Working with Dallas DS18S20 and DS18B20 temperature sensors

DS18S20/DS18B20

The DS18S20 and DS18P20 are two temperature sensors from Dallas. They function on a one-wire bus which mean that for communication you need just a single wire.

Code to detect temperature sensors on a one-wire bus

The code for doing this :

#include <OneWire.h>
 
//init the one wire interface on pin 10
OneWire ow(10);
 
void setup(void) {
  Serial.begin(9600);
  lookUpSensors();
}
 
void lookUpSensors(){
  byte address[8];
  int i=0;
  byte ok = 0, tmp = 0;
  //start the search
  Serial.println("--Search started--");
  while (ow.search(address)){
    tmp = 0;
    //0x10 = DS18S20
    if (address[0] == 0x10){
      Serial.print("Device is a DS18S20 : ");
      tmp = 1;
    } else {
      //0x28 = DS18B20
      if (address[0] == 0x28){
        Serial.print("Device is a DS18B20 : ");
        tmp = 1;
      }
    }
    //display the address, if tmp is ok
    if (tmp == 1){
      if (OneWire::crc8(address, 7) != address[7]){
        Serial.println("but it doesn't have a valid CRC!");
      } else {
        //all is ok, display it
        for (i=0;i<8;i++){
          if (address[i] < 9){
            Serial.print("0");
          }
          Serial.print(address[i],HEX);
          if (i<7){
            Serial.print("-");
          }
        }
        Serial.println("");
        ok = 1;
      }
    }//end if tmp
  }//end while
  if (ok == 0){
    Serial.println("No devices were found");
  }
  Serial.println("--Search ended--");
}
 
void loop(void) {
  //do nothing :)
}

and an output sample :

--Search started--
Device is a DS18S20 : 10-1D-30-F9-01-08-00-51
--Search ended--

Read the temperature in Celsius and Fahrenheit degrees

The code for reading the temperature from the temperature sensors :

#include <OneWire.h>
 
//init the one wire interface on pin 10
OneWire  ow(10);
 
//write here the address you receive from the other program
byte sensor[8] = {0x10, 0x1D, 0x30, 0xF9, 0x01, 0x08, 0x00, 0x51};
 
void setup(void) {
  Serial.begin(9600);
}
 
void writeTimeToScratchpad(byte* address){
  //reset the bus
  ow.reset();
  //select our sensor
  ow.select(address);
  //CONVERT T function call (44h) which puts the temperature into the
scratchpad
  ow.write(0x44,1);
  //sleep a second for the write to take place
  delay(1000);
}
 
void readTimeFromScratchpad(byte* address, byte* data){
  //reset the bus
  ow.reset();
  //select our sensor
  ow.select(address);
  //read the scratchpad (BEh)
  ow.write(0xBE);
  for (byte i=0;i<9;i++){
    data[i] = ow.read();
  }
}
 
float getTemperature(byte* address){
  int tr;
  byte data[12];
 
  writeTimeToScratchpad(address);
 
  readTimeFromScratchpad(address,data);
 
  //put in temp all the 8 bits of LSB (least significant byte)
  tr = data[0];
 
  //check for negative temperature
  if (data[1] > 0x80){
    tr = !tr + 1; //two's complement adjustment
    tr = tr * -1; //flip value negative.
  }
 
  //COUNT PER Celsius degree (10h)
  int cpc = data[7];
  //COUNT REMAIN (0Ch)
  int cr = data[6];
 
  //drop bit 0
  tr = tr >> 1;
 
  //calculate the temperature based on this formula :
  //TEMPERATURE = TEMP READ - 0.25 + (COUNT PER Celsius Degree - COUNT REMAIN)
/ (COUNT PER Celsius Degree)
 
  return tr - (float)0.25 + (cpc - cr)/(float)cpc;
}
 
//fahrenheit to celsius conversion
float f2c(float val){
  float aux = val - 32;
  return (aux * 5 / 9);
}
 
//celsius to fahrenheit conversion
float c2f(float val){
  float aux = (val * 9 / 5);
  return (aux + 32);
}
 
void loop(void) {
  float temp;
  float tmp2;
  tmp2 = getTemperature(sensor);
  temp = c2f(tmp2);
 
  Serial.print("Temp = ");
  Serial.print(temp);
  Serial.print(" F or ");
  Serial.print(tmp2);
  Serial.println(" C");
  //wait 30 seconds
  delay(30000);
}

An image of the project

Here is an image of the project :