problem with display

Using Arduino Programming Questions
1

hello,
i'm using a code to calculate alcohol concentration using mq-3 sensor. i hav a probleme in the lcd to display the result. The result must be : x.xxxx ppm but i receive the results in the wrong place and i can read it.
here the code :

#include "arduino.h"
#include <LiquidCrystal.h>
#include <sstream>
#include <string>
#include <iostream>

using namespace std;

float concentration(float x) {
  const float A[] = { 
    2.71494E+02, -3.10999E+02, 6.85051E+02, -3.47587E+02, 7.47499E+01            }; 
  float result;
  float B[4];
  B[0] = x*x;
  B[1] = B[0]*x;
  B[2] = B[1]*x;
  B[3] = B[2]*x;

  result = A[0]*x+A[1]*B[0]+A[2]*B[1]+A[3]*B[2]+A[4]*B[3];
  return result;
}

char messages[5][16] = {
  "Heating sensor", "64 seconds", "Autozero", "Ready!", "ppm"};

int L;
float x;
float x0[5];
float x_initial;

LiquidCrystal lcd(12, 11,5, 4, 3, 2); // Wiring microcontroller - LCD:

const int pushbutton = 8; // Pushbutton (normally open). Stops initial heating time when it is pressed. .
const int analogPin = A0; // Reads sensor voltage as a float int the interval (0-1) corresponding to (0 - 3.3V).

void text_screen( char messages[],  int colum, int row) {
  lcd.setCursor( colum, row);
  lcd.print(messages);
}



void setup() {

  lcd.clear(); 
  text_screen(messages[0], 0, 0);
  text_screen(messages[1], 0, 1);
  delay(2000);

  for (int j = 0; j<4; j++)
  {
    lcd.clear();  // Heating sensor 4x16 = 64 seconds
    text_screen(messages[0], 0, 0);


    for (int i = 0; i<16; i++){  
      if (pushbutton == 1){   // Pressing pushbutton stops initial heating and enters in measuring mode.
        break;
      }

      lcd.setCursor(i, 1);
      lcd.write(62);
      delay(1000);
    }
  }


  lcd.clear();
  text_screen(messages[2], 0, 0);
  delay(1000);


  float sensor_value_AnalogIn = 7; // Analog output to a multimeter or datalogger (1V = 1000 ppm).

  for (int i=0; i<5; i++)
  {
   x0[i]= analogRead(analogPin);
    delay(500);

  }
  x_initial = (x0[0]+x0[1]+x0[2]+x0[3]+x0[4])/5.0; // Autozero. Average of 5 initial measures.

  lcd.clear();
  text_screen(messages[3], 0, 0);
  delay(2000);

}

void loop()  {
  x = analogRead(analogPin);
  x = (x-x_initial)*3.3; // Calculate real voltage. 

  if(x<0)
    x = 0;

  x = concentration(x);
 
  delayMicroseconds(100);

  // Float to string conversion.
 char buffer[15];      // you need some space 

  dtostrf(x, 16, 5, buffer);

  lcd.clear();

  for (int i=0; i<strlen(buffer); i++)
  {
    lcd.setCursor(i,1);
    lcd.write(buffer[i]); 
  }
  text_screen(messages[4], 10, 0);
}

Thanks for help.

2

i receive the results in the wrong place

What wrong place? In what way is it wrong?

3

Yes - what do you expect, and what do you get? We can't see your screen from here (I know I have good eyesight, but it's not that good!)

Also:

  for (int i=0; i<strlen(buffer); i++)
  {
    lcd.setCursor(i,1);
    lcd.write(buffer[i]); 
  }

WTF?!

Simply:

lcd.setCursor(0, 1):
lcd.print(buffer);

Or, as you have already abstracted it:

text_screen(buffer, 0, 1);
4

thanks for reply,

The result is displayed on the top and right of the screen which is normally the location of the word "ppm", on the other hand, the results are displayed simultaneously on each other : like two superimposed map.

thank you.

5

char buffer[15]; // you need some space

dtostrf(x, 16, 5, buffer);

That's a recipe for disaster right there... Allocate 15 characters worth of space, then tell dtosrtrf() to use up to 16 of them...

6

ok.