Dallas Semiconductor (Maxim) produces a line of “One-Wire” devices, that allow multiple sensors to connect to a single data pin on a microcontroller. GND and +5vdc are also needed. I’ve put together a single sensor DS18B20 (soon to be expanded to multiple sensors) displaying the temperature on a LCD display. This example is digital, unlike the analog thermistor project from a few days ago. Enjoy, and please comment.

Find the address of your DS18B20

Become the Maker you were born to be. Try Arduino Academy for FREE!

// LCD Thermostat

#include <onewire.h>
#include <liquidcrystal.h>

// Connections:
// rs (LCD pin 4) to Arduino pin 12
// rw (LCD pin 5) to Arduino pin 11
// enable (LCD pin 6) to Arduino pin 10
// LCD pin 15 to Arduino pin 13
// LCD pins d4, d5, d6, d7 to Arduino pins 5, 4, 3, 2
LiquidCrystal lcd(12, 11, 10, 5, 4, 3, 2);
int backLight = 13; // pin 13 will control the backlight

OneWire ds(8); // ds18b20 pin #2 (middle pin) to Arduino pin 8
// ds18b20 pin #1 GND
// ds18b20 pin #3 +5vdc
// 5k ohm resistor between pins 2 & 3

byte i;
byte present = 0;
byte data[12];
byte addr[8];

int HighByte, LowByte, SignBit, Whole, Fract, TReading, Tc_100, FWhole;

void setup(void) {
pinMode(backLight, OUTPUT);
digitalWrite(backLight, HIGH); // turn backlight on. Replace ‘HIGH’ with ‘LOW’ to turn it off.
lcd.begin(2,16);              // rows, columns.  use 2,16 for a 2×16 LCD, etc.
lcd.clear();                  // start with a blank screen
lcd.setCursor(0,0);           // set cursor to column 0, row 0

if ( !ds.search(addr)) {
lcd.clear(); lcd.print(“No more addrs”);
delay(1000);
ds.reset_search();
return;
}

if ( OneWire::crc8( addr, 7) != addr[7]) {
lcd.clear(); lcd.print(“CRC not valid!”);
delay(1000);
return;
}
}

void getTemp() {
int foo, bar;

ds.reset();
ds.select(addr);
ds.write(0x44,1);

present = ds.reset();
ds.select(addr);
ds.write(0xBE);

for ( i = 0; i < 9; i++) {
data[i] = ds.read();
}

LowByte = data[0];
HighByte = data[1];
TReading = (HighByte << 8) + LowByte;
SignBit = TReading & 0x8000;  // test most sig bit

if (SignBit) {
TReading = -TReading;
}
Tc_100 = (6 * TReading) + TReading / 4;    // multiply by (100 * 0.0625) or 6.25
Whole = Tc_100 / 100;          // separate off the whole and fractional portions
Fract = Tc_100 % 100;
if (Fract > 49) {
if (SignBit) {
–Whole;
} else {
++Whole;
}
}

if (SignBit) {
bar = -1;
} else {
bar = 1;
}
foo = ((Whole * bar) * 18);      // celsius to fahrenheit conversion section
FWhole = (((Whole * bar) * 18) / 10) + 32;
if ((foo % 10) > 4) {            // round up if needed
++FWhole;
}
}

void printTemp(void) {
lcd.clear();
lcd.setCursor(0,0);
lcd.print(“Temp is: “);
lcd.setCursor(0,1);

if (SignBit) {
lcd.print(“-“);
}
lcd.print(Whole);
lcd.print(” C / “);
lcd.print(FWhole);
lcd.print(” F”);
}

void loop(void) {
getTemp();
printTemp();
delay(1000);
}

Become the Maker you were born to be. Try Arduino Academy for FREE!