Using an Arduino Nano + I2C LCD + DS18B20 temperature display example part 2:

Here is the temp converted from Celsius to Fahrenheit...

iPhone photo - I2C LCD showing the DS18B20 in F

The initial example was in Celsius but that makes life confusing when you live in an area where everything is measured in Fahrenheit. I wanted to see how complex the conversion between C & F was so I tweaked my code from the last example.

//Initial I2C LCD example from:
// http://arduino-info.wikispaces.com/LCD-Blue-I2C

// Initial DS18B20 example from:
// http://bildr.org/2011/07/ds18b20-arduino/

// Read the DS18B20 and then write to an I2C LCD and serial monitor
// http://www.hoaglun.com/blog/2013/1/31/ds18b20-in-fahrenheit

//The formula to convert Celsius to Fahrenheit
//Ftemp = (CTemp * 9.0)/ 5.0 + 32.0;


#include <Wire.h> 
#include <OneWire.h> 
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,16,2);  // set the LCD address to 0x27 for a 16 chars and 2 line display


int DS18S20_Pin = 2; //DS18S20 Signal pin on digital 2

//Temperature chip i/o
OneWire ds(DS18S20_Pin);  // on digital pin 2

void setup(void) {
  Serial.begin(9600);
  lcd.init();                      // initialize the lcd 
 
  // Print a message to the LCD.
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("Nano+I2C+DS18B20");
//  lcd.setCursor(0, 1); 
//  lcd.print("Second Line");



}

void loop(void) {
  float tempC = getTemp();
  float tempF = (tempC * 9.0)/ 5.0 + 32.0;
  Serial.println(tempF);
  lcd.setCursor(0, 1); 
  lcd.print(tempF);
   delay(100); //just here to slow down the output so it is easier to read
  
}


float getTemp(){
  //returns the temperature from one DS18S20 in DEG Celsius

  byte data[12];
  byte addr[8];

  if ( !ds.search(addr)) {
      //no more sensors on chain, reset search
      ds.reset_search();
      return -1000;
  }

  if ( OneWire::crc8( addr, 7) != addr[7]) {
      Serial.println("CRC is not valid!");
      return -1000;
  }

  if ( addr[0] != 0x10 && addr[0] != 0x28) {
      Serial.print("Device is not recognized");
      return -1000;
  }

  ds.reset();
  ds.select(addr);
  ds.write(0x44,1); // start conversion, with parasite power on at the end

  byte present = ds.reset();
  ds.select(addr);    
  ds.write(0xBE); // Read Scratchpad

  
  for (int i = 0; i < 9; i++) { // we need 9 bytes
    data[i] = ds.read();
  }
  
  ds.reset_search();
  
  byte MSB = data[1];
  byte LSB = data[0];

  float tempRead = ((MSB << 8) | LSB); //using two's compliment
  float TemperatureSum = tempRead / 16;
  
  return TemperatureSum;
  
}

To find the formula and implement it took about 10 minutes. It would probably be shorter if I actually worked with this platform often enough to retain the structure in my brain. :-)

73 de NG0R