How to shorten this code (because my sensor reads slowly)?

Question

I'm making a fare meter for our school project. I have too much lcd.print code. This code is not finished yet. My only concern is how to minimize the usage of lcd.print. I think it's the one that makes my sensor reading slow.

I'm new at Arduino; sorry if I have too many mistakes. I appreciate any of your answers. Thank you!

#include <LiquidCrystal_I2C.h>
#include <Wire.h>
#include <virtuabotixRTC.h>
virtuabotixRTC myRTC(6, 7, 8);
float d[4] = {};
int x = 0;
int f = 0;
int dis = 0;
const uint8_t disBut = 13;
int input = A0;
int state = 0;
int disF = 0;
int buttonstate = 0;
LiquidCrystal_I2C lcd(0x27, 20, 4);
LiquidCrystal_I2C lcd1(0x26, 20, 4);
void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  lcd1.init();
  lcd1.backlight();
  pinMode(disBut, INPUT);
  pinMode(buttonstate, OUTPUT);
}
void loop() {

  myRTC.setDS1302Time(18, 10, 10, 7, 18, 9, 2020);
Serial.print("Current Date / Time: ");
  Serial.print(myRTC.dayofmonth);
  Serial.print("/");
  Serial.print(myRTC.month);
  Serial.print("/");
  Serial.print(myRTC.year);
  Serial.print("  ");
  Serial.print(myRTC.hours);
  Serial.print(":");
  Serial.print(myRTC.minutes);
  Serial.print(":");
  Serial.println(myRTC.seconds);
  delay(500);
d[0] = (x * 1.73);
  d[1] = (x * 1.73);
  d[2] = (x * 1.73);
  d[3] = (x * 1.73);
lcd.setCursor(8, 0);
  lcd.print(d[0]);
  lcd.setCursor(8, 1);
  lcd.print(d[1]);
  lcd.setCursor(8, 2);
  lcd.print(d[2]);
  lcd.setCursor(8, 3);
  lcd.print(d[3]);
lcd.setCursor(0, 0);
  lcd.print(F("P1"));
  lcd.setCursor(0, 1);
  lcd.print(F("P1"));
  lcd.setCursor(0, 2);
  lcd.print(F("P1"));
  lcd.setCursor(0, 3);
  lcd.print(F("P1"));
lcd.setCursor(6, 0);
  lcd.print(F("D="));
  lcd.setCursor(6, 1);
  lcd.print(F("D="));
  lcd.setCursor(6, 2);
  lcd.print(F("D="));
  lcd.setCursor(6, 3);
  lcd.print(F("D="));
lcd1.setCursor(0, 0);
  lcd1.print(F("W="));
  lcd1.setCursor(0, 1);
  lcd1.print(F("W="));
  lcd1.setCursor(0, 2);
  lcd1.print(F("W="));
  lcd1.setCursor(0, 3);
  lcd1.print(F("W="));
lcd1.setCursor(6, 0);
  lcd1.print(F("dscnt="));
  lcd1.setCursor(6, 1);
  lcd1.print(F("dscnt="));
  lcd1.setCursor(6, 2);
  lcd1.print(F("dscnt="));
  lcd1.setCursor(6, 3);
  lcd1.print(F("dscnt="));
lcd1.setCursor(15, 0);
  lcd1.print(F("F="));
  lcd1.setCursor(15, 1);
  lcd1.print(F("F="));
  lcd1.setCursor(15, 2);
  lcd1.print(F("F="));
  lcd1.setCursor(15, 3);
  lcd1.print(F("F="));
int counter=digitalRead(A0);
  if (state == 0) {
    switch (counter) {
      case 1:
        state = 1;
        lcd.setCursor(11, 0);
        x = x + 1; lcd.print(x);
        break;
      case 0:
        state = 0;
        break;
    }
  }
if (counter == LOW)
    state = 0;
  if (state == 0) {
    switch (counter) {
      case 1:
        state = 1;
        x = x + 1;
        break;
      case 0:
        state = 0;
        break;
    }
  }
if (counter == LOW)
   state = 0;
}

Why do you think the sensor reading is slow? Do the measurement values update to slowly? How fast do you need it? Note that if the display updates too fast, you cannot read it. — PMF, Jan 23 '21 at 08:15
Only print to the display things that change. Put in the static text once and once only in setup, and only display the changing values when they actually change, rather than every single iteration of loop. — Majenko, Jan 23 '21 at 10:53

score 2 · Answer 1 · answered Jan 23 '21 at 11:47

Your slowness is because on every single iteration of loop() you are updating the entirety of the display. That's bad and wasteful.

You need to do two things:

Only display static information (the labels) once. Do that in setup().
Only display the variable data if it actually changes.

The first is simple: move any static text to setup(). That means things like lcd1.print(F("dscnt="));. It never changes, and the display doesn't "forget" it, so doesn't need constantly reminding.

The second is slightly harder. You need to keep two copies of the data. One that is the data at this moment, and one that is the data that is being displayed. Then you compare one with the other and for any items where they differ display them and update your saved copy.

So something like:

if (d[0] != d_saved[0]) {
    d_saved[0] = d[0];  
    lcd.setCursor(8, 0);
    lcd.print(d[0]);
}

You can of course make that easier to program with a loop:

for (uint8_t i = 0; i < 4; i++) {
    if (d[i] != d_saved[i]) {
        d_saved[i] = d[i];  
        lcd.setCursor(8, i);
        lcd.print(d[i]);
    }
}

Of course d_saved[4] needs creating in either the global scope or as a local static variable and initialising with some suitable "can never be" values (like -1 or something) so that the first time through it will always be different from the real values and display everything properly.

How to shorten this code (because my sensor reads slowly)?

1 Answers1