Beginner Arduino loop function and variable - arduino

Question

This is the revised code, the initial value is reading ridiculously high without the conversion!! How do I get the conversion to apply to the initialTemp as well temperatureC?
The code you have helped with as far as I can tell is exactly what I was trying to achieve, but obviously.
Thanks again!!
int pin_tempRead = 0; // temperature sensor pin
int coolLED = 2; // cooling LED digital pin
int heatLED = 3; // heating LED digital pin
float initialTemp;
float cutOffTemp = 30; //cut off temperature = 30°C
void setup()
{
Serial.begin(9600); //Start the serial connection with the computer
pinMode(heatLED, OUTPUT); //initialise as OUTPUT
pinMode(coolLED, OUTPUT); //initialise as OUTPUT
initialTemp = analogRead(pin_tempRead); // read the initial temp
Serial.print("Initial temperature: "); Serial.print(initialTemp); Serial.println("C"); //prints out starting temperature
}
void loop() // run over and over again
{
//getting the voltage reading from the temperature sensor
float current_temp = analogRead(pin_tempRead);
// converting that reading to voltage
float voltage = current_temp * 5.0; voltage /= 1024.0;
float temperatureC = (voltage - 0.5) * 100 ; //converting from 10 mv per degree with 500 mV offset
//to degrees ((voltage - 500mV) times 100)
if(temperatureC > cutOffTemp) {
// temp too high -> turn on the cooling system
digitalWrite(heatLED, LOW);
digitalWrite(coolLED, HIGH);
}else if (temperatureC < initialTemp) {
// temp too low -> turn on the heating system
digitalWrite(heatLED, HIGH);
digitalWrite(coolLED, LOW);
}
Serial.print("Current pump temperature: ");
Serial.print(temperatureC); Serial.println("C");
delay(1000);
}

Answer 1

the loop() function executes over and over, so it's not a good place to store initial values.
What you need to do is define a global variable, initialize it inside the setup() function and then you can read it in the loop() function
Minimalist example:
int pin_tempRead = 0; // temperature sensor pin
float initial_temp; // define a global variable
void setup() {
initial_temp = analogRead(pin_tempRead); // read the initial temp
}
void loop() {
float current_temp = analogRead(pin_tempRead);
// get the temperature difference respect to the initial one
float difference = initial_temp - current_temp;
delay(1000);
}
PD: Also is a good practice to distinguish the variables defining a hardware connection (pins) from the software ones. I usually append pin_ to the variables that define connections. Otherwise is not clear if tempRead is the value of the temperature or the pin where the sensor is attached.
Also, for the turning on and off of the heater/cooling system: You are already in a loop (the loop() function is a loop) so you don't need a while loop.
And you have some problem with our logic.
As I understood, you want to heat until the higher threshold (cutOff) is reached, then cool down until the lower threshold is reached (initialTemperature).
This is called Hysteresis, but your logic was wrong, here's the corrected one:
Just do:
void loop() {
if(temperatureC > cutOffTemp) {
// temp too high -> turn on the cooling system
digitalWrite(heatLED, LOW);
digitalWrite(coolLED, HIGH);
}else if (temperatureC < initialTemp) {
// temp too low -> turn on the heating system
digitalWrite(heatLED, HIGH);
digitalWrite(coolLED, LOW);
}
Serial.print("Current pump temperature: ");
Serial.print(temperatureC); Serial.println("C");
delay(1000);
}
By the way, you are using the initialTemperature as the low threshold for turning on the heating.
Is that what you really want?
What if the initial temperature is higher that the cutOffTemp? You will have problems in that case since the lower threshold is higher than the higher threshold.