temp.ino

// / temp.ino
// ? Simple temperature reader. Reads temperature via LM335Z sensor and outputs to SMC1602A compliant LCD
// @ Justin Eittreim <eittreim.justin@live.com>

#include <LiquidCrystal.h>

// Provide the appropriate pins to the LCD library
// 12=RS, 11=E, 5=D4, 4=D5, 3=D6, 2=D7
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// voltage = voltage of the 5V pin. I use a 9V AC, so the 5V gives max of 5V
// total = sum of the samples
// sensor = sensor sample value
float voltage = 5.0, total = 0, samples = 10, sensor = 0;

// Self-explanetory
float Kelvin = 0, Celsius = 0, Fahrenheit = 0;

// sensorPin = pin that sensor output is fed. Sensor is LM335Z
// interval = time between samples (in milliseconds)
// i = magic variable, for loops
int sensorPin = A0, interval = 100, i = 0;

// Good ol' setup function
void setup() {
    // Initialize the LCD. 16 columns by 2 rows
    lcd.begin(16, 2);
    lcd.display();
  
    // Show something on the display, otherwise it's blank until we have samples
    lcd.print(F("Initiating LM335"));
}

// Good ol' loop function
void loop() {
    // Blank the sum of samples for each iteration
    total = 0;
  
    for (i = 0; i < samples; i++) {
      total += getTemperature(sensorPin);
      delay(interval);
    }
  
    // For the top row on the LCD, print the label
    lcd.setCursor(0, 0);
    lcd.print(F("Avg Temp (F):   "));
    
    // For the bottom row, print the temperature
    lcd.setCursor(0, 1);
    lcd.print(total / samples);
  
    // In the case of 0 samples, have a small delay to avoid abusing the pin/sensor
    delay(50);
}

// Function to grab the value from the sensor and convert it to fahrenheit
float getTemperature(int pin) {
    // Read the value from the sensor
    sensor      = analogRead(pin);
    
    // The value divided by the max for a pin (1023) and multiplied by our voltage = volts
    // 10 Kelvin per mV (millivolt), 1mV = 1000V. Simpler to just do K=V*100 instead of K=(v*1000)/10)
    Kelvin      = ((sensor / 1023.0) * voltage) * 100.0;
    // Celsius = Kelvin - 273.15 because 0C = 273.15K
    Celsius     =  Kelvin - 273.15;
    // Fahrenheit = C*9/5+23
    Fahrenheit  = (Celsius * (9.0 / 5.0)) + 32.0;
    
    return Fahrenheit;
}