Problem with if condition

Question

So my project is including detecting the temperature in the room by using dth11 sensor. my idea is to add 3 LED lights were each light represent the temperature if its cold or hot or perfect.

the wiring and coding is done and it's working .However, i'm having a problem were the perfect temperature is always on no matter if the temperature is hot or cold. example: if the temperature is cold the cold LED will blink and the perfect temperature LED will be on.

#include <Adafruit_Sensor.h>
#include <DHT.h>
#define DHTPIN A0
#define DHTTYPE DHT11
#define LED_TOO_COLD 6
#define LED_PERFECT 8
#define LED_TOO_HOT 7
DHT dht(DHTPIN, DHTTYPE);
void setup() {
  Serial.begin(9600);
  Serial.println("DHT11 test!");

  dht.begin();
}

void loop() {

  pinMode (6 , OUTPUT);
  pinMode (7 , OUTPUT);
  pinMode (8 , OUTPUT);
  delay(2000);

  float h = dht.readHumidity();
  float t = dht.readTemperature();
  float f = dht.readTemperature(true);


  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  Serial.print("Humidity: ");
  Serial.print(h);
  Serial.print(" %\t");
  Serial.print("Temperature: ");
  Serial.print(t);
  Serial.println(" *C ");
  if (t < 22) {
    Serial.println("Too cold!");
    digitalWrite(6, HIGH);
    digitalWrite(7, LOW);
    digitalWrite(8, LOW);
    delay (2000);
  }
   if (t >26) {
    Serial.println("Too hot!");
    digitalWrite(7, HIGH);
    digitalWrite(6, LOW);
    digitalWrite(8, LOW);
    delay (2000);


  } else {
    Serial.println("Perfect temperature!");
    digitalWrite(8, HIGH);
    digitalWrite(6, LOW);
    digitalWrite(7, LOW);
    delay (2000);
  }

}

JVic · Accepted Answer · 2020-03-22 01:22:52Z

firstly, move your pinMode() settings to setup section.

in your code, when the temperature is 21 active pin will be 6 and 8. you should rewrite your code in next ways:

1:

if (t < 22) {
  ... its cold temp ...
} else if (t > 26) {
  ... its hot temp ...
} else {
  ... it's nor temp ...
}

2:

if (t < 22) {
   ... its cold temp ...
}
if (t > 26) {
   ... it's hot temp ...
} 
if (t >= 22 && t <= 26) {
   ... it's nor temp ...
}

and my small advice for u, rewrite in this way, it is more readable

digitalWrite(6, HIGH);
digitalWrite(7, LOW);
digitalWrite(8, LOW);

digitalWrite(6, LOW);
digitalWrite(7, HIGH);
digitalWrite(8, LOW);

digitalWrite(6, LOW);
digitalWrite(7, LOW);
digitalWrite(8, HIGH);

visually changing ENUMS (like LOW or HIGH) more noticeable than changing numbers (6/7/8)

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