Traffic light time to Green - Count down - Arduino Forum

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I need some help with working out... A) If this is possible and if it is...B) How the script would be written?

I am constructing a 2/3 size real working pair of traffic lights, to be used to enable cars etc to pass through a narrow section of private roadway, where only one vehicle at a time can pass through. Usual UK system of Red-Red/Amber-Green to Amber then Red. The timing of the lights operation is all done and I have a set already working correctly, but I would like to add to each traffic light head a two digit count down display which advises any waiting vehicle that the Green will become available in XX seconds (Decreasing from 99 to 0). I hope to use a couple of Uno's I have - one in each head and trigger their timing via the traffic lights red aspect initially being lit. The counter displays are two digit seven segment common Cathode 0.56". So timing starts on the red being lit, but has to begin at 130 seconds as that is the time interval from initially going to red then that light eventually going to green. So the count down digits won't light until the timer has reached 99 seconds then counts down to 0 and the green aspect lights and the counting display turns off and resets ready for the red to trigger it again.

Is such possible? If so, can anyone offer guidance on the script needed?

Many thanks for reading the above and hopefully helping.

Hi

I do not have sketch, hence my question. Is one readily available that perhaps could be modified?
Timing for each heads would only be started when that heads red aspect is initially lit. Once at green the Uno would reset and wait for the next red.

The two Uno's, if used, do not need to be synced, as above, the timing is only started when that head has its red LED aspect initally lit.

The two heads will be approx. 120-150 Yds apart on an 80 degree road bend with a building on the corner obscuring views and the road width of approx. a Transit style van. Hence the need for traffic management.

The traffic lights are already working (On test only) via a 4 core cable to each head from the lights control centre. Cable core 1 = Red feed, Core 2 Amber feed, Core 3 Green feed and Core 4 Return - 24 volt DC.
I just thought adding a countdown display might be useful, but its not essential. My idea was that a vehicle waiting at the red traffic light may not know how long they have to wait.

#Please note this a small private access road, with a few cars / vans etc an hour. But one vehicle leaving can cause issues currently if it meets an unseen (due to the corner and building ) an incoming vehicle. Hence the need for traffic lights that cycle through their sequence every 130 seconds.

I slightly modified @6v6gt's code to be non-blocking. This allows standing up a traffic lights sequencer beside that code to make a fully automatic demo.

For more traffic light with countdown timerinformation, please contact us. We will provide professional answers.

Since life is so short, I severely cut down all the time constants. It should work fine with the numbers changed to reflect real life timing.

In the wokwi, there is one function call in loop() and one in setup() to implement the traffic lights. In the schematic, the squiggly orange wire is the only connection between the countdown stuff and the traffic lights sequencer.

Play with it here:

traffic and lights

Code. I had to change the sense of the input to @6v6gt's algorithm. I also notice that just looking at the red light results in some potential flaws arising. Here, for example, I note that the countdown number remains at zero, and on display, during the RED/AMBER period.

// https://wokwi.com/projects/
// https://forum.arduino.cc/t/traffic-light-time-to-green-count-down/

#include 

const uint8_t redPin = 4 ;
const uint8_t ledPin = 7 ;

bool lastRedState = HIGH ;
uint16_t counter = 0 ;
uint32_t lastSecs = 0 ;

LiquidCrystal_I2C  lcd(0x27, 16, 2);

void setup() {
  Serial.begin();
  pinMode(redPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT );
  lcd.init( );
  lcd.backlight();

  setupTrafficLights();
}

void loop() {

  serviceTrafficLights();

// to only run the traffic lights, just  return; right here

  bool redState = !digitalRead( redPin ) ;  // true logic now
  uint32_t secs = millis() /  ;
  if ( redState == LOW ) {
    digitalWrite(ledPin, HIGH);
    if ( secs != lastSecs ) {
      lastSecs = secs ;
      if ( counter > 0 ) counter-- ;
    }

    if ( lastRedState == HIGH ) {
      lastRedState = redState ;
      counter = 15 ;   // should be 130. Life too short
    }

    static uint16_t onDisaply = 999;    // impossible previous value
//    if ((counter < 100) && (counter != onDisaply)) {
    if ((counter < 10) && (counter != onDisaply)) {
      lcd.clear();
      lcd.print( counter );
      onDisaply = counter;
    }
  }
  else {
    // clear up
    lcd.clear() ;
    digitalWrite(ledPin, LOW);
    lastRedState = HIGH ;
  }
}






// code to create a set of traffic lights to inform the coutdown process

// non-blocked traffic light sequencer
// "Usual UK system of Red     Red/Amber      Green     Amber   "

// three outputs for the simulated traffic lights
const uint8_t redLight = 8;
const uint8_t yellowLight = 9;
const uint8_t greenLight = 10;

enum {RED, REDAMBER, GREEN, AMBER};

const unsigned long times[4] = {, , , };  // in milliseconds here

void setupTrafficLights()
{
  pinMode(redLight, OUTPUT);
  pinMode(yellowLight, OUTPUT);
  pinMode(greenLight, OUTPUT);
}

void serviceTrafficLights()
{
  static unsigned char phase = 0;
  static unsigned long waitFrom;

  unsigned long now = millis();

  if (waitFrom && now - waitFrom < times[phase]) return;

  phase++; if (phase >= 4) phase = 0;
  waitFrom = now;

  switch(phase) {
  case RED :
    digitalWrite(redLight, HIGH);
    digitalWrite(yellowLight, LOW);
    digitalWrite(greenLight, LOW);

    break;

  case REDAMBER :
    digitalWrite(redLight, HIGH);
    digitalWrite(yellowLight, HIGH);
    digitalWrite(greenLight, LOW);

    break;

  case GREEN :
    digitalWrite(redLight, LOW);
    digitalWrite(yellowLight, LOW);
    digitalWrite(greenLight, HIGH);

    break;

  case AMBER :
    digitalWrite(redLight, LOW);
    digitalWrite(yellowLight, HIGH);
    digitalWrite(greenLight, LOW);

    break;

  default :
  // yes, this did show up, so
    Serial.println("logic error somewhere");
  }
}

a7

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