Heeya Guys! Today I created a project with the help of instructables site. I followed the on screen steps and everything. Uploaded the sketch and it works like a charm, but there's one problem.

Everything works correctly but not the "Day", i.e as of today its Friday, 9 April 2021, the clock shows the correct time and date but it tells that today is "Tuesday" in place of Friday. I don't know why this is happening. Any help would be appreciated :) Here's the code that I'm using:

/*Arduino Clock by AnthoTRONICS
* Last edit: March 22,2019
// Libraries you'll need (Same as the ones in the guide:

// MD Parola 3.0.1: https://github.com/MajicDesigns/MD_Parola // click the link to download the library
// MD_MAX72XX 3.0.2: https://github.com/MajicDesigns/MD_MAX72XX //click the link to download the library
// DS3231 1.0.2: https://github.com/NorthernWidget/DS3231 // click the link to download

// Header file includes
// These are for the matrix
#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <SPI.h>
#include "Font_Data.h"

//These are for the clock
#include <DS3231.h>
#include <Wire.h>
DS3231 Clock;

bool Century=false;
bool h12;
bool PM;
byte  dd,mm,yyy;
uint16_t  h, m, s;

#define MAX_DEVICES 4 // Set the number of devices
// NOTE: These pin numbers will probably not work with your hardware and may
// need to be adapted
#define CLK_PIN   13
#define DATA_PIN  11
#define CS_PIN    10

// Hardware SPI connection

#define SPEED_TIME 75 // speed of the transition
#define PAUSE_TIME  0  

#define MAX_MESG  20

// Global variables
char szTime[9];    // mm:ss\0
char szMesg[MAX_MESG+1] = "";

uint8_t degC[] = { 6, 3, 3, 56, 68, 68, 68 }; // Deg C
uint8_t degF[] = { 6, 3, 3, 124, 20, 20, 4 }; // Deg F

char *mon2str(uint8_t mon, char *psz, uint8_t len)

// Get a label from PROGMEM into a char array
  static const __FlashStringHelper* str[] =
    F("Jan"), F("Feb"), F("Mar"), F("Apr"),
    F("May"), F("Jun"), F("Jul"), F("Aug"),
    F("Sep"), F("Oct"), F("Nov"), F("Dec")

  strncpy_P(psz, (const char PROGMEM *)str[mon-1], len);
  psz[len] = '\0';


char *dow2str(uint8_t code, char *psz, uint8_t len)
  static const __FlashStringHelper*  str[] =
  F("Sunday"), F("Monday"), F("Tuesday"),
  F("Wednesday"), F("Thursday"), F("Friday"),
  F("Saturday"), F("Sunday")

  strncpy_P(psz, (const char PROGMEM *)str[code-1], len);
  psz[len] = '\0';

// Time Setup: Code for reading clock time
void getTime(char *psz, bool f = true)
  s = Clock.getSecond();
  m = Clock.getMinute();
  h =Clock.getHour(h12,PM); //24hr Format
  sprintf(psz, "%02d%c%02d", h, (f ? ':' : ' '), m);
  //12hr Format
  //uncomment if you want the clock to be in 12hr Format
  /*if (Clock.getHour(h12,PM)>=13 || Clock.getHour(h12,PM)==0)
    h = Clock.getHour(h12,PM) - 12;
    h = Clock.getHour(h12,PM);

void getDate(char *psz)
// Date Setup: Code for reading clock date
   char  szBuf[10];
   mm=Clock.getMonth(Century); //12
   sprintf(psz, "%d %s %04d",dd , mon2str(mm, szBuf, sizeof(szBuf)-1),(yyy + 2000));
 //strcpy(szMesg, "29 Feb 2016");

void setup(void)
  P.setInvert(false); //we don't want to invert anything so it is set to false
  P.setZone(0,  MAX_DEVICES-4, MAX_DEVICES-1);
  P.setZone(1, MAX_DEVICES-4, MAX_DEVICES-1);

  P.displayZoneText(0, szMesg, PA_CENTER, SPEED_TIME, 0,PA_PRINT , PA_NO_EFFECT);

  P.addChar('$', degC);
  P.addChar('&', degF);


void loop(void)
  static uint32_t lastTime = 0; // millis() memory
  static uint8_t  display = 0;  // current display mode
  static bool flasher = false;  // seconds passing flasher


   if (P.getZoneStatus(0))
    switch (display)
      case 0:    // Temperature deg C
      //P.setTextEffect(0, PA_SCROLL_LEFT, PA_SCROLL_UP);
      P.setTextEffect(0, PA_MESH, PA_BLINDS);
      dtostrf(Clock.getTemperature(), 3, 1, szMesg);
      strcat(szMesg, "$");
      //strcat(szMesg, "26.5$");


      case 1: // Temperature deg F
        //P.setTextEffect(0, PA_SCROLL_UP, PA_SCROLL_LEFT);
        P.setTextEffect(0, PA_OPENING, PA_GROW_DOWN);
        dtostrf((1.8 *Clock.getTemperature() )+32, 3, 1, szMesg);
        strcat(szMesg, "&");
   // strcpy(szMesg, "71.6&");


      case 2: // Clock
     P.setFont(0, numeric7Seg);
     P.setTextEffect(0, PA_PRINT, PA_NO_EFFECT);
     //Sleep Mode
     //Uncomment to enable Sleep Mode and adjust the hours to your needs
     /*if (h==12 || h<8)//Time intervals (in this case, from 12AM to 8AM) 
      P.setIntensity(0); //Set display brightness to lowest setting
      P.setIntensity(6); //Set display brightness to 6 (15 is the brighest)

     if (millis() - lastTime >= 1000)
    lastTime = millis();
    getTime(szMesg, flasher);
    flasher = !flasher;
    if(s==00&& s<=30){
    P.setTextEffect(0, PA_PRINT, PA_SCROLL_UP);

    //  strcpy(szMesg, "36 % RH");               
      case 3: // day of week
        P.setTextEffect(0, PA_SCROLL_LEFT, PA_SCROLL_LEFT);
        dow2str(Clock.getDoW()+1, szMesg, MAX_MESG); // Added +1 to get correct DoW

       //dow2str(5, szMesg, MAX_MESG);
      default:  // Calendar
        P.setTextEffect(0, PA_SCROLL_LEFT, PA_SCROLL_LEFT);
        display = 0;


  • If your problem isn't dependent on it, remove your display code and more people will be able to compile your example.
    – timemage
    Apr 9, 2021 at 13:23
  • 1
    Did you set the correct day of the week? The clock can't work it out from the date, it needs to be told it.
    – Majenko
    Apr 9, 2021 at 13:31
  • Note that, unlike the DS3231 library, RTClib computes the day of the week from the other date fields. Apr 9, 2021 at 13:43
  • put in a bunch of serial.print commands to determine what are the variable values at different points in the program flow
    – jsotola
    Apr 9, 2021 at 15:48
  • Re-read @Majenko's comment-- You need to set the correct DOW in the DS3231 when you set its time. The DS3231 does not reset the rolling DOW register when you reset the other registers. If it is uninitialized, the results are indeterminate. github.com/NorthernWidget/DS3231/blob/master/DS3231.cpp#L274
    – Dave X
    Sep 6, 2021 at 17:57

2 Answers 2


The library seems to be addressing device register 3. According to the DS3231 datasheet this register has valid values 1-7, with 1 being Sunday.

You have:

dow2str(Clock.getDoW()+1, szMesg, MAX_MESG);

1-7 becomes 2-8. And then, how dow2str:

strncpy_P(psz, (const char PROGMEM *)str[code-1], len);

2-8, become array indices 1-7.

Your array is:

  static const __FlashStringHelper*  str[] =
  F("Sunday"), F("Monday"), F("Tuesday"),
  F("Wednesday"), F("Thursday"), F("Friday"),
  F("Saturday"), F("Sunday")

The indices here start at 0, so everything is off-by-one. But, I don't know how you get Tuesday out of Friday. If you cut your code down to something smaller that is testable without the display code, just using Serial, you'll probably get better answers.

  • It is probably an initialization problem. The DS3231 doesn't recompute the DOW when the other registers are set, so if the other registers are properly set but the register 3 DOW is wrong, it likely wasn't properly initialized with the rest.
    – Dave X
    Sep 6, 2021 at 18:00

I did this project and my weekday was off by 1, always a day earlier I fixed this by removing the Sunday at the beginning of the list and moving it to the end why you had two Sunday entries I do not know. That fixed my issue. I do not know why yours is showing Tuesday for Friday though.

char *dow2str(uint8_t code, char psz, uint8_t len) { static const __FlashStringHelper str[] = { F("Monday"), F("Tuesday"), F("Wednesday"), F("Thursday"), F("Friday"), F("Saturday"),F("Sunday") }

  • Not an answer...
    – VE7JRO
    Dec 13, 2022 at 1:48

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