LCD not printing DHT info

Projects General Guidance
1

I don't know if it's the circuit or the code that's not correct. Trying to get Temp & Humidity to display on the I2C-LCD. My serial Monitor shows the DHT22 is sending good data. I previously had this working, however, I accidentally deleted the sketch. I tried to recreate the sketch. Can't find it on YouTube.
Is there supposed to be a "wire" library or something?
here is the coding:

#include <LiquidCrystal_I2C.h>

#include <DHT.h>
#include <DHT_U.h>

#define DHTPIN 2
#define DHTTYPE DHT22
DHT dht(DHTPIN,DHTTYPE);
LiquidCrystal_I2C lcd(0x27, 16, 2);
int br=9600;
int setUpDelay=3000;
int measDelay=5000;
float tempC;
float tempF;
float hum;
void setup() {
Serial.begin(br);
dht.begin();
delay(setUpDelay);
lcd.init();
lcd.backlight();
// put your setup code here, to run once:
}
void loop() {
tempC=dht.readTemperature(false);
tempF=dht.readTemperature(true);
hum=dht.readHumidity();

lcd.setCursor(0,0);
lcd.print("Temp: ");
lcd.print(tempF);
lcd.print("F ");
lcd.setCursor(0,1);
lcd.print("HUM: ");
lcd.print(hum);
lcd.print("%");

Serial.print("Temp: ");
Serial.print(tempC);
Serial.print(" Degrees C OR ");
Serial.print(tempF);
Serial.print(" Degrees F AND ");
Serial.print("Humidity is at: ");
Serial.print(hum);
Serial.println("%");
delay(measDelay);

}

This may help see wiring:
![20250427_213853|666x500](upload://cyR24VKXLtrcWhLj6chlDuoyS7u.jpeg)
2

Hello. Your text and image got stuck in the code block. Would you wrap the code the code block and remove the text and image?

3

It usually works better when we can see the picture:

20250427_213853
20250427_2138531920×1440 206 KB

But I'm afraid that's too out of focus to say anything other than "try adjusting the contrast".

4

Your code is OK,
See simulator:

5

mmm

I think there is a Wire.begin() missing in setup() to initialize the I2C bus.

@ruilviana
Is wire automatically initialized in WokWi?

6

IDK for sure but I would very certainly take any bet that it does not.

The code goes through a standard Arduino too chain, and is run on a nearly perfect emulation of the microprocessor.

Doing anything that woukd damage the fidelity and therefore the usefulness of it as a simulator would be contrary to the wokwi philosophy.

One thing it isn't too good (or fussy) about is electronics. So LEDs can be bright with just the internal weak pull-up and won't burn out if you don't use a series current-limiting resistor.

Some parts don't need explicit wiring of Vcc and GND.

And all the LEDs are unsatisfactory for comparison to what things will look like IRL.

a7

7

Even after adjusting contrast and brightness it is too unfocused to be of any help.

IMG_2367-resaved
IMG_2367-resaved1920×1440 417 KB

8

Inside LiquidCrystal_I2C.h at simulator there is a wire.h.

#ifndef LiquidCrystal_I2C_h
#define LiquidCrystal_I2C_h

#include <inttypes.h>
#include "Print.h" 
#include <Wire.h>


..........................
9

and does it call Wire.begin() ?

10

Your code works... so check your wiring... pin for pin... Verify every connection by removing all the wires and inserting the wires again. The length of the LCD wires might be too long for the I2C bus.

Add this line of code immediately after your last line of code. It will turn the built-in LED on the Uno ON then OFF on alternate reads of the DHT.

  digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));

Your code should look like this:

#include <LiquidCrystal_I2C.h>

#include <DHT.h>
#include <DHT_U.h>

#define DHTPIN 2
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);
LiquidCrystal_I2C lcd(0x27, 16, 2);
int br = 9600;
int setUpDelay = 3000;
int measDelay = 5000;
float tempC;
float tempF;
float hum;

void setup() {
  Serial.begin(br);
  dht.begin();
  delay(setUpDelay);
  lcd.init();
  lcd.backlight();
}

void loop() {
  tempC = dht.readTemperature(false);
  tempF = dht.readTemperature(true);
  hum = dht.readHumidity();

  lcd.setCursor(0, 0);
  lcd.print("Temp: ");
  lcd.print(tempF);
  lcd.print("F ");
  lcd.setCursor(0, 1);
  lcd.print("HUM: ");
  lcd.print(hum);
  lcd.print("%");

  Serial.print("Temp: ");
  Serial.print(tempC);
  Serial.print(" Degrees C OR ");
  Serial.print(tempF);
  Serial.print(" Degrees F AND ");
  Serial.print("Humidity is at: ");
  Serial.print(hum);
  Serial.println("%");
  delay(measDelay);

  digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN)); // <-- to blink built-in LED on Pin 13
}
11

Thank you for your help, time and suggestions. I'll tackle this again.

12

If you use the code in Post #10, be sure to watch the built-in LED for "blinking" when the DHT is read.

13

Now thats new to me. I'll be checking that out. Thanks!

14

Meanwhile I successfully ran the edited sketch below using a DHT11 (I have no DHT22). The other significant change was adding Wire.h

Let me know if you still need help with wiring.

#include <Wire.h> // my edit, seems necessary
#include <LiquidCrystal_I2C.h>
#include <DHT.h>
//#include <DHT_U.h>  // my edit, seems redundant

#define DHTPIN 2
//#define DHTTYPE DHT22
#define DHTTYPE DHT11  // my edit
DHT dht(DHTPIN, DHTTYPE);
LiquidCrystal_I2C lcd(0x27, 16, 2);
int br = 9600;
int setUpDelay = 3000;
int measDelay = 5000;
float tempC;
float tempF;
float hum;

void setup()
{
  pinMode(LED_BUILTIN, OUTPUT); // for the LED reassurance statement
   Serial.begin(br);
  delay(200); // my edit, to minimise spurious initial printing
  dht.begin();
  delay(setUpDelay);
  lcd.init();
  lcd.backlight();
}

void loop()
{
  tempC = dht.readTemperature(false);
  tempF = dht.readTemperature(true);
  hum = dht.readHumidity();

  lcd.setCursor(0, 0);
  lcd.print("Temp: ");
  lcd.print(tempF);
  lcd.print("F ");
  lcd.setCursor(0, 1);
  lcd.print("HUM: ");
  lcd.print(hum);
  lcd.print("%");

  Serial.print("Temp: ");
  Serial.print(tempC);
  Serial.print(" Degrees C OR ");
  Serial.print(tempF);
  Serial.print(" Degrees F AND ");
  Serial.print("Humidity is at: ");
  Serial.print(hum);
  Serial.println("%");
  delay(measDelay);

  digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN)); // <-- to blink built-in LED on Pin 13
}
15

Success! Everything works fine now. Oddly (to me) the only thing I changed was eliminating the breadboard power supply. Powered the rails with the Uno only.
that's it. and it started working. Thanks!

16

No common ground?

Anyway, happy ending :+1: Don't forget :white_check_mark: Solution the post that helped you the most.