Why do I have to open Serial Monitor to display non nan values ?

Using Arduino Displays
#1

Why do I have to open Serial Monitor to display non nan values retrieved from DHT22, :confused:
what am I doing wrong in the code below ?

#include <DHT.h>
#include <Wire.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_GFX.h>
// OLED display TWI address
#define OLED_ADDR   0x3C
// reset pin not used on 4-pin OLED module
Adafruit_SSD1306 display(-1);  // -1 = no reset pin
// 128 x 64 pixel display
#if (SSD1306_LCDHEIGHT != 64)
#error("Height incorrect, please fix Adafruit_SSD1306.h!");
#endif
#define DHTPIN D3
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);
void setup() {

  delay(10);
  dht.begin();
  pinMode (DHTPIN, OUTPUT);
  /// initialize and clear display
  display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR);
  display.clearDisplay();
  //  display.drawRect(1, 1, display.width()-1, display.height()-1, WHITE);   // draws the outer rectangular boundary on the screen
  display.display();
  // display a pixel in each corner of the screen
  display.drawPixel(0, 0, WHITE);
  display.drawPixel(127, 0, WHITE);
  display.drawPixel(0, 63, WHITE);
  display.drawPixel(127, 63, WHITE);
  // display a line of text
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(20, 18);
  display.print("Welcome");
  display.setCursor(25, 40);
  display.print("San");
  
  // update display with all of the above graphics
  display.display();
}
void loop() {
  // put your main code here, to run repeatedly:
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 1);
  display.print("Showing Temperature");
  // display Temperature
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(1, 18);
  display.print("T : ");
  display.print(t);
  display.setTextSize(1);
  display.print((char)247);
  display.setTextSize(2);
  display.print("C");
  display.setCursor(1, 40);
  display.print("H : ");
  display.print(h);
  display.print(" %");
  // update display with all of the above graphics
  display.display();
}

After uploading code it does will display nan but when I open serial monitor it works fine displaying actual values from DHT22 :o

#2

it looks like the loop function is not getting executed at all, if I dont hit the serial monitor icon.

#3

Hi.

I have no idea what 'nan' is.
I do not see any serial communication in your sketch.
But opening the serial monitor, causes a reset.
Perhaps your screen needs some extra time to reset after power on.
So try to have a larger delay() in line 18, and if that doesn't help, put in some extra delays in other lines, just to test.

#4

Also posted at:

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#5

MAS3:
Hi.

I have no idea what 'nan' is.
I do not see any serial communication in your sketch.
But opening the serial monitor, causes a reset.
Perhaps your screen needs some extra time to reset after power on.
So try to have a larger delay() in line 18, and if that doesn't help, put in some extra delays in other lines, just to test.

thanks for reply, I tried your suggestion, but it didnt help. if i do not have serial monitor open loop function doesnt work. if I have serial monitor open the OLED updates, if i close serial monitor window the text on doest updates from the loop function.
why is loop function dependent on serial monitor window being open ?

#6

MAS3:
Hi.

I have no idea what ‘nan’ is.
I do not see any serial communication in your sketch.
But opening the serial monitor, causes a reset.
Perhaps your screen needs some extra time to reset after power on.
So try to have a larger delay() in line 18, and if that doesn’t help, put in some extra delays in other lines, just to test.

NAN is normally “No A Number” it is normally used to denote division by Zero.

It is difficult to provide any help to the other person since they did not indicate which Arduino board they are using.

I would suggest that they post the question on the adafruit forums. they may have some better insight into the workings or not workings of the adafruit devices.

#7

Are you using pin 0 or 1 by any chance ?

#8