Accurate Clock Just Using an Arduino

1// Paul Brace - Feb 2021
2// Simple Clock with Date created just using   a Arduino - no RTC module
3// Program incorporates a time correction adjustment   to compensate for the internal
4// clock speed not being 100% accurate.
5//   Once correct speed adjustment set the clock is surprisingly accurate.
6// In my   test it did not lose or gain any time over a 5 day period.
7// Displays time on   a 16x2 LCD display
8// Buttons to set time
9//   Mode button (pin 2) toggles   set time, set date and run
10//   Button 1 (pin 3) Increments Minutes and Month   and decreases Year/speed adj
11//   Button 2 (pin 4) Increments Hour and Day and   increases Year./speed adj
12// 24 Hour display
13
14// Include the library driver   for display:
15#include <LiquidCrystal.h>
16
17// LiquidCrystal lcd( RS, EN,   D4,D5, D6, D7)
18LiquidCrystal lcd(12, 13, 6, 7, 8, 9); // create an lcd object   and assign the pins
19
20// Define buttons and buzzer connections
21#define MODE_BUTTON   2
22#define HOUR_BUTTON 3                  // Same button different definitions   to
23#define UP_BUTTON 3                    // make code easier to understand 
24#define   DAY_BUTTON 3
25#define MINUTE_BUTTON 4                // Same button different   definitions to
26#define DOWN_BUTTON 4                  // make code easier to   understand 
27#define MONTH_BUTTON 4
28
29// Current mode settings
30#define   SHOW_TIME 1                    // 1 = running - show time
31#define SET_TIME  2                     // 2 = time set
32#define SET_YEAR  3                    //   3 = year set
33#define SET_DATE  4                    // 4 = day/month set 
34#define   SET_SPEED_ADJ  5               // 5 = amend the speedCorrection variable
35
36int   speedCorrection = 3545;            // Number of milliseconds my Nano clock runs   slow per hour
37// negative number here if it is running fast
38// change to match   your Arduino
39
40// Volatile variables as changed in an interrupt and we
41//   need to force the system to read the actual variable
42// when used outside the   interrupt and not use a cached version
43volatile unsigned long currentTime;    //   Duration in milliseconds from midnight
44unsigned long lastTime = -1000;        //   lastTime that ShowTime was called initialised to -1000 so shows immediately
45volatile   unsigned long elapsed;        // Timer used for delay and hour count
46
47unsigned   long millisecondsInADay;      // Milliseconds in 24 hours
48unsigned long millisecondsInHour;       // Milliseconds in 1 hour
49int currentMode;                       // 1 =   running - show time
50// 2 = time set
51// 3 = year set
52// 4 = day/month set
53
54float   currentDate;                     // Julian date
55float lastDate = 0.0;                  //   last date that ShowDate was called
56int currentDay;
57int currentMonth;
58int   currentYear;
59
60char *dayArray[] = {  "Tue.  ",       // Will show a compiler   warning but works fine
61                      "Wed.  ",
62                      "Thur.   ",
63                      "Fri.  ",
64                      "Sat.  ",
65                       "Sun.  ",
66                      "Mon.  "
67                   };
68
69void   setup() {
70  // Set up  time interrupt - millis() rolls over after 50 days so
71   // we are using our own millisecond counter which we can reset at
72  // the   end of each day
73  TCCR0A = (1 << WGM01);      //Set the CTC mode Compare time   and trigger interrupt
74  OCR0A = 0xF9;               //Set value for time to compare   to ORC0A for 1ms = 249  (8 bits so max is 256)
75  //[(Clock speed/Prescaler value)*Time   in seconds] - 1
76  //[(16,000,000/64) * .001] - 1 = 249 = 1 millisecond
77  TIMSK0   |= (1 << OCIE0A);    //set timer compare interrupt
78  TCCR0B |= (1 << CS01);      //Set   the prescale 1/64 clock
79  TCCR0B |= (1 << CS00);      // ie 110 for last 3 bits
80   TCNT0  = 0;                 //initialize counter value to 0
81  sei();                      //Enable   interrupt
82
83  pinMode(MINUTE_BUTTON, INPUT_PULLUP);
84  pinMode(HOUR_BUTTON,   INPUT_PULLUP);
85  pinMode(MODE_BUTTON, INPUT_PULLUP);
86  //pinMode(BUZZER, OUTPUT);
87   currentTime = 0;                          // Set to current time to mindnight
88   currentDate = JulianDate(1, 1, 2021);     // Set base date
89  elapsed = 0;                              //   Set period counter to 0
90  millisecondsInADay = 24ul * 60 * 60 * 1000;
91  millisecondsInHour   = 60ul * 60 * 1000;
92  currentMode = SHOW_TIME;                  // Initial mode   is running and showing time and date
93  // Setup LCD
94  lcd.begin(16, 2);
95   lcd.noAutoscroll();
96  lcd.display();
97  lcd.clear();
98  ShowTime(currentTime);
99}
100
101void   loop() {
102  // loop runs every 150 milliseconds
103
104  // If at end of the day   reset time and increase date
105  if ((currentMode == SHOW_TIME) &&
106      (currentTime   > millisecondsInADay)) {
107    //Next day
108    // Stop interrupts while reset   time
109    noInterrupts();
110    currentTime -= millisecondsInADay;
111    interrupts();
112     currentDate++;
113  }
114  // At the end of each hour adjust the elapsed time   for
115  // the inacuracy in the Arduino clock
116  if (elapsed >= millisecondsInHour)   {
117    noInterrupts();
118    // Adjust time for slow/fast running Arduino clock
119     currentTime += speedCorrection;
120    // Reset to count the next hour
121    elapsed   = 0;
122    interrupts();
123  }
124
125  // Check if any buttons have been pressed
126   CheckButtons();
127
128  // Show display based on current mode
129  switch (currentMode)   {
130    case SHOW_TIME:
131      // Display current time and date
132      ShowTime(currentTime);
133       ShowDate(currentDate);
134      break;
135    case SET_TIME:
136      // Display   screen for setting the time
137      ShowTimeSet(currentTime);
138      break;
139     case SET_YEAR:
140      // Display screen for setting the year
141      ShowYearSet(currentDate);
142       break;
143    case SET_DATE:
144      // Display screen for setting the day   and month
145      ShowDDMMSet(currentDate);
146      break;
147    case SET_SPEED_ADJ:
148       // Display screen for adjusting the speed correction
149      ShowSpeedSet();
150       break;
151  }
152  Wait(150);
153}
154
155// This is interrupt is called when   the compare time has been reached
156// hence will be called once a millisecond   based on the
157// OCR0A register setting.
158ISR(TIMER0_COMPA_vect) {
159  if (currentMode   != SET_TIME)
160    currentTime++;
161  elapsed++;
162}
163
164float JulianDate(int   iday, int imonth, int iyear) {
165  // Calculate julian date (tested up to the year   20,000)
166  unsigned long d = iday;
167  unsigned long m = imonth;
168  unsigned   long y = iyear;
169  if (m < 3) {
170    m = m + 12;
171    y = y - 1;
172  }
173   unsigned long t1 = (153 * m - 457) / 5;
174  unsigned long t2 = 365 * y + (y /   4) - (y / 100) + (y / 400);
175  return 1721118.5 + d + t1 + t2;
176}
177
178void   GregorianDate(float jd, int &iday, int &imonth, int &iyear) {
179  // Note 2100   is the next skipped leap year - compensates for skipped leap years
180  unsigned   long f = jd + 68569.5;
181  unsigned long e = (4.0 * f) / 146097;
182  unsigned   long g = f - (146097 * e + 3) / 4;
183  unsigned long h = 4000ul * (g + 1) / 1461001;
184   unsigned long t = g - (1461 * h / 4) + 31;
185  unsigned long u = (80ul * t) /   2447;
186  unsigned long v = u / 11;
187  iyear = 100 * (e - 49) + h + v;
188  imonth   = u + 2 - 12 * v;
189  iday = t - 2447 * u / 80;
190}
191
192void SplitTime(unsigned   long curr, unsigned long &ulHour,
193               unsigned long &ulMin, unsigned   long &ulSec) {
194  // Calculate HH:MM:SS from millisecond count
195  ulSec = curr   / 1000;
196  ulMin = ulSec / 60;
197  ulHour = ulMin / 60;
198  ulMin -= ulHour   * 60;
199  ulSec = ulSec - ulMin * 60 - ulHour * 3600;
200}
201
202unsigned long   SetTime(unsigned long ulHour, unsigned long ulMin,
203                      unsigned   long ulSec) {
204  // Sets the number of milliseconds from midnight to current time
205   return (ulHour * 60 * 60 * 1000) +
206         (ulMin * 60 * 1000) +
207         (ulSec   * 1000);
208}
209
210void Wait(unsigned long value) {
211  // Create our own dealy   function
212  // We have set our own interrupt on TCCR0A
213  // hence millis()   and delay() will no longer work
214  unsigned long startTime = elapsed;
215  while   ((elapsed - startTime) < value) {
216    // Just wait
217  }
218}
219
220void CheckButtons()   {
221  // If the mode button has been pressed pin will go LOW
222  if (digitalRead(MODE_BUTTON)   == LOW) {
223    // Advance to next mode
224    switch (currentMode) {
225      case   SHOW_TIME:
226        currentMode = SET_TIME;
227        lcd.clear();
228        break;
229       case SET_TIME:
230        currentMode = SET_YEAR;
231        lcd.clear();
232         break;
233      case SET_YEAR:
234        currentMode = SET_DATE;
235        lcd.clear();
236         break;
237      case SET_DATE:
238        currentMode = SET_SPEED_ADJ;
239         lcd.clear();
240        break;
241      case SET_SPEED_ADJ:
242        currentMode   = SHOW_TIME;
243        lcd.clear();
244        // Reset variables so that the display   will be forced to update
245        // the next time ShowTime and ShowDate are called
246         lastTime = 0;
247        lastDate = 0.0;
248        break;
249    }
250   }
251  if (currentMode != SHOW_TIME) {
252    switch (currentMode) {
253      //   If mode anyhting other than SHOW_TIME check buttons
254      // Pin goes LOW when   ssociated button pressed
255      case SET_TIME:
256        if (digitalRead(MINUTE_BUTTON)   == LOW) {
257          // Advance minute
258          unsigned long iHours;
259           unsigned long iMinutes;
260          unsigned long iSeconds;
261          SplitTime(currentTime,   iHours, iMinutes, iSeconds);
262          if (iMinutes < 59) {
263            iMinutes++;
264           }
265          else {
266            iMinutes = 0;
267          }
268           // Set stored milliseconds based on current setting
269          noInterrupts();
270           currentTime = SetTime(iHours, iMinutes, 0);
271          elapsed = 0;
272           interrupts();
273        }
274        if (digitalRead(HOUR_BUTTON) ==   LOW) {
275          // Advance hour
276          unsigned long iHours;
277          unsigned   long iMinutes;
278          unsigned long iSeconds;
279          SplitTime(currentTime,   iHours, iMinutes, iSeconds);
280          if (iHours < 23) {
281            iHours++;
282           }
283          else {
284            iHours = 0;
285          }
286          //   Set stored milliseconds based on current setting
287          noInterrupts();
288           currentTime = SetTime(iHours, iMinutes, 0);
289          elapsed = 0;
290           interrupts();
291        }
292        break;
293      case SET_YEAR:
294         if (digitalRead(UP_BUTTON) == LOW) {
295          // Increase year
296          int   iDay;
297          int iMonth;
298          int iYear;
299          GregorianDate(currentDate,   iDay, iMonth, iYear);
300          iYear++;
301          // Set stored date based   on current settings
302          currentDate = JulianDate(iDay, iMonth, iYear);
303         }
304        if (digitalRead(DOWN_BUTTON) == LOW) {
305          // Decrease   year
306          int iDay;
307          int iMonth;
308          int iYear;
309           GregorianDate(currentDate, iDay, iMonth, iYear);
310          iYear--;
311           // Set stored date based on current settings
312          currentDate   = JulianDate(iDay, iMonth, iYear);
313        }
314        break;
315      case   SET_DATE:
316        if (digitalRead(MONTH_BUTTON) == LOW) {
317          // Advance   month
318          int iDay;
319          int iMonth;
320          int iYear;
321           GregorianDate(currentDate, iDay, iMonth, iYear);
322          iMonth++;
323           if (iMonth > 12) {
324            iMonth = 1;
325          }
326          //   Set stored date based on current settings
327          currentDate = JulianDate(iDay,   iMonth, iYear);
328        }
329        if (digitalRead(DAY_BUTTON) == LOW) {
330           // Advance day
331          int iDay;
332          int iMonth;
333          int   iYear;
334          GregorianDate(currentDate, iDay, iMonth, iYear);
335          iDay++;
336           if (iDay > 31) {
337            iDay = 1;
338          }
339          if   (((iMonth == 4) || (iMonth == 6) || (iMonth == 9) || (iMonth == 11))
340              &&   (iDay > 30)) {
341            iDay = 1;
342          }
343          if ((iMonth   == 2) && (iDay > 29)) {
344            iDay = 1;
345          }
346          if   ((iMonth == 2) && ((iYear % 4) != 0) && (iDay > 28)) {
347            iDay = 1;
348           }
349          // Set stored date based on current settings
350          //   If subsequently adjust the month so day is not valid
351          // then display   will advance to next valid date
352          currentDate = JulianDate(iDay, iMonth,   iYear);
353        }
354        break;
355      case SET_SPEED_ADJ:
356        //   increase or decrease correcton by 5 milliseconds
357        if (digitalRead(UP_BUTTON)   == LOW) {
358          speedCorrection += 5;
359        }
360        if (digitalRead(DOWN_BUTTON)   == LOW) {
361          speedCorrection -= 5;
362        }
363        break;
364     }
365  }
366}
367
368String FormatNumber(int value) {
369  // To add a leading   0 if required
370  if (value < 10) {
371    return "0" + String(value);
372  }
373   else {
374    return String(value);
375  }
376}
377
378void ShowTime(unsigned   long value) {
379  // Update display once a second
380  // or when rolls over midnight
381   if ((value > lastTime + 1000) || (value < lastTime)) {
382    lastTime = value;
383     unsigned long iHours;
384    unsigned long iMinutes;
385    unsigned long iSeconds;
386     SplitTime(value, iHours, iMinutes, iSeconds);
387
388    // Display the time   on line 0
389    lcd.setCursor(0, 0);
390    lcd.print("Time: " + FormatNumber(iHours)   + ":" +
391              FormatNumber(iMinutes) + ":" +
392              FormatNumber(iSeconds));
393   }
394}
395
396void ShowDate(float value) {
397  // Update display if date has   changed since
398  // the date was last displayed
399  if (lastDate != value) {
400     lastDate = value;
401    int iday;
402    int imonth;
403    int iyear;
404     String currentDay;
405    GregorianDate(value, iday, imonth, iyear);
406    int   dayOfWeek = (unsigned long)value % 7;
407    // Display the date on line 0
408    lcd.setCursor(0,   1);
409    lcd.print(dayArray[dayOfWeek]);
410    lcd.print(FormatNumber(iday) +   ":" +
411              FormatNumber(imonth) + ":" +
412              iyear);
413   }
414}
415
416void ShowDDMMSet(float value) {
417  int iday;
418  int imonth;
419   int iyear;
420  String currentDay;
421  GregorianDate(value, iday, imonth, iyear);
422   // Display day and month for adjusting
423  lcd.setCursor(0, 0);
424  lcd.print("Set   day & month:");
425  lcd.setCursor(0, 1);
426  lcd.print("Day:" + FormatNumber(iday)   + " Month:" +
427            FormatNumber(imonth));
428}
429
430
431void ShowYearSet(float   jd) {
432  int iday;
433  int imonth;
434  int iyear;
435  GregorianDate(jd, iday,   imonth, iyear);
436  // Display year for adjusting
437  lcd.setCursor(0, 0);
438   lcd.print("Set year:");
439  lcd.setCursor(0, 1);
440  lcd.print("Year: "   + FormatNumber(iyear));
441}
442
443void ShowTimeSet(unsigned long value) {
444   unsigned long iHours;
445  unsigned long iMinutes;
446  unsigned long iSeconds;
447   // Display time for adjusting
448  SplitTime(value, iHours, iMinutes, iSeconds);
449   lcd.setCursor(0, 0);
450  lcd.print("Set time:");
451  lcd.setCursor(0, 1);
452   lcd.print("Hours:" + FormatNumber(iHours) + " Mins:" +
453            FormatNumber(iMinutes));
454}
455
456void   ShowSpeedSet() {
457  // Display speed correction figure for adjusting
458  // could   be + or -
459  lcd.setCursor(0, 0);
460  lcd.print("Set speed adj:");
461  lcd.setCursor(0,   1);
462  lcd.print("Millis: ");
463  lcd.print(speedCorrection);
464  lcd.print("   ");
465}

1// Paul Brace Feb 2021
2// Script to accept millis() from Arduino
3//  and compare it to internal millis() to
4// assess inaccuracy of the Arduino clock.
5//  Assumes that the computer clock is accurate
6// -ve = Arduino is running slow  so enter as a +ve adjustment in the clock program
7// +ve = Arduino is running  fast so enter as a -ve adjustment to slow the clock down
8
9import processing.serial.*;
10
11Serial  theSerialPort;                   // create the serial port object
12
13int[] serialBytesArray  = new int[15];   // array to store incoming bytes
14int bytesCount = 0;                     //  current number of bytes received
15boolean init = false;                   // false  until handshake completed by receiving the character Z
16int fillColor = 255;                    //  defining the initial fill colour
17long mills = 0;                         // last  reading received
18long first = 0;                         // time of first mills  received so we can calculate the difference over an hour
19long now;                               //  number of millis elapsed since first mills received
20long firstReading = 100000;             // millis() in processing of first message received from Arduino
21long  DiffPerHour = 0;                   // the difference after the first hour has passed  
22int inByte;                             // last byte read
23
24void setup()  {
25  // define some canvas and drawing parameters
26  size(500, 500);
27  background(70);
28  noStroke();
29
30  // print the list of all serial devices so you know which  one to set for the Arduino
31  // will need to run program and edit if the correct  port is not set below
32  printArray(Serial.list());
33  // instantate the Serial  Communication
34  String thePortName = Serial.list()[1];
35  theSerialPort = new  Serial(this, thePortName, 9600);
36}
37void draw() {
38  // Display time settings
39  background(70);
40  fill(fillColor);
41  textSize(25);
42  text(hour() + ":"  + minute() + ":" + second(), 50, 50);
43  // the last read millis sent by the  Arduino
44  text("Incoming elapsed: " + mills, 50, 100);
45  // the current  elapsed since first read in Processing
46  text("Local elapsed: " + (now - firstReading),  50, 150);
47  // display the current difference
48  text("Diff: " + (mills -  (now - firstReading)), 50, 200);
49  // Check if 1 hour has passed and if the first  hour store the difference
50  if (((now - firstReading)>= 3600000) && (DiffPerHour  == 0)){
51    DiffPerHour = mills - (now - firstReading);
52  }
53  // Display  the first difference and the difference after the first hour
54  text("Diff after  1 hour: " + DiffPerHour, 50, 300);
55}
56
57void serialEvent(Serial myPort)  {
58  // read a byte from the serial port
59  inByte = myPort.read();
60  if  (init == false) {         // if not yet handshaked the see if handshake byte
61    if (inByte == 'Z') {       // if the byte read is Z
62      myPort.clear();          // clear the serial port buffer
63      init = true;             // store  the fact we had the first hello
64      myPort.write('Z');       // tell the Arduino  to send more
65      if (first == 0){
66        first = millis();
67      }
68    }
69  } 
70  else {                       
71    // if there already was  the first hello
72    // Add the latest byte from the serial port to array
73    if (inByte != 69) {        // Check not the end of message character E    
74      if (bytesCount < 14) {
75        serialBytesArray[bytesCount] = inByte;
76        bytesCount++;
77      }
78    }
79    if (inByte == 69) {
80      //  End of message
81      // store local time elapsed 
82      now  = millis();
83      // calculate incoming millis()
84      mills = 0;
85      for (int i = 1;  i <= bytesCount; i++) {
86        mills += (serialBytesArray[i - 1] - 48) * pow(10,  (bytesCount - i));
87      }
88      // Say we are ready to accept next message
89      // if this is the first reading then set the first difference 
90      if  (firstReading == 100000) {
91        firstReading = now;
92      }
93      myPort.write('Z');
94      // Reset bytesCount:
95      bytesCount = 0;
96    }
97  }
98}

1// Paul Brace Feb 2021
2// For use with corresponding Processing script
3//  to compare millis() from here to millis() in 
4// Processing using the computer  clock
5
6int inByte = 0;
7unsigned long firstReading = 100000;   // millis()  when first reading sent
8
9void setup() {
10  Serial.begin(9600);
11  // Send  the hello byte to Processing
12  sayHello();
13}
14
15void loop() {
16  //  if a byte is received on the serial port
17  // then read and discard it and send  current 
18  // value of millis()
19  if (Serial.available() > 0){
20    // get  incoming byte
21    inByte = Serial.read();
22    // send time elapsed since first  reading processing
23    Serial.print(millis() - firstReading);
24    Serial.print('E');
25    // repeat every 2 seconds
26    delay(2000);
27  }
28}
29
30void sayHello(){
31  // Wait until the serial port is available
32  // then send hello byte to start  handshake
33  while (Serial.available() <=0){
34    Serial.print('Z');                //  Send Z to processing to say Hello
35    delay(200);
36  }
37  firstReading =  millis();
38}

1// Paul Brace Feb 2021
2// Script to accept millis() from Arduino
3//
4  and compare it to internal millis() to
5// assess inaccuracy of the Arduino clock.
6//
7  Assumes that the computer clock is accurate
8// -ve = Arduino is running slow
9  so enter as a +ve adjustment in the clock program
10// +ve = Arduino is running
11  fast so enter as a -ve adjustment to slow the clock down
12
13import processing.serial.*;
14
15Serial
16  theSerialPort;                   // create the serial port object
17
18int[] serialBytesArray
19  = new int[15];   // array to store incoming bytes
20int bytesCount = 0;                     //
21  current number of bytes received
22boolean init = false;                   // false
23  until handshake completed by receiving the character Z
24int fillColor = 255;                    //
25  defining the initial fill colour
26long mills = 0;                         // last
27  reading received
28long first = 0;                         // time of first mills
29  received so we can calculate the difference over an hour
30long now;                               //
31  number of millis elapsed since first mills received
32long firstReading = 100000;
33             // millis() in processing of first message received from Arduino
34long
35  DiffPerHour = 0;                   // the difference after the first hour has passed
36  
37int inByte;                             // last byte read
38
39void setup()
40  {
41  // define some canvas and drawing parameters
42  size(500, 500);
43  background(70);
44
45  noStroke();
46
47  // print the list of all serial devices so you know which
48  one to set for the Arduino
49  // will need to run program and edit if the correct
50  port is not set below
51  printArray(Serial.list());
52  // instantate the Serial
53  Communication
54  String thePortName = Serial.list()[1];
55  theSerialPort = new
56  Serial(this, thePortName, 9600);
57}
58void draw() {
59  // Display time settings
60
61  background(70);
62  fill(fillColor);
63  textSize(25);
64  text(hour() + ":"
65  + minute() + ":" + second(), 50, 50);
66  // the last read millis sent by the
67  Arduino
68  text("Incoming elapsed: " + mills, 50, 100);
69  // the current
70  elapsed since first read in Processing
71  text("Local elapsed: " + (now - firstReading),
72  50, 150);
73  // display the current difference
74  text("Diff: " + (mills -
75  (now - firstReading)), 50, 200);
76  // Check if 1 hour has passed and if the first
77  hour store the difference
78  if (((now - firstReading)>= 3600000) && (DiffPerHour
79  == 0)){
80    DiffPerHour = mills - (now - firstReading);
81  }
82  // Display
83  the first difference and the difference after the first hour
84  text("Diff after
85  1 hour: " + DiffPerHour, 50, 300);
86}
87
88void serialEvent(Serial myPort)
89  {
90  // read a byte from the serial port
91  inByte = myPort.read();
92  if
93  (init == false) {         // if not yet handshaked the see if handshake byte
94
95    if (inByte == 'Z') {       // if the byte read is Z
96      myPort.clear();
97          // clear the serial port buffer
98      init = true;             // store
99  the fact we had the first hello
100      myPort.write('Z');       // tell the Arduino
101  to send more
102      if (first == 0){
103        first = millis();
104      }
105
106    }
107  } 
108  else {                       
109    // if there already was
110  the first hello
111    // Add the latest byte from the serial port to array
112
113    if (inByte != 69) {        // Check not the end of message character E    
114
115      if (bytesCount < 14) {
116        serialBytesArray[bytesCount] = inByte;
117
118        bytesCount++;
119      }
120    }
121    if (inByte == 69) {
122      //
123  End of message
124      // store local time elapsed 
125      now  = millis();
126
127      // calculate incoming millis()
128      mills = 0;
129      for (int i = 1;
130  i <= bytesCount; i++) {
131        mills += (serialBytesArray[i - 1] - 48) * pow(10,
132  (bytesCount - i));
133      }
134      // Say we are ready to accept next message
135
136      // if this is the first reading then set the first difference 
137      if
138  (firstReading == 100000) {
139        firstReading = now;
140      }
141      myPort.write('Z');
142
143      // Reset bytesCount:
144      bytesCount = 0;
145    }
146  }
147}

1// Paul Brace - Feb 2021
2// Simple Clock with Date created just using  a Arduino - no RTC module
3// Program incorporates a time correction adjustment  to compensate for the internal
4// clock speed not being 100% accurate.
5//  Once correct speed adjustment set the clock is surprisingly accurate.
6// In my  test it did not lose or gain any time over a 5 day period.
7// Displays time on  a 16x2 LCD display
8// Buttons to set time
9//   Mode button (pin 2) toggles  set time, set date and run
10//   Button 1 (pin 3) Increments Minutes and Month  and decreases Year/speed adj
11//   Button 2 (pin 4) Increments Hour and Day and  increases Year./speed adj
12// 24 Hour display
13
14// Include the library driver  for display:
15#include <LiquidCrystal.h>
16
17// LiquidCrystal lcd( RS, EN,  D4,D5, D6, D7)
18LiquidCrystal lcd(12, 13, 6, 7, 8, 9); // create an lcd object  and assign the pins
19
20// Define buttons and buzzer connections
21#define MODE_BUTTON  2
22#define HOUR_BUTTON 3                  // Same button different definitions  to
23#define UP_BUTTON 3                    // make code easier to understand 
24#define  DAY_BUTTON 3
25#define MINUTE_BUTTON 4                // Same button different  definitions to
26#define DOWN_BUTTON 4                  // make code easier to  understand 
27#define MONTH_BUTTON 4
28
29// Current mode settings
30#define  SHOW_TIME 1                    // 1 = running - show time
31#define SET_TIME  2                    // 2 = time set
32#define SET_YEAR  3                    //  3 = year set
33#define SET_DATE  4                    // 4 = day/month set 
34#define  SET_SPEED_ADJ  5               // 5 = amend the speedCorrection variable
35
36int  speedCorrection = 3545;            // Number of milliseconds my Nano clock runs  slow per hour
37// negative number here if it is running fast
38// change to match  your Arduino
39
40// Volatile variables as changed in an interrupt and we
41//  need to force the system to read the actual variable
42// when used outside the  interrupt and not use a cached version
43volatile unsigned long currentTime;    //  Duration in milliseconds from midnight
44unsigned long lastTime = -1000;        //  lastTime that ShowTime was called initialised to -1000 so shows immediately
45volatile  unsigned long elapsed;        // Timer used for delay and hour count
46
47unsigned  long millisecondsInADay;      // Milliseconds in 24 hours
48unsigned long millisecondsInHour;      // Milliseconds in 1 hour
49int currentMode;                       // 1 =  running - show time
50// 2 = time set
51// 3 = year set
52// 4 = day/month set
53
54float  currentDate;                     // Julian date
55float lastDate = 0.0;                  //  last date that ShowDate was called
56int currentDay;
57int currentMonth;
58int  currentYear;
59
60char *dayArray[] = {  "Tue.  ",       // Will show a compiler  warning but works fine
61                      "Wed.  ",
62                      "Thur.  ",
63                      "Fri.  ",
64                      "Sat.  ",
65                      "Sun.  ",
66                      "Mon.  "
67                   };
68
69void  setup() {
70  // Set up  time interrupt - millis() rolls over after 50 days so
71  // we are using our own millisecond counter which we can reset at
72  // the  end of each day
73  TCCR0A = (1 << WGM01);      //Set the CTC mode Compare time  and trigger interrupt
74  OCR0A = 0xF9;               //Set value for time to compare  to ORC0A for 1ms = 249  (8 bits so max is 256)
75  //[(Clock speed/Prescaler value)*Time  in seconds] - 1
76  //[(16,000,000/64) * .001] - 1 = 249 = 1 millisecond
77  TIMSK0  |= (1 << OCIE0A);    //set timer compare interrupt
78  TCCR0B |= (1 << CS01);      //Set  the prescale 1/64 clock
79  TCCR0B |= (1 << CS00);      // ie 110 for last 3 bits
80  TCNT0  = 0;                 //initialize counter value to 0
81  sei();                      //Enable  interrupt
82
83  pinMode(MINUTE_BUTTON, INPUT_PULLUP);
84  pinMode(HOUR_BUTTON,  INPUT_PULLUP);
85  pinMode(MODE_BUTTON, INPUT_PULLUP);
86  //pinMode(BUZZER, OUTPUT);
87  currentTime = 0;                          // Set to current time to mindnight
88  currentDate = JulianDate(1, 1, 2021);     // Set base date
89  elapsed = 0;                              //  Set period counter to 0
90  millisecondsInADay = 24ul * 60 * 60 * 1000;
91  millisecondsInHour  = 60ul * 60 * 1000;
92  currentMode = SHOW_TIME;                  // Initial mode  is running and showing time and date
93  // Setup LCD
94  lcd.begin(16, 2);
95  lcd.noAutoscroll();
96  lcd.display();
97  lcd.clear();
98  ShowTime(currentTime);
99}
100
101void  loop() {
102  // loop runs every 150 milliseconds
103
104  // If at end of the day  reset time and increase date
105  if ((currentMode == SHOW_TIME) &&
106      (currentTime  > millisecondsInADay)) {
107    //Next day
108    // Stop interrupts while reset  time
109    noInterrupts();
110    currentTime -= millisecondsInADay;
111    interrupts();
112    currentDate++;
113  }
114  // At the end of each hour adjust the elapsed time  for
115  // the inacuracy in the Arduino clock
116  if (elapsed >= millisecondsInHour)  {
117    noInterrupts();
118    // Adjust time for slow/fast running Arduino clock
119    currentTime += speedCorrection;
120    // Reset to count the next hour
121    elapsed  = 0;
122    interrupts();
123  }
124
125  // Check if any buttons have been pressed
126  CheckButtons();
127
128  // Show display based on current mode
129  switch (currentMode)  {
130    case SHOW_TIME:
131      // Display current time and date
132      ShowTime(currentTime);
133      ShowDate(currentDate);
134      break;
135    case SET_TIME:
136      // Display  screen for setting the time
137      ShowTimeSet(currentTime);
138      break;
139    case SET_YEAR:
140      // Display screen for setting the year
141      ShowYearSet(currentDate);
142      break;
143    case SET_DATE:
144      // Display screen for setting the day  and month
145      ShowDDMMSet(currentDate);
146      break;
147    case SET_SPEED_ADJ:
148      // Display screen for adjusting the speed correction
149      ShowSpeedSet();
150      break;
151  }
152  Wait(150);
153}
154
155// This is interrupt is called when  the compare time has been reached
156// hence will be called once a millisecond  based on the
157// OCR0A register setting.
158ISR(TIMER0_COMPA_vect) {
159  if (currentMode  != SET_TIME)
160    currentTime++;
161  elapsed++;
162}
163
164float JulianDate(int  iday, int imonth, int iyear) {
165  // Calculate julian date (tested up to the year  20,000)
166  unsigned long d = iday;
167  unsigned long m = imonth;
168  unsigned  long y = iyear;
169  if (m < 3) {
170    m = m + 12;
171    y = y - 1;
172  }
173  unsigned long t1 = (153 * m - 457) / 5;
174  unsigned long t2 = 365 * y + (y /  4) - (y / 100) + (y / 400);
175  return 1721118.5 + d + t1 + t2;
176}
177
178void  GregorianDate(float jd, int &iday, int &imonth, int &iyear) {
179  // Note 2100  is the next skipped leap year - compensates for skipped leap years
180  unsigned  long f = jd + 68569.5;
181  unsigned long e = (4.0 * f) / 146097;
182  unsigned  long g = f - (146097 * e + 3) / 4;
183  unsigned long h = 4000ul * (g + 1) / 1461001;
184  unsigned long t = g - (1461 * h / 4) + 31;
185  unsigned long u = (80ul * t) /  2447;
186  unsigned long v = u / 11;
187  iyear = 100 * (e - 49) + h + v;
188  imonth  = u + 2 - 12 * v;
189  iday = t - 2447 * u / 80;
190}
191
192void SplitTime(unsigned  long curr, unsigned long &ulHour,
193               unsigned long &ulMin, unsigned  long &ulSec) {
194  // Calculate HH:MM:SS from millisecond count
195  ulSec = curr  / 1000;
196  ulMin = ulSec / 60;
197  ulHour = ulMin / 60;
198  ulMin -= ulHour  * 60;
199  ulSec = ulSec - ulMin * 60 - ulHour * 3600;
200}
201
202unsigned long  SetTime(unsigned long ulHour, unsigned long ulMin,
203                      unsigned  long ulSec) {
204  // Sets the number of milliseconds from midnight to current time
205  return (ulHour * 60 * 60 * 1000) +
206         (ulMin * 60 * 1000) +
207         (ulSec  * 1000);
208}
209
210void Wait(unsigned long value) {
211  // Create our own dealy  function
212  // We have set our own interrupt on TCCR0A
213  // hence millis()  and delay() will no longer work
214  unsigned long startTime = elapsed;
215  while  ((elapsed - startTime) < value) {
216    // Just wait
217  }
218}
219
220void CheckButtons()  {
221  // If the mode button has been pressed pin will go LOW
222  if (digitalRead(MODE_BUTTON)  == LOW) {
223    // Advance to next mode
224    switch (currentMode) {
225      case  SHOW_TIME:
226        currentMode = SET_TIME;
227        lcd.clear();
228        break;
229      case SET_TIME:
230        currentMode = SET_YEAR;
231        lcd.clear();
232        break;
233      case SET_YEAR:
234        currentMode = SET_DATE;
235        lcd.clear();
236        break;
237      case SET_DATE:
238        currentMode = SET_SPEED_ADJ;
239        lcd.clear();
240        break;
241      case SET_SPEED_ADJ:
242        currentMode  = SHOW_TIME;
243        lcd.clear();
244        // Reset variables so that the display  will be forced to update
245        // the next time ShowTime and ShowDate are called
246        lastTime = 0;
247        lastDate = 0.0;
248        break;
249    }
250  }
251  if (currentMode != SHOW_TIME) {
252    switch (currentMode) {
253      //  If mode anyhting other than SHOW_TIME check buttons
254      // Pin goes LOW when  ssociated button pressed
255      case SET_TIME:
256        if (digitalRead(MINUTE_BUTTON)  == LOW) {
257          // Advance minute
258          unsigned long iHours;
259          unsigned long iMinutes;
260          unsigned long iSeconds;
261          SplitTime(currentTime,  iHours, iMinutes, iSeconds);
262          if (iMinutes < 59) {
263            iMinutes++;
264          }
265          else {
266            iMinutes = 0;
267          }
268          // Set stored milliseconds based on current setting
269          noInterrupts();
270          currentTime = SetTime(iHours, iMinutes, 0);
271          elapsed = 0;
272          interrupts();
273        }
274        if (digitalRead(HOUR_BUTTON) ==  LOW) {
275          // Advance hour
276          unsigned long iHours;
277          unsigned  long iMinutes;
278          unsigned long iSeconds;
279          SplitTime(currentTime,  iHours, iMinutes, iSeconds);
280          if (iHours < 23) {
281            iHours++;
282          }
283          else {
284            iHours = 0;
285          }
286          //  Set stored milliseconds based on current setting
287          noInterrupts();
288          currentTime = SetTime(iHours, iMinutes, 0);
289          elapsed = 0;
290          interrupts();
291        }
292        break;
293      case SET_YEAR:
294        if (digitalRead(UP_BUTTON) == LOW) {
295          // Increase year
296          int  iDay;
297          int iMonth;
298          int iYear;
299          GregorianDate(currentDate,  iDay, iMonth, iYear);
300          iYear++;
301          // Set stored date based  on current settings
302          currentDate = JulianDate(iDay, iMonth, iYear);
303        }
304        if (digitalRead(DOWN_BUTTON) == LOW) {
305          // Decrease  year
306          int iDay;
307          int iMonth;
308          int iYear;
309          GregorianDate(currentDate, iDay, iMonth, iYear);
310          iYear--;
311          // Set stored date based on current settings
312          currentDate  = JulianDate(iDay, iMonth, iYear);
313        }
314        break;
315      case  SET_DATE:
316        if (digitalRead(MONTH_BUTTON) == LOW) {
317          // Advance  month
318          int iDay;
319          int iMonth;
320          int iYear;
321          GregorianDate(currentDate, iDay, iMonth, iYear);
322          iMonth++;
323          if (iMonth > 12) {
324            iMonth = 1;
325          }
326          //  Set stored date based on current settings
327          currentDate = JulianDate(iDay,  iMonth, iYear);
328        }
329        if (digitalRead(DAY_BUTTON) == LOW) {
330          // Advance day
331          int iDay;
332          int iMonth;
333          int  iYear;
334          GregorianDate(currentDate, iDay, iMonth, iYear);
335          iDay++;
336          if (iDay > 31) {
337            iDay = 1;
338          }
339          if  (((iMonth == 4) || (iMonth == 6) || (iMonth == 9) || (iMonth == 11))
340              &&  (iDay > 30)) {
341            iDay = 1;
342          }
343          if ((iMonth  == 2) && (iDay > 29)) {
344            iDay = 1;
345          }
346          if  ((iMonth == 2) && ((iYear % 4) != 0) && (iDay > 28)) {
347            iDay = 1;
348          }
349          // Set stored date based on current settings
350          //  If subsequently adjust the month so day is not valid
351          // then display  will advance to next valid date
352          currentDate = JulianDate(iDay, iMonth,  iYear);
353        }
354        break;
355      case SET_SPEED_ADJ:
356        //  increase or decrease correcton by 5 milliseconds
357        if (digitalRead(UP_BUTTON)  == LOW) {
358          speedCorrection += 5;
359        }
360        if (digitalRead(DOWN_BUTTON)  == LOW) {
361          speedCorrection -= 5;
362        }
363        break;
364    }
365  }
366}
367
368String FormatNumber(int value) {
369  // To add a leading  0 if required
370  if (value < 10) {
371    return "0" + String(value);
372  }
373  else {
374    return String(value);
375  }
376}
377
378void ShowTime(unsigned  long value) {
379  // Update display once a second
380  // or when rolls over midnight
381  if ((value > lastTime + 1000) || (value < lastTime)) {
382    lastTime = value;
383    unsigned long iHours;
384    unsigned long iMinutes;
385    unsigned long iSeconds;
386    SplitTime(value, iHours, iMinutes, iSeconds);
387
388    // Display the time  on line 0
389    lcd.setCursor(0, 0);
390    lcd.print("Time: " + FormatNumber(iHours)  + ":" +
391              FormatNumber(iMinutes) + ":" +
392              FormatNumber(iSeconds));
393  }
394}
395
396void ShowDate(float value) {
397  // Update display if date has  changed since
398  // the date was last displayed
399  if (lastDate != value) {
400    lastDate = value;
401    int iday;
402    int imonth;
403    int iyear;
404    String currentDay;
405    GregorianDate(value, iday, imonth, iyear);
406    int  dayOfWeek = (unsigned long)value % 7;
407    // Display the date on line 0
408    lcd.setCursor(0,  1);
409    lcd.print(dayArray[dayOfWeek]);
410    lcd.print(FormatNumber(iday) +  ":" +
411              FormatNumber(imonth) + ":" +
412              iyear);
413  }
414}
415
416void ShowDDMMSet(float value) {
417  int iday;
418  int imonth;
419  int iyear;
420  String currentDay;
421  GregorianDate(value, iday, imonth, iyear);
422  // Display day and month for adjusting
423  lcd.setCursor(0, 0);
424  lcd.print("Set  day & month:");
425  lcd.setCursor(0, 1);
426  lcd.print("Day:" + FormatNumber(iday)  + " Month:" +
427            FormatNumber(imonth));
428}
429
430
431void ShowYearSet(float  jd) {
432  int iday;
433  int imonth;
434  int iyear;
435  GregorianDate(jd, iday,  imonth, iyear);
436  // Display year for adjusting
437  lcd.setCursor(0, 0);
438  lcd.print("Set year:");
439  lcd.setCursor(0, 1);
440  lcd.print("Year: "  + FormatNumber(iyear));
441}
442
443void ShowTimeSet(unsigned long value) {
444  unsigned long iHours;
445  unsigned long iMinutes;
446  unsigned long iSeconds;
447  // Display time for adjusting
448  SplitTime(value, iHours, iMinutes, iSeconds);
449  lcd.setCursor(0, 0);
450  lcd.print("Set time:");
451  lcd.setCursor(0, 1);
452  lcd.print("Hours:" + FormatNumber(iHours) + " Mins:" +
453            FormatNumber(iMinutes));
454}
455
456void  ShowSpeedSet() {
457  // Display speed correction figure for adjusting
458  // could  be + or -
459  lcd.setCursor(0, 0);
460  lcd.print("Set speed adj:");
461  lcd.setCursor(0,  1);
462  lcd.print("Millis: ");
463  lcd.print(speedCorrection);
464  lcd.print("  ");
465}

1// Paul Brace Feb 2021
2// For use with corresponding Processing script
3//
4  to compare millis() from here to millis() in 
5// Processing using the computer
6  clock
7
8int inByte = 0;
9unsigned long firstReading = 100000;   // millis()
10  when first reading sent
11
12void setup() {
13  Serial.begin(9600);
14  // Send
15  the hello byte to Processing
16  sayHello();
17}
18
19void loop() {
20  //
21  if a byte is received on the serial port
22  // then read and discard it and send
23  current 
24  // value of millis()
25  if (Serial.available() > 0){
26    // get
27  incoming byte
28    inByte = Serial.read();
29    // send time elapsed since first
30  reading processing
31    Serial.print(millis() - firstReading);
32    Serial.print('E');
33
34    // repeat every 2 seconds
35    delay(2000);
36  }
37}
38
39void sayHello(){
40
41  // Wait until the serial port is available
42  // then send hello byte to start
43  handshake
44  while (Serial.available() <=0){
45    Serial.print('Z');                //
46  Send Z to processing to say Hello
47    delay(200);
48  }
49  firstReading =
50  millis();
51}