymouth St$.$ intersection on campus:

There are two sets of lights: Red, Yellow, Green for the East$/$West$-$bound traffic, and Red, Yellow, Green for the northbound traffic. The light normally stays green for the East$/$West street unless a northbound car activates a switch. Let's say, for simplicity, that red lights last for $4$ seconds, green for $2$ seconds, yellow for $1$ second.

The state diagram for this problem looks like this:

Objective

Your objective is to design and construct a digital circuit to control these traffic lights. Your circuit will have one input $($is a northbound car waiting$)$ and six outputs: on$/$off for each light on the two traffic signals. You should design a circuit in the Emumaker$86$ simulator provided on Blackboard. For full credit, you should implement this circuit using an Arduino Uno and a breadboard.

Step $1$: Truth Table

Design a transition truth table for this traffic light controller. Your table should have $4$ inputs $(1$ switch, $3-$bit current state$)$ and $9$ outputs $(3-$bit next state, $6$ lights$).$

Step $2$: Equations

Make the full Sum$-$of$-$Products logic equations. There should be nine of them.

Step $3($optional but strongly encouraged$)$: Simplify

Simplify the equations as much as you can.

Step $4$: Build it

Build the circuit in the simulator. Use an input$-$pin for the car switch and six output pins for the lights. You may use either $1-$bit registers or NAND gates as D$-$flip$-$flops to store your state. The rest of your circuit must consist only of AND$/$OR$/$NAND$/$NOR$/$NOT gates and buses.

Step $5$: Test it

If you used a register for storage you should press Simulate, and press the STEP button once per second to cycle through the lights. If you chose to make your flip$-$flops out of registers, you will have an addition "Clock" input$-$pin that you will click to advance to the next state.

Submit your simulator save file to Blackboard.

Step $6$: Get the breadboard ready

Set up six LEDs $(2$ green, $2$ yellow, $2$ red$)$ and make sure that they are connected through a $1$k $($brown$-$black$-$red$)$ resistor to ground. If you are completing this at home, you will need to construct the oscillator circuit from Lab $1$ to drive the Clock input pin. Alternatively, if you can make it to school, then use the TTL clock output on one of the blue lab boards.

Step $7$: Install the software

Download the Arduino IDE from the web, install it$.$ Press the Export button and save your work to trafficlight.ino. Open it in the Arduino IDE. Upload it to an Uno.

Step $8$: Connect your Uno to the circuit

Look in the comments at the top of trafficlight.ino to see which pins correspond to which input and output pins in your circuit. Then connect the LEDs and the Clk $($or switch$)$ to the appropriate holes. Make sure that you connect GND on the breadboard to GND on the Uno. Does it work?