Temperature sensor bugs

Question

My project is based on a moving fan using DHT11 sensors. I have used 2 void loops and the IDE is showing an error

"exit status 1 redefinition of 'void loop()'"

One doubt: Can we use 2 void loops in the code? Please see and identify the errors.

2nd doubt: dht DHT; shows error

"exit status 1 'dht' does not name a type" for my version of Arduino 1.8.1

#include <DHT.h>
#include <DHT_U.h>
#include <Adafruit_Sensor.h>
 // Including library for dht
#include<LiquidCrystal.h>
LiquidCrystal lcd(2, 3, 4, 5, 6, 7);
#define dht_dpin 12
dht DHT;
#define pwm 9
void setup() {
 // put your setup code here, to run once:
}
void loop() {
 // put your main code here, to run repeatedly:
 // put your setup code here, to run once:
 lcd.begin(16, 2);
 lcd.clear();
 lcd.print(" Fan Speed");
 lcd.setCursor(0,1);
 lcd.print(" Controlling");
 delay(2000);
 analogWrite(pwm, 255);
 lcd.clear();
 lcd.print("Circuit Digest ");
 delay(2000);
}
void loop() {
 DHT.read11(dht_dpin);
 int temp=DHT.temperature;
 lcd.setCursor(0,0);
 lcd.print("Temperature:");
 lcd.print(temp); // Printing temperature on LCD
 lcd.print("oC");
 lcd.setCursor(0,1);
 if(temp <26 ) {
 analogWrite(9,0);
 lcd.print("Fan OFF");
 delay(100);
 } else if(temp==26) {
 analogWrite(pwm, 51);
 lcd.print("Fan Speed: 20%");
 delay(100);
 } else if(temp==27) {
 analogWrite(pwm, 102);
 lcd.print("Fan Speed: 40%");
 delay(100);
 } else if(temp==28) {
 analogWrite(pwm, 153);
 lcd.print("Fan Speed: 60%");
 delay(100);
 } else if(temp==29) {
 analogWrite(pwm, 204);
 lcd.print("Fan Speed: 80%");
 delay(100);
 } else if(temp>29) {
 analogWrite(pwm, 255);
 lcd.print("Fan Speed: 100%");
 delay(100);
 }
 delay(3000);
}
}

• Jot: There can be only one loop() function, and you have two.
• SHILADITYA DEY: Two void loops are not allowed, why do you need one??
• Reshu Singh: After I remove the 2nd loop,then also there is an error.
• SHILADITYA DEY: send me the code after removing the loop, and also be specific about what you are trying to do.
• Edgar Bonet: "dht DHT;": You mean DHT dht;. The syntax is type_name variable_name; and the type name is DHT (upper case).

Answer 1

Here, below is updated version of your code.

Before running this code, you have to download DHT library. Just click on Click Here and you find good explanation & library of DHT11 Sensor. Becuase this library I usually preferred for my code. So, please download it and then run my code.

Click Here

And two void() loop never used. Put your all logic in one void() loop.

Note: This is not tested code. So if you face any problem then update me.

#include <dht.h> // DHT library
#include<LiquidCrystal.h> // LCD library
LiquidCrystal lcd(2, 3, 4, 5, 6, 7);
dht DHT;
#define DHT11_PIN 12
#define pwm 9
float temp;
void setup()
{
 Serial.begin(9600);
 pinMode(pwm, OUTPUT); //Pin as OUTPUT
}
void loop()
{
 int chk = DHT.read11(DHT11_PIN);
 temp = DHT.temperature;
 Serial.print("Temperature = ");
 Serial.print("\t");
 Serial.print(temp);
 delay(1000);
 lcd.begin(16, 2);
 lcd.clear();
 lcd.setCursor(0, 0);
 lcd.print("Fan Speed");
 lcd.setCursor(0, 1);
 lcd.print("Controlling");
 delay(2000);
 lcd.clear();
 lcd.setCursor(0, 0);
 lcd.print("Circuit Digest");
 delay(2000);
 lcd.clear();
 lcd.setCursor(0, 0);
 lcd.print("Temperature:");
 lcd.setCursor(10, 0);
 lcd.print(temp);
 lcd.setCursor(0, 1);
 if(temp < 26 )
 { 
 analogWrite(pwm, 0);
 lcd.print("Fan OFF");
 delay(100);
 }
 else if(temp == 26)
 {
 analogWrite(pwm, 51);
 lcd.print("Fan Speed: 20%");
 delay(100);
 }
 else if(temp == 27)
 {
 analogWrite(pwm, 102);
 lcd.print("Fan Speed: 40%");
 delay(100);
 }
 else if(temp == 28)
 {
 analogWrite(pwm, 153);
 lcd.print("Fan Speed: 60%");
 delay(100);
 }
 else if(temp == 29)
 {
 analogWrite(pwm, 204);
 lcd.print("Fan Speed: 80%");
 delay(100);
 }
 else if(temp > 29)
 {
 analogWrite(pwm, 255);
 lcd.print("Fan Speed: 100%");
 delay(100);
 } 
}