PD_Reflow_Hoteplate/firmware/reflow-v6/utils.ino

//Read Temp read the current temperature of the hotplate
/*
 * Read Current temperature from ADC
 * The ADC is reading from a voltage divider
 * 5V --- 1k Ohm --- (ADC) --- 100k NTC --- GND
 * 
 * ADC Reading / Temperature (degree C)
 * 250 / 25 
 * 225 / 100 
 * 155 / 160 (Preheat Temp)
 * 123 / 220 (Reflow Temp)
 * 100 / 240 (Hard cutoff Temp)
 * 
 * Each reading takes around 100ms
 */
int readTemp() {
  int numReadings = 10;  // Number of readings to average
  int totalSensorValue = 0;

  for (int i = 0; i < numReadings; ++i) {
    totalSensorValue += analogRead(TEMP_PIN);
    delay(10);  // Optional: add a small delay between readings if needed
  }

  // Calculate the average sensor value
  int averageSensorValue = totalSensorValue / numReadings;

  return averageSensorValue;
}

//enterStandbyMode move the hotplate state to standby and cutoff power to hotplate
void enterStandbyMode() {
  reflowing = false;
  USBSerial_println("Reflow Stopped");
  //Set target temperature to room temp and shut down heater
  targetTempADC = COOLDOWN_TEMP_ADC;
  targetPwrPWM = 0;

  //Set yellow LED to slow blinkRed
  digitalWrite(LED_REFLOW, LOW);
  digitalWrite(LED_PREHEAT, LOW);
  blinkYellow = true;
  blinkRed = false;
  fastblinkRed = false;

  //Set reflow stage to standby
  reflowStages = 0;
}

//Update heater power state base on temp reading
//The hotter the plate, the smaller the ADC reading
//Return true when the temperature is within target range
bool updateHeaterPowerState() {
  int currentADC = readTemp();
  if (currentADC <= CUTOFF_TEMP_ADC) {
    digitalWrite(HEATER_PIN, LOW);
    USBSerial_println("!!! OVERHEAT !!!");
    digitalWrite(LED_PREHEAT, HIGH);
    digitalWrite(LED_REFLOW, HIGH);
    return false;
  }
  if (currentADC > targetTempADC + offset) {
    //Temperature too low. Turn on the heater
    analogWrite(HEATER_PIN, targetPwrPWM);
    //USBSerial_print("+ ");
    //USBSerial_println(currentADC);
    return false;
  } else if (currentADC < targetTempADC - offset) {
    //Temperature too high. Turn off the heater
    analogWrite(HEATER_PIN, 0);
    //USBSerial_print("- ");
    //USBSerial_println(currentADC);
    return false;
  } else {
    //Within range. Keep the current state
    return true;
  }
}

//Update Key States handle touch button events listening and global state update
void updateKeyStates() {
  //Read the current buttons state
  updateButtonPressState();

  //Start button, require hold down for 3 seconds to start
  if (startPressed) {
    startCountdown--;
    if (startCountdown <= 0 && !reflowing) {
      if (stopPressed) {
        //Holding two buttons together. Enter desolder mode
        USBSerial_println("!!! Desolder Mode Started !!!");
        reflowing = true;
        startCountdown = 0;               //Prevent underflow counter
        playStartingLEDBlinks();          //Play fast blink start warning
        targetTempADC = REFLOW_TEMP_ADC;  //Set the target temp to reflow target temp
        targetPwrPWM = REFLOW_PWR_PWM;    //Set power rating to 100%
        reflowStages = 10;                //Set the reflow stage to desolder

        //Set red LED to blink fast
        blinkYellow = false;
        blinkRed = false;
        fastblinkRed = true;
      } else {
        //Holding start button only. Enter automatic reflow mode
        /* START REFLOW PROCESS - PREHEAT */
        USBSerial_println("!!! Reflow Started !!!");
        reflowing = true;
        startCountdown = 0;                 //Prevent it from going underflow
        playStartingLEDBlinks();            //Play fast blink start warning
        targetTempADC = PREHEAT_START_ADC;  //Set the target temp to preheat starting temp
        targetPwrPWM = PREHEAT_PWR_PWM;     //Set power rating to preheat
        reflowStages = 1;                   //Set the reflow stage to preheating

        //Set the blinking LED status to off
        blinkYellow = false;
        blinkRed = false;
        fastblinkRed = false;
        digitalWrite(LED_PREHEAT, HIGH);  //Light up the preheat LED
      }
      return;
    }
  } else {
    //Press released
    startCountdown = HOLDSTART_TIME;
  }

  //Stop button, stop immediately
  if (stopPressed) {
    enterStandbyMode();
  }
}