Quite down ATtiny84

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1

I am using an ATtiny84 to read a thermistor and print to a lcd. But, the temperature jumps around a lot. How can i get a more precise reading?

//THE THERMISTOR IS A 10K THERMISTOR
//                                          DIAGRAM
//  GROUND-----------10K RESISTOR-----------INPUT A0-----------10K THERMISTOR-----------5V

#include <LiquidCrystal.h>

LiquidCrystal lcd(0, 1, 2, 3, 4, 5);

int ValBL = 85;     //Value for BackLight Brightness
int BackLight = 6;  //BackLight PWM Output

int Thermostat = A7;
float ThermostatReading = 0;
float Res = 0;

float TempK = 0;    //Tempature in K
float TempC = 0;    //Tempature in C
float TempF = 0;    //Tempature in F
float L1 = 0;
float L2 = 0;
float L3 = 0;
float L4 = 0;
float L5 = 0;
float AvgK = 0;
int Avg = 1;        //Average the temp

void setup()
{
  pinMode(BackLight, OUTPUT);
  lcd.begin(16, 2);
  analogWrite(BackLight, ValBL);
}

void loop()
{
  Calibration();
  Resistance();
  Temperature();
  Average();
  Avg = Avg + 1;
  delay(200);
}

//Averages the tempatures
void Average()
{
  if (Avg == 1)
  {
    L1 = TempK;
  }
  if (Avg == 2)
  {
    L2 = TempK;
  }
  if (Avg == 3)
  {
    L3 = TempK;
  }
  if (Avg == 4)
  {
    L4 = TempK;
  }
  if (Avg == 5)
  {
    L5 = TempK;
    AvgK = (L1 + L2 + L3 + L4 + L5);
    AvgK = (AvgK / 5);
    TempConver();
    Avg = 1;
    PrintTemp();
  }
  if (Avg <= 0 || Avg >= 6)
  {
    Avg = 1;
  }
}

//Converts the reading to a resistance value
void Resistance()
{
  Res = analogRead(Thermostat);
  Res = 1023 / Res - 1;
  Res = 10000 / Res;
}

//Calculate Tempatuere
void Temperature()
{
  ThermostatReading = analogRead(Thermostat);
  TempK = log(10000.0 * (1024.0 / ThermostatReading - 1));
  TempK = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * TempK * TempK)) * TempK);
}

void TempConver()
{
  TempC = AvgK - 273.15;
  TempF = TempC * 1.8 + 32;
}

//Prints the Tempature and Resistance Output
void PrintTemp()
{
  lcd.clear();
  lcd.setCursor(2, 0);
  lcd.print(Res);
  lcd.print(" Ohm");
  lcd.setCursor(0, 1);
  lcd.print(TempC);
  lcd.print("C");
  lcd.setCursor(9, 1);
  lcd.print(TempF);
  lcd.print("F");
}

void Calibration()
{
  if (AvgK == 0)
  {
    lcd.clear();
    lcd.setCursor(2, 0);
    lcd.print("CALIBRATING");
    lcd.setCursor(2, 1);
    lcd.print("CALIBRATING");
  }
}
2

I guess that you are using the "clockwise pin mapping" compiler option for the ATTINY84 otherwise you have a conflict between digital pin 3 (used by the LCD) and analog pin 7 (used by the sensor).

To troubleshoot further, I'd suggest first of all writing the raw value of analogRead(Thermostat) to the display (maybe once per second) simply to see the state of the source data. If that is highly random, then no amount of smoothing will help. If it is, however, consistent, then you have to suspect your processing.

You could also look at a moving average type smoothing rather than a simple average over blocks of 5 results.