#include <TimeLib.h>
#include <Wire.h>
#include <DS1307RTC.h>  // a basic DS1307 library that returns time as a time_t

#define PIN_SCE   7
#define PIN_RESET 6
#define PIN_DC    5
#define PIN_SDIN  11
#define PIN_SCLK  13

#define LCD_COMMAND    LOW
#define LCD_DATA     HIGH

#define LCD_X     84
#define LCD_Y     48

String now_time;
char printTime;

void gotoXY(int x, int y) {
  LCDWrite(0, 0x80 | x);  // Column.
  LCDWrite(0, 0x40 | y);  // Row.  ?

//This takes a large array of bits and sends them to the LCD
void LCDBitmap(char my_array[]){
  for (int index = 0 ; index < (LCD_X * LCD_Y / 8) ; index++)
    LCDWrite(LCD_DATA, my_array[index]);

//This function takes in a character, looks it up in the font table/array
//And writes it to the screen
//Each character is 8 bits tall and 5 bits wide. We pad one blank column of
//pixels on each side of the character for readability.
void LCDCharacter(char character) {
  LCDWrite(LCD_DATA, 0x00); //Blank vertical line padding

  for (int index = 0 ; index < 5 ; index++)
    LCDWrite(LCD_DATA, ASCII[character - 0x20][index]);
    //0x20 is the ASCII character for Space (' '). The font table starts with this character

  LCDWrite(LCD_DATA, 0x00); //Blank vertical line padding

//Given a string of characters, one by one is passed to the LCD
void LCDString(char *characters) {
  while (*characters)

//Clears the LCD by writing zeros to the entire screen
void LCDClear(void) {
  for (int index = 0 ; index < (LCD_X * LCD_Y / 8) ; index++)
    LCDWrite(LCD_DATA, 0x00);

  gotoXY(0, 0); //After we clear the display, return to the home position

//This sends the magical commands to the PCD8544
void LCDInit(void) {

  //Configure control pins
  pinMode(PIN_SCE, OUTPUT);
  pinMode(PIN_DC, OUTPUT);
  pinMode(PIN_SDIN, OUTPUT);
  pinMode(PIN_SCLK, OUTPUT);

  //Reset the LCD to a known state
  digitalWrite(PIN_RESET, LOW);
  digitalWrite(PIN_RESET, HIGH);

  LCDWrite(LCD_COMMAND, 0x21); //Tell LCD that extended commands follow
  LCDWrite(LCD_COMMAND, 0xAF); //Set LCD Vop (Contrast): Try 0xB1(good @ 3.3V) or 0xBF if your display is too dark
  LCDWrite(LCD_COMMAND, 0x04); //Set Temp coefficent
  LCDWrite(LCD_COMMAND, 0x14); //LCD bias mode 1:48: Try 0x13 or 0x14

  LCDWrite(LCD_COMMAND, 0x20); //We must send 0x20 before modifying the display control mode
  LCDWrite(LCD_COMMAND, 0x0C); //Set display control, normal mode. 0x0D for inverse

//There are two memory banks in the LCD, data/RAM and commands. This 
//function sets the DC pin high or low depending, and then sends
//the data byte
void LCDWrite(byte data_or_command, byte data) {
  digitalWrite(PIN_DC, data_or_command); //Tell the LCD that we are writing either to data or a command

  //Send the data
  digitalWrite(PIN_SCE, LOW);
  shiftOut(PIN_SDIN, PIN_SCLK, MSBFIRST, data);
  digitalWrite(PIN_SCE, HIGH);

void setup(void) {
   while (!Serial) ; // Needed for Leonardo only
   setSyncProvider(RTC.get);   // the function to get the time from the RTC
   if (timeStatus() != timeSet) 
     Serial.println("Unable to sync with the RTC");
     Serial.println("RTC has set the system time");

void loop(void) {
  if(timeStatus() == timeSet)
void digitalClockDisplay(){
  // digital clock display of the time
  if(minute() < 10)
    now_time = String(hour()) + ":0" + String(minute());
  else if(minute() >= 10){
    now_time = String(hour()) + ":" + String(minute());
   LCDString("Time: ");
   for(int i = 0; i <= now_time.length()-1; i++)
      printTime = now_time.charAt(i);


void printDigits(int digits){
  // utility function for digital clock display: prints preceding colon and leading 0
  if(digits < 10)

When I run the code the time will display perfectly on the Serial Monitor but when I connect it to my Nokia LCD screen the words "Time: " will appear along with some random characters. Anyone know why this is?

  • LCDString expects a c-string not a single character.
    – gre_gor
    Feb 17, 2017 at 15:11

1 Answer 1


I assume you are writing now_time one Char at a time because the LCD library does not accept the String object as input? LCDString assumes you will pass a C-style string -- that is a pointer to an array of char. When you pass in one character, it's not a pointer to a C-style string, but the LCDString function is assuming that it's a pointer to some bit of memory elsewhere.

Try not sending one Char at a time, but:


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