Using IF statement with 2 LEDs

Projects Programming
1

I'm trying to have 1 of the LEDs light up when the condition is true, and turn off and light the other LED if it's false

#include <LiquidCrystal.h>
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
int Blue  = 8;
int Red = 9;
const int sensorPin = A0; 
int reading; 
float temperatureC; 
void setup()
{
lcd.begin(16, 2);
pinMode(Blue, OUTPUT);
digitalWrite(Blue, LOW);
pinMode(Red, OUTPUT);
digitalWrite(Red, LOW);


pinMode(sensorPin, INPUT); 
Serial.begin(9600);
} 
void loop()
{ reading = analogRead(sensorPin); 
temperatureC = (5.0 * reading* 100.0) / 1024; 
Serial.print(temperatureC); 
if (temperatureC >= 20){
digitalWrite(Red, HIGH);
digitalWrite(Blue, LOW);
}
else
{
  digitalWrite(Blue, HIGH);
  digitalWrite(Red, LOW);
}
lcd.setCursor(0, 0);
lcd.print("TEMP: ");
lcd.print(temperatureC);
lcd.print(" C");
delay(500); 
}

Both LEDs turn on when the temperature is less than 20, and both turn off when its more than 20.

2

Haveyoueverheartoflayout?Indentation?

pres ctrl+T and see how that looks :slight_smile:

Next, how did you connect those LEDs? I see nothing wrong (at least not with that) in the code.

After some rework:

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
const byte BlueLedPin = 8;
const byte RedLedPin = 9;
const byte SensorPin = A0;


void setup(){
  lcd.begin(16, 2);
  pinMode(BlueLedPin, OUTPUT);
  //digitalWrite(Blue, LOW); //the default
  pinMode(RedLedPin, OUTPUT);
  //digitalWrite(Red, LOW); //the default

  //pinMode(sensorPin, INPUT); //only applies to the digital mode
  Serial.begin(9600);
}
void loop(){
  unsigned int reading = analogRead(sensorPin);
  float temperatureC = (5.0 * reading * 100.0) / 1024;
  Serial.print(temperatureC);
  
  if (temperatureC >= 20) {
    digitalWrite(RedLedPin, HIGH);
    digitalWrite(BlueLedPin, LOW);
  }
  else{
    digitalWrite(BlueLedPin, HIGH);
    digitalWrite(RedLedPin, LOW);
  }
  
  lcd.setCursor(0, 0);
  lcd.print("TEMP: ");
  lcd.print(temperatureC);
  lcd.print(" C");
  delay(500);
}

Also note, a float does NOT simply mean a decimal point and is pretty hard for a Uno to do.

3

I connected longer part of the LED to a resistor, then the pin, and the shorter part to the ground. The rework still has the same problem. Thanks for helping out btw.

4

The rework had nothing to do with the problem :slight_smile:

But at all times, only one of the two leds is lit?