Clock Time

Author

Affiliation

Dr Chris Jobling

Department of Electronic and Electrical Engineering

Published

November 1, 2023

Brief: to produce a clock display with hours, minutes, seconds display plus day of week.

The minimum requirement will be to have a digital clock display which advances at the correct rate.

Additional marks for the degree of sophistication of the timer functions, for example multiple events; one-off and regular events; and GMT/BST switching. Additional hardware will be provided in the form of relays to drive the load.

The starting point for this project is Getting Started with the Time Clock Project. It shows you how to set the epoch time for a clock, adjust it to clock time and then display the time in hours minutes and seconds. The display code is similar to the code used in Experiment 1: Binary Counter.

After that is done, you need to add inputs and outputs and additional functionality to allow for setting the time, setting alarms, creating timers and stop watches, etc.

Marks will be awarded as follows:

0 to 40%: If some kind of activity is seen on the LCD.
40 to 50%: If the display is formatted into hours, minutes etc. and advances correctly.
50 to 60%: If there is at least one relay driven on and off at specified time.
60 to 70%: For more advanced timer functions.
70% plus: For additional functionality such as daily, weekly events.

Getting Started with the Time Clock Project

Starter code

The starter code starts the clock at an arbitrary time and then uses the millis() function to keep the clock time synchronised to the initial epoch time. I have used the Serial monitor for the output and you will need to change the code to use the LCD panel.

The Serial monitor is still useful during development and for debugging though!

Your first task will be to set the initial time in the setup() function before you press the button on pin 2 or Port D to set the clock time. After that, the clock time should keep reasonable time based on the epoch time stored in epoch_time.

// Define times in millis as useful constants
#define MILLIS_PER_SECOND 1000
#define MILLIS_PER_MINUTE 60 * MILLIS_PER_SECOND
#define MILLIS_PER_HOUR 60 * MILLIS_PER_MINUTE
#define MILLIS_PER_DAY 24 * MILLIS_PER_HOUR

unsigned long epoch_time, initial_time, clock_time;
unsigned int days, hours, minutes, seconds, milli_seconds;

// The setup function runs once when you press reset or power the board
// Use it to set the time and record the realtime offset
void setup() {

  Serial.begin(9600);
  Serial.println("Set time then press button when ready");

  pinMode(2, INPUT_PULLUP);  // Make bit 2 of Port D an input

  // Initial time is arbitrarily set to 12:15:35:101
  hours = 12;
  minutes = 15;
  seconds = 35;
  milli_seconds = 101;
  initial_time = hours * MILLIS_PER_HOUR + minutes * MILLIS_PER_MINUTE + seconds * MILLIS_PER_SECOND + milli_seconds;
  Serial.print("Epoch offset: ");
  Serial.println(initial_time);
  
  /* Write code to accept values entered from clock diaplay 
     and use button press as a go signal */
  while ((PIND & 0b00000100) != 0) {
    Serial.println("Waiting ...");
    break;
  }
  Serial.println("Go ...");
  epoch_time = millis();
  Serial.print("Epoch time: ");
  Serial.println(epoch_time);
}

// the loop function runs over and over again forever

void loop() {

  clock_time = millis() + initial_time;
  Serial.print("Clock time: ");
  Serial.println(clock_time);

  // Because of the delay, the clock display will update each second approximately.
  // There could be some drift here - so it's best to compute the time rather
  // than relying on the instructions given to update hh:mm:ss.
  // As supplied, the clock will go to 00:00:00 at midnight and the epoch will reset.
  // You can include days but note that millis() resets every 79 days or so.
  delay(1000);  // reduce this delay for faster counting
  seconds++;
  if (seconds > 59) {
    seconds = 0;
    minutes++;
    if (minutes > 59) {
      minutes = 0;
      hours++;
      if (hours > 23) {
        hours = 0;
        // days++;
        // reset epoch offset at midnight unless you want to track days too
        initial_time = millis();
      }
    }
  }
  Serial.print(hours);
  Serial.print(":");
  Serial.print(minutes);
  Serial.print(":");
  Serial.print(seconds);
  Serial.println(" ");
}

View and download the code from GitHub gist clock.ino.

Tips

Your program will benefit from the use of functions, e.g. to display current time you could write a function:

void display_time(int hours, int minutes, int hours) {
  Serial.print(hours);
  Serial.print(":");
  Serial.print(minutes);
  Serial.print(":");
  Serial.print(seconds);
  Serial.println(" ");
}

When you want to display the time you will just call

display_time(hours, minutes, seconds);

As you extend the clock, you will occasionally need to leave the main loop, e.g. to set an alarm. This means that the loop will not be updating the time while you are doing something else.

You will therefore need a function to compute the current clock time in elapsed hours, minutes and seconds from clock_time. How to do this is left as an exercise, but the MATLAB code clocks.mlx which you will find in my the shared MATLAB drive folder eg-151 may help help you to understand how you might do the computations needed.

Note that in MATLAB mod(11,2) is equivalent to the C code:

11 % 2; // = 1: remainder of 11/2

and floor(11,2) is equivalent to to the C code:

11 / 2; // = 5: integer division gives 5.5 rounded down to nearest integer

You will need both integer division and modulo division to convert a time defined in milliseconds elapsed into actual clock time in hours:minutes:seconds.