Formatting on a 20x4 LCD

Projects Programming
1

Folks,

I'm working on code for a possible project for my sister in law. She likes to keep track of birthdays. So I wanted to build her a clock which displays a simple happy birthday message along with the name of the family member on the day of the persons birthday (from midnight to midnight). On days when there isn't a birthday, I want to display the temperature and humidity. However when testing the code I noticed trailing characters when switching between the happy birthday message and the temp and humidity due to the different lengths of the text. How would I go about dealing with this?

#include <Wire.h>                                 // include wire library
#include <RTClib.h>                               // RTC
#include <LiquidCrystal_I2C.h>                    // for LCD
#include "DHT_U.h"
#define Type DHT22

LiquidCrystal_I2C lcd(0x27, 20, 4);               // create LCD, address is 0x27
RTC_DS3231 rtc;                                   // create rtc, address is 0x68

DHT DHTT(sensePin, Type);
int sensePin=7;

float humidity;
float tempC;
float tempF;

// 0=Sunday, 1=Monday,...6=Saturday
const char dayInWords[7][4] = {"SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT"};    

// 0=" ", 1=Jan, 2=Feb, ... 12=Dec
const char monthInWords[13][4] = {" ", "JAN", "FEB", "MAR", "APR", "MAY", "JUN", 
                                         "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"};
                                         
void setup()
{
  Serial.begin(9600);                             // start serial monitor for debugging if needed

  lcd.init();                                     // initialize LCD
  lcd.backlight();                                // turn on LCD backlight
    
  rtc.begin();                                    // initialize RTC

  DHTT.begin();

} //END of setup()


void loop()
{
  DateTime rtcTime = rtc.now();                   // get time

  int ss = rtcTime.second();                      // save seconds
  int mm = rtcTime.minute();                      // save minutes
  int hh = rtcTime.twelveHour();                  // etc.
  int DD = rtcTime.dayOfTheWeek();
  int dd = rtcTime.day();
  int MM = rtcTime.month();
  int yyyy = rtcTime.year();                      // save year

  lcd.setCursor(0,0);                             // Set cursor to top left position

  lcd.print(monthInWords[MM]);                    // print date in MMM-dd-yyyy format
  lcd.print("-");                                 // print "-" for formating
  if (dd<10) lcd.print ("0");                     // add 0 before hour if less than 10
  lcd.print(dd);                                  // print day
  lcd.print("-");                                 // print "-" for formatting
  lcd.print(yyyy);                                // print year
  lcd.print("  ");                                // print space for formatting
  lcd.print(dayInWords[DD]);                       // print day in DDD format
  
  lcd.setCursor(0,1);                             // set cursor at beginning of next row

  if (hh<10) lcd.print("0");                      // add 0 before hour if less than 10
  lcd.print(hh);                                  // print hour
  lcd.print(":");                                 // add ":" for formatting
  if (mm<10) lcd.print("0");                      // add 0 before minite if less than 10
  lcd.print(mm);                                  // print minutes
  lcd.print(":");                                 // add ":" for formatting
  if (ss<10) lcd.print("0");                      // add 0 before seconds if less than 10
  lcd.print(ss);                                  // print seconds
  if (rtcTime.isPM()) lcd.print(" PM");           // print PM if PM
  else lcd.print (" AM");                         // else print AM
  
  humidity = DHTT.readHumidity();
  tempC = DHTT.readTemperature();
  tempF = DHTT.readTemperature(true);

  if (MM == 1 && dd == 6 && hh == 7 && mm == 16) 
  {
    lcd.setCursor(0,2);
    lcd.print("Happy Birthday");
    lcd.setCursor(0,3);
    lcd.print("Harry Wagner");
  }
  else {
    lcd.setCursor(0,2);
    lcd.print("Temperature: ");
    lcd.print(tempF);
    lcd.setCursor(0,3);
    lcd.print("Humidity: ");
    lcd.print(humidity);
  }
  

}

Best,

Tony

2

The easiest way,

clear the LCD screen before writing a new message

There should be a function called lcd.clear() or something. Take note though, this will literally empty everything on the screen and your cursor will start at 0,0

3

It flickers horribly when I use lcd.clear(). I think I'm clearing and writing constantly. I was hoping there was a relatively simple strategy but I don't see it.

4

That is correct. Does the information that needs to be displayed change that fast? You can slow it down by adding delay at the end

5

Clear the display when going between the birthday message and the temperature/humidity message.
Once you are on the temperature/humidity message, only update the data itself, and then only when it changes. No need to clear the display for that, just overwrite the previous data.

6

Some hints on using the display.

Never use clear() in loop() code.

There is no reason to update a display more often than about 2 times a second. Use millis timing to do updates, not delay().
Several things at a time.
Beginner's guide to millis().
Blink without delay().

Only update the display when the data changes.

Write constant length data to the display. For instance with a 20 character display write 20 characters even if you have to pad with spaces.

lcd.setcursor(0,0);
lcd.print("Happy B'day         ");  // overwrite old data with spaces

Or
Clear the space that you will write to with spaces, use setCursor to reset the cursor and write your data.

lcd.setcursor(0,0);
lcd.print("                    ");  // overwrite old data with spaces
lcd.setcursor(0,0);
lcd.print("Happy B'day");
7

Thanks all. Karma sent.

@groundFungus I've started started to learn about millis(). Hopefully it will be a short learning curve, but I doubt it with me. Thanks for the links.

@david_2018 That sounds interesting. I'm still new to coding so I might not be able to pull it off but I'll look into it.

@hzrnbgy Thank you.

8

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