Nokia 5110 LCD number display problem

Question

I have a problem regarding a Nokia 5110 LCD display. I am currently building a soldering station based on a PID controller. The original code was using a 7 segment display and I adapted the code to the Nokia display.

The problem is that when I rotate the potentiometer, the "read temp" and "set temp" is showing the exactly the same number, and after I finish rotating the potentiometer, the values return to their normal number.

How can I solve this problem ?

This is my code: https://pastebin.com/inPtkniX

This is the original project: https://www.allaboutcircuits.com/projects/do-it-yourself-soldering-station-with-an-atmega8/

//Soldering station Software using PID
//Thank you Alex from https://geektimes.ru/ for help with led array function
//AllAboutCircuits.com
//epilepsynerd.wordpress.com

#include <PID_v1.h>
#include <PCD8544.h>

PCD8544 lcd;
unsigned long updaterate = 500; //Change how fast the display updates. No lower than 500
unsigned long lastupdate;
int temperature = 0;
//Define Variables we'll be connecting to
double Setpoint, Input, Output;
//Define the aggressive and conservative Tuning Parameters
double aggKp = 4, aggKi = 0.2, aggKd = 1;
double consKp = 1, consKi = 0.05, consKd = 0.25;
//Specify the links and initial tuning parameters
PID myPID(&Input, &Output, &Setpoint, consKp, consKi, consKd, DIRECT);

void setup() {
  lcd.begin(84, 48);
  //We do not want to drive the soldering iron at 100% because it may burn, so we set it to about 85% (220/255)
  myPID.SetOutputLimits(0, 220);
  myPID.SetMode(AUTOMATIC);
  lastupdate = millis();
  Setpoint = 0;
}

void loop() {
  lcd.clear();
  //Read temperature
  Input = analogRead(0);
  //Transform the 10bit reading into degrees celsius
  Input = map(Input, 0, 450, 25, 350);
  //Display temperature
  if (millis() - lastupdate > updaterate) {
    lastupdate = millis();
    temperature = Input;
  }
  //Read setpoint and transform it into degrees celsius(minimum 150, maximum 350)
  double newSetpoint = analogRead(1);
  newSetpoint = map(newSetpoint, 0, 1023, 150, 350);
  //Display setpoint
  if (abs(newSetpoint - Setpoint) > 3) {
    Setpoint = newSetpoint;
    //temperature = newSetpoint;
    lastupdate = millis();
  }
  double gap = abs(Setpoint - Input); //distance away from setpoint
  if (gap < 10) {
  //we're close to setpoint, use conservative tuning parameters
    myPID.SetTunings(consKp, consKi, consKd);
  } else {
    //we're far from setpoint, use aggressive tuning parameters
    myPID.SetTunings(aggKp, aggKi, aggKd);
  }
  myPID.Compute();
  //Drive the output
  analogWrite(11, Output);
  //Display the temperature
  show(temperature, newSetpoint);
}

void show(int value, int newspnt) {
  lcd.setCursor(0, 0);
  lcd.print("READ TEMP");
  lcd.setCursor(0, 1);
  lcd.print(value);
  lcd.setCursor(0, 2);
  lcd.print("SET TEMP");
  lcd.setCursor(0, 3);
  lcd.print(newspnt);
  delay(200);
}

Answer 1

Look at line 55, where you are doing this

temperature = newSetpoint;

There is no reason to give temperature the same value as the set point. It does not make sense. And the temperature variable is the same, that you are using to display.

So, while you are changing the setpoint, the temperatur variable gets overwritten with the setpoint. When you are not changing it anymore, the measured temperature is still in this variable, when you are displaying it.

Just remove the mentioned line.