This is a traffic light finite state machine demonstration / challenge. Debug it and do the challenges at the end of the code.

traffic-light-challenge.ino

// Copyright 2020 Jean-Philippe Gravel <jeanphilippe.gravel@gmail.com>

// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in
// the Software without restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
// Software, and to permit persons to whom the Software is furnished to do so,
// subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
// PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.



// make unsigned long declaration shorter.
#define ulong unsigned long


// state values of the finite state machine
#define STATE_TRAFFIC_NS            1
#define STATE_TRAFFIC_NS_YELLOW     2
#define STATE_PEDESTRIANS           4
#define STATE_TRAFFIC_EW            8
#define STATE_TRAFFIC_EW_YELLOW    16


// arduino pin definition

// EAST/WEST lights
#define PIN_RED_EW    13
#define PIN_YELLOW_EW 12
#define PIN_GREEN_EW  11

// NORTH/SOUTH lights
#define PIN_RED_NS    10
#define PIN_YELLOW_NS  9
#define PIN_GREEN_NS   8

// pedestrians all directions
#define PIN_PEDESTRIANS 7 


// global variable declaration.
int   _state;
ulong _begin_time;


void setup() {
  pinMode(PIN_RED_NS,      OUTPUT);
  pinMode(PIN_YELLOW_NS,   OUTPUT);
  pinMode(PIN_GREEN_NS,    OUTPUT);
  pinMode(PIN_PEDESTRIANS, OUTPUT);
  pinMode(PIN_RED_EW,      OUTPUT);
  pinMode(PIN_YELLOW_EW,   OUTPUT);
  pinMode(PIN_GREEN_EW,    OUTPUT);
  
  _state = STATE_PEDESTRIANS;
  _begin_time = millis();
}

void loop() {
  ulong end_time = millis();
  ulong elapsed  = end_time - _begin_time;


  switch(_state) {

    case STATE_TRAFFIC_NS:
      digitalWrite(PIN_GREEN_NS,    HIGH);
      digitalWrite(PIN_YELLOW_NS,   LOW);
      digitalWrite(PIN_RED_NS,      LOW);
      digitalWrite(PIN_PEDESTRIANS, LOW);
      digitalWrite(PIN_GREEN_EW,    LOW);
      digitalWrite(PIN_YELLOW_EW,   LOW);
      digitalWrite(PIN_RED_EW,      HIGH);
      if (elapsed > 60000) {
        _state = STATE_TRAFFIC_NS_YELLOW;
        _begin_time = end_time;
      }
    break;

    case STATE_TRAFFIC_NS_YELLOW:
      digitalWrite(PIN_GREEN_NS,    LOW);
      digitalWrite(PIN_YELLOW_NS,   HIGH);
      digitalWrite(PIN_RED_NS,      LOW);
      digitalWrite(PIN_PEDESTRIANS, LOW);
      digitalWrite(PIN_GREEN_EW,    LOW);
      digitalWrite(PIN_YELLOW_EW,   LOW);
      digitalWrite(PIN_RED_EW,      HIGH);
      if (elapsed > 10000) {
        _state = STATE_PEDESTRIANS;
        _begin_time = end_time;
      }
    break;

    case STATE_PEDESTRIANS:
      digitalWrite(PIN_GREEN_NS,    LOW);
      digitalWrite(PIN_YELLOW_NS,   LOW);
      digitalWrite(PIN_RED_NS,      HIGH);
      digitalWrite(PIN_PEDESTRIANS, HIGH);
      digitalWrite(PIN_GREEN_EW,    LOW);
      digitalWrite(PIN_YELLOW_EW,   LOW);
      digitalWrite(PIN_RED_EW,      HIGH);
      if (elapsed > 60000) {
        _state = STATE_TRAFFIC_EW;
        _begin_time = end_time;
      }
    break;

    case STATE_TRAFFIC_EW:
      digitalWrite(PIN_GREEN_NS,    LOW);
      digitalWrite(PIN_YELLOW_NS,   LOW);
      digitalWrite(PIN_RED_NS,      HIGH);
      digitalWrite(PIN_PEDESTRIANS, LOW);
      digitalWrite(PIN_GREEN_EW,    HIGH);
      digitalWrite(PIN_YELLOW_EW,   LOW);
      digitalWrite(PIN_RED_EW,      LOW);
      if (elapsed > 60000) {
        _state = STATE_TRAFFIC_EW_YELLOW;
        _begin_time = end_time;
      }
    break;

    case STATE_TRAFFIC_EW_YELLOW:
      digitalWrite(PIN_GREEN_NS,    LOW);
      digitalWrite(PIN_YELLOW_NS,   LOW);
      digitalWrite(PIN_RED_NS,      HIGH);
      digitalWrite(PIN_PEDESTRIANS, LOW);
      digitalWrite(PIN_GREEN_EW,    LOW);
      digitalWrite(PIN_YELLOW_EW,   HIGH);
      digitalWrite(PIN_RED_EW,      LOW);
      if (elapsed > 10000) {
        _state = STATE_TRAFFIC_NS;
        _begin_time = end_time;
      }
    break;
    
  }

  // Challenge #0: This code is untested. Make sure it runs as expected 
  //               before stepping into challenge 1. Fix any issue you 
  //               find until the complete light cycle works. This is not
  //               a catch, it could work as is... or not.
  //
  // Challenge #1: Make the pedestrian light flash at 2 hertz for 
  //               the last 15 seconds of its cycle.
  //
  // Challenge #2: Do not enter the STATE_PEDESTRIANS state unless
  //               a pedestrian crossing request button is pressed.
  //
  // Challenge #3: Add a car detection input to on both north and south lanes.
  //               After the standard 1 minute EAST/WEST traffic time counter 
  //               elapsed, keep the east-west traffic running until a car
  //               is detected on the north OR south lane. Cycle into
  //               STATE_TRAFFIC_NS for one minute and continue the cycle.
}