Need help in coding an if else statment

nuggexts · April 27, 2024, 4:55am

Hello. For my project, I would like to make a heat pad that turns on automatically by sensing a presence, and when it reaches a specific temperature, the heat pad will turn off. For this project, I'm using an Arduino Uno, a DHT 11 for the temperature sensor, an i2c display (so it can display the temperature), a relay, and an HC-SR04 ultrasonic sensor (for automation purposes).

The condition wherein it will turn off after reaching a specific temperature works fine, but the ultrasonic sensor part doesn't work and I'm kind of stuck.

The step-by-step of what my project should be like:

The ultrasonic sensor will sense a presence, and it will turn the whole system on
The DHT11 will sense if the temperature is below or above 40 degrees Celsius. If it's below, the heat pad will turn on, else, it will turn off.
When the presence is gone, the whole system will also turn off.

Here's the schematic diagram:

Here's the coding:

#include <Wire.h>
#include <DHT.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,  16, 2);

#define DHTPIN 7
#define DHTTYPE DHT11

int relay1 = 3;
int relay2 = 4;
int temp = 7;
int dist = 9;

const int trigPin = 8;
const int echoPin = 9;

DHT dht(DHTPIN, DHTTYPE);

float duration, distance;

void setup() {

pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);

  Serial.begin(9600);

pinMode(relay1, OUTPUT);
pinMode(relay2, OUTPUT);


dht.begin();

lcd.init();
lcd.clear();
lcd.backlight();

}

void loop() {

  one();
  two();
  three();

  delay(2000);
  }
  void one() {
    if (dist > 50.0) {
      digitalWrite(relay1, HIGH);
    }
    else {
      digitalWrite(relay1, LOW);
    }
  }
  void two() {
    float dhtHumidity = dht.readHumidity();
    float dhtTemperature = dht.readTemperature();

    delay(1000);

  lcd.setCursor(0,0);

  lcd.print("Temp: ");
  lcd.print(dhtTemperature);
  lcd.print(" C");

  lcd.setCursor(0,1);
  lcd.print("Humid: ");
  lcd.print(dhtHumidity);
  lcd.print(" H");
  }

  void three() {
    temp = dht.readTemperature();
      if (temp < 40) {
      digitalWrite(relay1, LOW);
      }
      else {
      digitalWrite(relay1, HIGH);
      }
     }

  void four() {
    digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = (duration*.0343)/2;
  delay(100);
  }

Any replies will be highly appreciated!

Note: I'm a high school STEM student who doesn't have any background in coding. I'm just doing this for a capstone project

AresXT · April 27, 2024, 5:05am

your never called the function four() it reads the value of ultrasonic sensors

cattledog · April 27, 2024, 5:05am

In your code you never call function four( ) which has the distance measurement.

nuggexts · April 27, 2024, 6:11am

Update:

The ultrasonic-relay connection now works. However, the temperature condition doesn't work. Even if the heat pad exceeds 40 degrees Celsius, it's still on.

To be clear, its goal is to turn off when it exceeds 40 degrees Celsius and turn on when it's below 40 degrees Celcius. It must turn off even with presence from the ultrasonic sensor

Here's the code:

#include <Wire.h>
#include <DHT.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,  16, 2);

#define DHTPIN 7
#define DHTTYPE DHT11

const int trigPin = 8;
const int echoPin = 9;

int relay2 = 4;
int temp = 7;

DHT dht(DHTPIN, DHTTYPE);

float duration, distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(relay2, OUTPUT);

  Serial.begin(9600);
  
  dht.begin();

  lcd.init();
  lcd.clear();
  lcd.backlight();
}

void loop() {

  one();
  two();
  three();
  four();
}
  void one() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = (duration*.0343)/2;
  Serial.print("Distance: ");
  Serial.println(distance);
  delay(100);
  }

  void two() {
   if (distance > 50.0) {
      digitalWrite(relay2, HIGH);
    }
    else {
      digitalWrite(relay2, LOW);
    }
  }

  void three() {
    float dhtHumidity = dht.readHumidity();
    float dhtTemperature = dht.readTemperature();

    delay(1000);

   lcd.setCursor(0,0);

   lcd.print("Temp: ");
    lcd.print(dhtTemperature);
    lcd.print(" C");

    lcd.setCursor(0,1);
    lcd.print("Humid: ");
    lcd.print(dhtHumidity);
   lcd.print(" H");
  }

  void four() {
    temp = dht.readTemperature();
      if (temp < 40) {
      digitalWrite(relay2, LOW);
      }
      }

DaveEvans · April 27, 2024, 6:15am

Well, now "four" doesn't have the "turn off if too hot" part:

void four() {
    temp = dht.readTemperature();
      if (temp < 40) {
      digitalWrite(relay2, LOW);
      }
      }

Also, to help properly format your code and make it more readable for you and others, do this before posting:

And, I suspect that this is not going to do what you want:

  void two() {
   if (distance > 50.0) {
      digitalWrite(relay2, HIGH);
    }
    else {
      digitalWrite(relay2, LOW);
    }
  }

two() and four() may be fighting each other if the distance is <= 50
.
.
.
PS: interesting choice of projects considering that...

...capstone project is a multifaceted academic experience typically required for students during the final year of an academic program. It is a comprehensive and interdisciplinary project that often requires students to apply the knowledge and skills acquired throughout their academic careers....

nuggexts · April 27, 2024, 6:25am

That makes sense. How can I stop the contradiction between two() and four() when the distance is less than or equal to 50? I can't seem to think of a solution for it.

Also, my capstone project was assigned to me by the teacher so I don't have a choice but to do it even if it's challenging for me.

build_1971 · April 27, 2024, 6:40am

Call two() from four() only if temperature is below 40 degC.
And consider to give your functions a sensible name....

nuggexts · April 27, 2024, 6:44am

How would I do calling two() from four()? I'm sorry I don't know Arduino language. To be clear, what I should do is make an if/else statement for two() and four()?

I also gave my functions from what I think is a sensible name:
void one() = void ultrasonic()
void two() = void ultrarelay()
void three () = void tempreading()
void four() = tempcondition()

build_1971 · April 27, 2024, 7:04am

You really should do a course on C++ basics.
Look here (or somewhere else):

In four:

void four() {
    if (t<40) {
         do_whatever_needs_done;
         two();  //call function two()
     }
     else {
         blablabla;
     }
}

And remove two() from loop()

nuggexts · April 27, 2024, 7:16am

thanks!!

nuggexts · April 27, 2024, 11:45am

Update with this one, the condition still only follows the ultrasonic sensor command. I tried to undo the names of the functions since it made it more confusing to me.

#include <Wire.h>
#include <DHT.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);

#define DHTPIN 7
#define DHTTYPE DHT11

const int trigPin = 8;
const int echoPin = 9;

int relay2 = 4;
int temp = 7;

DHT dht(DHTPIN, DHTTYPE);

float duration, distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(relay2, OUTPUT);

  Serial.begin(9600);

  dht.begin();

  lcd.init();
  lcd.clear();
  lcd.backlight();
}

void loop() {

  one();
  three();
  four();
}
void one() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = (duration * .0343) / 2;
  Serial.print("Distance: ");
  Serial.println(distance);
  delay(100);
}

void three() {
  float dhtHumidity = dht.readHumidity();
  float dhtTemperature = dht.readTemperature();

  delay(1000);

  lcd.setCursor(0, 0);

  lcd.print("Temp: ");
  lcd.print(dhtTemperature);
  lcd.print(" C");

  lcd.setCursor(0, 1);
  lcd.print("Humid: ");
  lcd.print(dhtHumidity);
  lcd.print(" H");
}

void four() {
  temp = dht.readTemperature();
  if (temp > 40) {
    digitalWrite(relay2, HIGH);
  }
  one();
  {
    if (distance > 50.0) {
      digitalWrite(relay2, HIGH);
    } else {
      digitalWrite(relay2, LOW);
    }
  }
}

The good thing is that the heat pad doesn't turn on when the distance is < 50, but the bad thing is that it only turns off when the distance is < 50 despite the temperature exceeding 40 degree Celcius

build_1971 · April 27, 2024, 12:06pm

This should probably be inside the if block.
Move it inside the curly braces...
{}

And you really need to learn the basics...

nuggexts · April 27, 2024, 2:15pm

It's been 2 hours of trying to find the right code. Putting the one() inside the if block turned the relay on even when the distance is < 50. In one code that I have tried like this one:

void four() {
  temp = dht.readTemperature();
  //If distance is less than 50, ON
  if (distance > 50.0) {
    digitalWrite(relay2, HIGH);
//if relay is ON
    if (relay2 == HIGH) {
//if relay is ON and temp is < 40, OFF
      if (temp < 40) {
        digitalWrite(relay2, LOW);
      }
    }
//if distance is < 50, OFF
  } else {
    digitalWrite(relay2, LOW);
  }
}

The same thing happens, the ultrasonic sensor condition is the only one working.
I kind of understand the principle of an if-else statement, I just can't find what part I'm still doing wrong.

build_1971 · April 27, 2024, 2:22pm

if (relay2 == HIGH) {

relay2 holds the pin number, not the state of the relay...

Also, if you set the relay high, it is of no use to test if it is still high the very next line...

nuggexts · April 27, 2024, 2:32pm

My head hurts already lol. I tried to make a "much simpler" code. This doesn't work but this is how I would like it to work:

void four() {
  temp = dht.readTemperature();
  if ((distance < 50) && (temp < 40)) {
    digitalWrite(relay2, LOW);
  }
  if ((distance < 50) && (temp > 40)) {
    digitalWrite(relay2, LOW);
  }
  if ((distance > 50) && (temp < 40)) {
    digitalWrite(relay2, LOW);
  }
  if ((distance) < 50 && (temp > 40)) {
    digitalWrite(relay2, HIGH);
  }
}

With this code, it stays on no matter what

ruilviana · April 27, 2024, 2:33pm

nuggexts:

void four() {
  temp = dht.readTemperature();
  //If distance is less than 50, ON
  if (distance > 50.0) {
    digitalWrite(relay2, HIGH);
//if relay is ON
    if (relay2 == HIGH) {
//if relay is ON and temp is < 40, OFF
      if (temp < 40) {
        digitalWrite(relay2, LOW);
      }
    }
//if distance is < 50, OFF
  } else {
    digitalWrite(relay2, LOW);
  }
}

Simplify:

Try this code:

#include <Wire.h>
#include <DHT.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
#define DHTPIN 7
#define DHTTYPE DHT11
#define trigPin  8
#define echoPin  9
#define relay2  4
DHT dht(DHTPIN, DHTTYPE);
int temp = 7;
float duration, distance;
//--------------------------------------------------------------------
void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(relay2, OUTPUT);
  Serial.begin(9600);
  dht.begin();
  lcd.init();
  lcd.clear();
  lcd.backlight();
}
//--------------------------------------------------------------------
void loop() {
  one();
  three();
  four();
}
//--------------------------------------------------------------------
void one() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = (duration * .0343) / 2;
  Serial.print("Distance: ");
  Serial.println(distance);
  delay(100);
}
//--------------------------------------------------------------------
void three() {
  float dhtHumidity = dht.readHumidity();
  float dhtTemperature = dht.readTemperature();
  //delay(1000);
  lcd.setCursor(0, 0);
  lcd.print("Temp: ");
  lcd.print(dhtTemperature);
  lcd.print(" C");
  lcd.setCursor(0, 1);
  lcd.print("Humid: ");
  lcd.print(dhtHumidity);
  lcd.print(" H");
}
//--------------------------------------------------------------------
void four() {
  temp = dht.readTemperature();
  if (distance < 50.0 and temp < 40) {            
    digitalWrite(relay2, HIGH);
  }
  if (distance >= 50.0 or temp >= 40) {           
    digitalWrite(relay2, LOW);
  }
}

camsysca · April 27, 2024, 2:35pm

You still want it on, with nothing present? I guess I misunderstood you.

nuggexts · April 27, 2024, 2:43pm

I want it off when nothing is present

cattledog · April 27, 2024, 2:50pm

Then why do you turn it on when the distance is >50?

nuggexts · April 27, 2024, 2:53pm

OMG! This one worked! I just swapped where the HIGH and LOW conditions were. Thank you for all of those who replied to me, I appreciate you guys so much.

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Need help in coding an if else statment

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