18B20_Temerature_Sensor_(Arduino_Compatible)_(SKU__DFR0024) - jimaobian/DFRobotWiki GitHub Wiki

18B20 Temperature Sensor

Introduction

The DS18B20 is a very small thermometer which can be easily hooked into the Arduino MCU through any digital input! It requires very little in the way of additional support, a couple of resistors and some hookup cables and you're set to go.

For more information on the DS18B20 check out http://www.maxim-ic.com/quick_view2.cfm?qv_pk=2812 Maxim-IC.

The Library

This library is derived from some good work by the Arduino community. This library is, for the most part, purely a refactor version of the existing library. I found the original to be somewhat of a pain to implement and, like most Arduino libraries, code-seperation sucks.

The intention of this Library is to build on Jim Studt work and make it quick and easy for beginners to get started.

Limitations

  • The One-Wire library has a nasty look-up table for some associated commands. It isn't directly related to this library but it may cause some problems.

Benefits

  • Simple and easy to use
  • No software limitation to the number of devices you may use

Pin Definition

Temperature Sensor pin definition :

:#Input

:#Power

:#GND

digital input module

Connection Diagram

Digital module connection diagram

Sample Code

#include <OneWire.h>

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);
}

void loop(void) {
  float temperature = getTemp();
  Serial.println(temperature);

  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;

}

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