DS18B20 Temperature Sensor

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DS18B20 Temperature Sensor

Postby Tim Laren » Thu Apr 05, 2012 7:33 pm

The DS18B20 is a One-Wire device. A One-Wire device is not really a one wire device but a 2 or 3 wire device. After all you always need a ground reference. But it's still real cool and only requires one b pin on your Arduino. If it's local, on your breadboard then you should hook up all three pins, Power, Ground and Data.

Here is the pinout:
Image

The device is an open collector device so it required a pullup resistor on the data line.

    Pin 1 --> Ground
    Pin 2 --> Arduino and a 4.7K to +5V
    Pin 3 --> +5V

You need the OneWire library for this one. It consists of the OneWire.h and OneWire.cpp files. They both go in a folder named OneWire and placed in your library folder in your arduino folder.

OneWire.h:

Code: Select all
#ifndef OneWire_h
#define OneWire_h

#include <inttypes.h>

#if ARDUINO >= 100
#include "Arduino.h"       // for delayMicroseconds, digitalPinToBitMask, etc
#else
#include "WProgram.h"      // for delayMicroseconds
#include "pins_arduino.h"  // for digitalPinToBitMask, etc
#endif

// You can exclude certain features from OneWire.  In theory, this
// might save some space.  In practice, the compiler automatically
// removes unused code (technically, the linker, using -fdata-sections
// and -ffunction-sections when compiling, and Wl,--gc-sections
// when linking), so most of these will not result in any code size
// reduction.  Well, unless you try to use the missing features
// and redesign your program to not need them!  ONEWIRE_CRC8_TABLE
// is the exception, because it selects a fast but large algorithm
// or a small but slow algorithm.

// you can exclude onewire_search by defining that to 0
#ifndef ONEWIRE_SEARCH
#define ONEWIRE_SEARCH 1
#endif

// You can exclude CRC checks altogether by defining this to 0
#ifndef ONEWIRE_CRC
#define ONEWIRE_CRC 1
#endif

// Select the table-lookup method of computing the 8-bit CRC
// by setting this to 1.  The lookup table enlarges code size by
// about 250 bytes.  It does NOT consume RAM (but did in very
// old versions of OneWire).  If you disable this, a slower
// but very compact algorithm is used.
#ifndef ONEWIRE_CRC8_TABLE
#define ONEWIRE_CRC8_TABLE 1
#endif

// You can allow 16-bit CRC checks by defining this to 1
// (Note that ONEWIRE_CRC must also be 1.)
#ifndef ONEWIRE_CRC16
#define ONEWIRE_CRC16 1
#endif

#define FALSE 0
#define TRUE  1

// Platform specific I/O definitions

#if defined(__AVR__)
#define PIN_TO_BASEREG(pin)             (portInputRegister(digitalPinToPort(pin)))
#define PIN_TO_BITMASK(pin)             (digitalPinToBitMask(pin))
#define IO_REG_TYPE uint8_t
#define IO_REG_ASM asm("r30")
#define DIRECT_READ(base, mask)         (((*(base)) & (mask)) ? 1 : 0)
#define DIRECT_MODE_INPUT(base, mask)   ((*(base+1)) &= ~(mask))
#define DIRECT_MODE_OUTPUT(base, mask)  ((*(base+1)) |= (mask))
#define DIRECT_WRITE_LOW(base, mask)    ((*(base+2)) &= ~(mask))
#define DIRECT_WRITE_HIGH(base, mask)   ((*(base+2)) |= (mask))

#elif defined(__PIC32MX__)
#include <plib.h>  // is this necessary?
#define PIN_TO_BASEREG(pin)             (portModeRegister(digitalPinToPort(pin)))
#define PIN_TO_BITMASK(pin)             (digitalPinToBitMask(pin))
#define IO_REG_TYPE uint32_t
#define IO_REG_ASM
#define DIRECT_READ(base, mask)         (((*(base+4)) & (mask)) ? 1 : 0)  //PORTX + 0x10
#define DIRECT_MODE_INPUT(base, mask)   ((*(base+2)) = (mask))            //TRISXSET + 0x08
#define DIRECT_MODE_OUTPUT(base, mask)  ((*(base+1)) = (mask))            //TRISXCLR + 0x04
#define DIRECT_WRITE_LOW(base, mask)    ((*(base+8+1)) = (mask))          //LATXCLR  + 0x24
#define DIRECT_WRITE_HIGH(base, mask)   ((*(base+8+2)) = (mask))          //LATXSET + 0x28

#else
#error "Please define I/O register types here"
#endif


class OneWire
{
  private:
    IO_REG_TYPE bitmask;
    volatile IO_REG_TYPE *baseReg;

#if ONEWIRE_SEARCH
    // global search state
    unsigned char ROM_NO[8];
    uint8_t LastDiscrepancy;
    uint8_t LastFamilyDiscrepancy;
    uint8_t LastDeviceFlag;
#endif

  public:
    OneWire( uint8_t pin);

    // Perform a 1-Wire reset cycle. Returns 1 if a device responds
    // with a presence pulse.  Returns 0 if there is no device or the
    // bus is shorted or otherwise held low for more than 250uS
    uint8_t reset(void);

    // Issue a 1-Wire rom select command, you do the reset first.
    void select( uint8_t rom[8]);

    // Issue a 1-Wire rom skip command, to address all on bus.
    void skip(void);

    // Write a byte. If 'power' is one then the wire is held high at
    // the end for parasitically powered devices. You are responsible
    // for eventually depowering it by calling depower() or doing
    // another read or write.
    void write(uint8_t v, uint8_t power = 0);

    void write_bytes(const uint8_t *buf, uint16_t count, bool power = 0);

    // Read a byte.
    uint8_t read(void);

    void read_bytes(uint8_t *buf, uint16_t count);

    // Write a bit. The bus is always left powered at the end, see
    // note in write() about that.
    void write_bit(uint8_t v);

    // Read a bit.
    uint8_t read_bit(void);

    // Stop forcing power onto the bus. You only need to do this if
    // you used the 'power' flag to write() or used a write_bit() call
    // and aren't about to do another read or write. You would rather
    // not leave this powered if you don't have to, just in case
    // someone shorts your bus.
    void depower(void);

#if ONEWIRE_SEARCH
    // Clear the search state so that if will start from the beginning again.
    void reset_search();

    // Look for the next device. Returns 1 if a new address has been
    // returned. A zero might mean that the bus is shorted, there are
    // no devices, or you have already retrieved all of them.  It
    // might be a good idea to check the CRC to make sure you didn't
    // get garbage.  The order is deterministic. You will always get
    // the same devices in the same order.
    uint8_t search(uint8_t *newAddr);
#endif

#if ONEWIRE_CRC
    // Compute a Dallas Semiconductor 8 bit CRC, these are used in the
    // ROM and scratchpad registers.
    static uint8_t crc8( uint8_t *addr, uint8_t len);

#if ONEWIRE_CRC16
    // Compute the 1-Wire CRC16 and compare it against the received CRC.
    // Example usage (reading a DS2408):
    //    // Put everything in a buffer so we can compute the CRC easily.
    //    uint8_t buf[13];
    //    buf[0] = 0xF0;    // Read PIO Registers
    //    buf[1] = 0x88;    // LSB address
    //    buf[2] = 0x00;    // MSB address
    //    WriteBytes(net, buf, 3);    // Write 3 cmd bytes
    //    ReadBytes(net, buf+3, 10);  // Read 6 data bytes, 2 0xFF, 2 CRC16
    //    if (!CheckCRC16(buf, 11, &buf[11])) {
    //        // Handle error.
    //    }     
    //         
    // @param input - Array of bytes to checksum.
    // @param len - How many bytes to use.
    // @param inverted_crc - The two CRC16 bytes in the received data.
    //                       This should just point into the received data,
    //                       *not* at a 16-bit integer.
    // @return True, iff the CRC matches.
    static bool check_crc16(uint8_t* input, uint16_t len, uint8_t* inverted_crc);

    // Compute a Dallas Semiconductor 16 bit CRC.  This is required to check
    // the integrity of data received from many 1-Wire devices.  Note that the
    // CRC computed here is *not* what you'll get from the 1-Wire network,
    // for two reasons:
    //   1) The CRC is transmitted bitwise inverted.
    //   2) Depending on the endian-ness of your processor, the binary
    //      representation of the two-byte return value may have a different
    //      byte order than the two bytes you get from 1-Wire.
    // @param input - Array of bytes to checksum.
    // @param len - How many bytes to use.
    // @return The CRC16, as defined by Dallas Semiconductor.
    static uint16_t crc16(uint8_t* input, uint16_t len);
#endif
#endif
};

#endif


OneWire.cpp:
Code: Select all
/*
Copyright (c) 2007, Jim Studt  (original old version - many contributors since)

The latest version of this library may be found at:
  http://www.pjrc.com/teensy/td_libs_OneWire.html

Version 2.1:
  Arduino 1.0 compatibility, Paul Stoffregen
  Improve temperature example, Paul Stoffregen
  DS250x_PROM example, Guillermo Lovato
  PIC32 (chipKit) compatibility, Jason Dangel, dangel.jason AT gmail.com
  Improvements from Glenn Trewitt:
  - crc16() now works
  - check_crc16() does all of calculation/checking work.
  - Added read_bytes() and write_bytes(), to reduce tedious loops.
  - Added ds2408 example.
  Delete very old, out-of-date readme file (info is here)

Version 2.0: Modifications by Paul Stoffregen, January 2010:
http://www.pjrc.com/teensy/td_libs_OneWire.html
  Search fix from Robin James
    http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1238032295/27#27
  Use direct optimized I/O in all cases
  Disable interrupts during timing critical sections
    (this solves many random communication errors)
  Disable interrupts during read-modify-write I/O
  Reduce RAM consumption by eliminating unnecessary
    variables and trimming many to 8 bits
  Optimize both crc8 - table version moved to flash

Modified to work with larger numbers of devices - avoids loop.
Tested in Arduino 11 alpha with 12 sensors.
26 Sept 2008 -- Robin James
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1238032295/27#27

Updated to work with arduino-0008 and to include skip() as of
2007/07/06. --RJL20

Modified to calculate the 8-bit CRC directly, avoiding the need for
the 256-byte lookup table to be loaded in RAM.  Tested in arduino-0010
-- Tom Pollard, Jan 23, 2008

Jim Studt's original library was modified by Josh Larios.

Tom Pollard, pollard@alum.mit.edu, contributed around May 20, 2008

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Much of the code was inspired by Derek Yerger's code, though I don't
think much of that remains.  In any event that was..
    (copyleft) 2006 by Derek Yerger - Free to distribute freely.

The CRC code was excerpted and inspired by the Dallas Semiconductor
sample code bearing this copyright.
//---------------------------------------------------------------------------
// Copyright (C) 2000 Dallas Semiconductor Corporation, All Rights Reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY,  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
// IN NO EVENT SHALL DALLAS SEMICONDUCTOR BE LIABLE FOR ANY CLAIM, DAMAGES
// OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
//
// Except as contained in this notice, the name of Dallas Semiconductor
// shall not be used except as stated in the Dallas Semiconductor
// Branding Policy.
//--------------------------------------------------------------------------
*/

#include "OneWire.h"


OneWire::OneWire(uint8_t pin)
{
   pinMode(pin, INPUT);
   bitmask = PIN_TO_BITMASK(pin);
   baseReg = PIN_TO_BASEREG(pin);
#if ONEWIRE_SEARCH
   reset_search();
#endif
}


// Perform the onewire reset function.  We will wait up to 250uS for
// the bus to come high, if it doesn't then it is broken or shorted
// and we return a 0;
//
// Returns 1 if a device asserted a presence pulse, 0 otherwise.
//
uint8_t OneWire::reset(void)
{
   IO_REG_TYPE mask = bitmask;
   volatile IO_REG_TYPE *reg IO_REG_ASM = baseReg;
   uint8_t r;
   uint8_t retries = 125;

   noInterrupts();
   DIRECT_MODE_INPUT(reg, mask);
   interrupts();
   // wait until the wire is high... just in case
   do {
      if (--retries == 0) return 0;
      delayMicroseconds(2);
   } while ( !DIRECT_READ(reg, mask));

   noInterrupts();
   DIRECT_WRITE_LOW(reg, mask);
   DIRECT_MODE_OUTPUT(reg, mask);   // drive output low
   interrupts();
   delayMicroseconds(500);
   noInterrupts();
   DIRECT_MODE_INPUT(reg, mask);   // allow it to float
   delayMicroseconds(80);
   r = !DIRECT_READ(reg, mask);
   interrupts();
   delayMicroseconds(420);
   return r;
}

//
// Write a bit. Port and bit is used to cut lookup time and provide
// more certain timing.
//
void OneWire::write_bit(uint8_t v)
{
   IO_REG_TYPE mask=bitmask;
   volatile IO_REG_TYPE *reg IO_REG_ASM = baseReg;

   if (v & 1) {
      noInterrupts();
      DIRECT_WRITE_LOW(reg, mask);
      DIRECT_MODE_OUTPUT(reg, mask);   // drive output low
      delayMicroseconds(10);
      DIRECT_WRITE_HIGH(reg, mask);   // drive output high
      interrupts();
      delayMicroseconds(55);
   } else {
      noInterrupts();
      DIRECT_WRITE_LOW(reg, mask);
      DIRECT_MODE_OUTPUT(reg, mask);   // drive output low
      delayMicroseconds(65);
      DIRECT_WRITE_HIGH(reg, mask);   // drive output high
      interrupts();
      delayMicroseconds(5);
   }
}

//
// Read a bit. Port and bit is used to cut lookup time and provide
// more certain timing.
//
uint8_t OneWire::read_bit(void)
{
   IO_REG_TYPE mask=bitmask;
   volatile IO_REG_TYPE *reg IO_REG_ASM = baseReg;
   uint8_t r;

   noInterrupts();
   DIRECT_MODE_OUTPUT(reg, mask);
   DIRECT_WRITE_LOW(reg, mask);
   delayMicroseconds(3);
   DIRECT_MODE_INPUT(reg, mask);   // let pin float, pull up will raise
   delayMicroseconds(10);
   r = DIRECT_READ(reg, mask);
   interrupts();
   delayMicroseconds(53);
   return r;
}

//
// Write a byte. The writing code uses the active drivers to raise the
// pin high, if you need power after the write (e.g. DS18S20 in
// parasite power mode) then set 'power' to 1, otherwise the pin will
// go tri-state at the end of the write to avoid heating in a short or
// other mishap.
//
void OneWire::write(uint8_t v, uint8_t power /* = 0 */) {
    uint8_t bitMask;

    for (bitMask = 0x01; bitMask; bitMask <<= 1) {
   OneWire::write_bit( (bitMask & v)?1:0);
    }
    if ( !power) {
   noInterrupts();
   DIRECT_MODE_INPUT(baseReg, bitmask);
   DIRECT_WRITE_LOW(baseReg, bitmask);
   interrupts();
    }
}

void OneWire::write_bytes(const uint8_t *buf, uint16_t count, bool power /* = 0 */) {
  for (uint16_t i = 0 ; i < count ; i++)
    write(buf[i]);
  if (!power) {
    noInterrupts();
    DIRECT_MODE_INPUT(baseReg, bitmask);
    DIRECT_WRITE_LOW(baseReg, bitmask);
    interrupts();
  }
}

//
// Read a byte
//
uint8_t OneWire::read() {
    uint8_t bitMask;
    uint8_t r = 0;

    for (bitMask = 0x01; bitMask; bitMask <<= 1) {
   if ( OneWire::read_bit()) r |= bitMask;
    }
    return r;
}

void OneWire::read_bytes(uint8_t *buf, uint16_t count) {
  for (uint16_t i = 0 ; i < count ; i++)
    buf[i] = read();
}

//
// Do a ROM select
//
void OneWire::select( uint8_t rom[8])
{
    int i;

    write(0x55);           // Choose ROM

    for( i = 0; i < 8; i++) write(rom[i]);
}

//
// Do a ROM skip
//
void OneWire::skip()
{
    write(0xCC);           // Skip ROM
}

void OneWire::depower()
{
   noInterrupts();
   DIRECT_MODE_INPUT(baseReg, bitmask);
   interrupts();
}

#if ONEWIRE_SEARCH

//
// You need to use this function to start a search again from the beginning.
// You do not need to do it for the first search, though you could.
//
void OneWire::reset_search()
  {
  // reset the search state
  LastDiscrepancy = 0;
  LastDeviceFlag = FALSE;
  LastFamilyDiscrepancy = 0;
  for(int i = 7; ; i--)
    {
    ROM_NO[i] = 0;
    if ( i == 0) break;
    }
  }

//
// Perform a search. If this function returns a '1' then it has
// enumerated the next device and you may retrieve the ROM from the
// OneWire::address variable. If there are no devices, no further
// devices, or something horrible happens in the middle of the
// enumeration then a 0 is returned.  If a new device is found then
// its address is copied to newAddr.  Use OneWire::reset_search() to
// start over.
//
// --- Replaced by the one from the Dallas Semiconductor web site ---
//--------------------------------------------------------------------------
// Perform the 1-Wire Search Algorithm on the 1-Wire bus using the existing
// search state.
// Return TRUE  : device found, ROM number in ROM_NO buffer
//        FALSE : device not found, end of search
//
uint8_t OneWire::search(uint8_t *newAddr)
{
   uint8_t id_bit_number;
   uint8_t last_zero, rom_byte_number, search_result;
   uint8_t id_bit, cmp_id_bit;

   unsigned char rom_byte_mask, search_direction;

   // initialize for search
   id_bit_number = 1;
   last_zero = 0;
   rom_byte_number = 0;
   rom_byte_mask = 1;
   search_result = 0;

   // if the last call was not the last one
   if (!LastDeviceFlag)
   {
      // 1-Wire reset
      if (!reset())
      {
         // reset the search
         LastDiscrepancy = 0;
         LastDeviceFlag = FALSE;
         LastFamilyDiscrepancy = 0;
         return FALSE;
      }

      // issue the search command
      write(0xF0);

      // loop to do the search
      do
      {
         // read a bit and its complement
         id_bit = read_bit();
         cmp_id_bit = read_bit();

         // check for no devices on 1-wire
         if ((id_bit == 1) && (cmp_id_bit == 1))
            break;
         else
         {
            // all devices coupled have 0 or 1
            if (id_bit != cmp_id_bit)
               search_direction = id_bit;  // bit write value for search
            else
            {
               // if this discrepancy if before the Last Discrepancy
               // on a previous next then pick the same as last time
               if (id_bit_number < LastDiscrepancy)
                  search_direction = ((ROM_NO[rom_byte_number] & rom_byte_mask) > 0);
               else
                  // if equal to last pick 1, if not then pick 0
                  search_direction = (id_bit_number == LastDiscrepancy);

               // if 0 was picked then record its position in LastZero
               if (search_direction == 0)
               {
                  last_zero = id_bit_number;

                  // check for Last discrepancy in family
                  if (last_zero < 9)
                     LastFamilyDiscrepancy = last_zero;
               }
            }

            // set or clear the bit in the ROM byte rom_byte_number
            // with mask rom_byte_mask
            if (search_direction == 1)
              ROM_NO[rom_byte_number] |= rom_byte_mask;
            else
              ROM_NO[rom_byte_number] &= ~rom_byte_mask;

            // serial number search direction write bit
            write_bit(search_direction);

            // increment the byte counter id_bit_number
            // and shift the mask rom_byte_mask
            id_bit_number++;
            rom_byte_mask <<= 1;

            // if the mask is 0 then go to new SerialNum byte rom_byte_number and reset mask
            if (rom_byte_mask == 0)
            {
                rom_byte_number++;
                rom_byte_mask = 1;
            }
         }
      }
      while(rom_byte_number < 8);  // loop until through all ROM bytes 0-7

      // if the search was successful then
      if (!(id_bit_number < 65))
      {
         // search successful so set LastDiscrepancy,LastDeviceFlag,search_result
         LastDiscrepancy = last_zero;

         // check for last device
         if (LastDiscrepancy == 0)
            LastDeviceFlag = TRUE;

         search_result = TRUE;
      }
   }

   // if no device found then reset counters so next 'search' will be like a first
   if (!search_result || !ROM_NO[0])
   {
      LastDiscrepancy = 0;
      LastDeviceFlag = FALSE;
      LastFamilyDiscrepancy = 0;
      search_result = FALSE;
   }
   for (int i = 0; i < 8; i++) newAddr[i] = ROM_NO[i];
   return search_result;
  }

#endif

#if ONEWIRE_CRC
// The 1-Wire CRC scheme is described in Maxim Application Note 27:
// "Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products"
//

#if ONEWIRE_CRC8_TABLE
// This table comes from Dallas sample code where it is freely reusable,
// though Copyright (C) 2000 Dallas Semiconductor Corporation
static const uint8_t PROGMEM dscrc_table[] = {
      0, 94,188,226, 97, 63,221,131,194,156,126, 32,163,253, 31, 65,
    157,195, 33,127,252,162, 64, 30, 95,  1,227,189, 62, 96,130,220,
     35,125,159,193, 66, 28,254,160,225,191, 93,  3,128,222, 60, 98,
    190,224,  2, 92,223,129, 99, 61,124, 34,192,158, 29, 67,161,255,
     70, 24,250,164, 39,121,155,197,132,218, 56,102,229,187, 89,  7,
    219,133,103, 57,186,228,  6, 88, 25, 71,165,251,120, 38,196,154,
    101, 59,217,135,  4, 90,184,230,167,249, 27, 69,198,152,122, 36,
    248,166, 68, 26,153,199, 37,123, 58,100,134,216, 91,  5,231,185,
    140,210, 48,110,237,179, 81, 15, 78, 16,242,172, 47,113,147,205,
     17, 79,173,243,112, 46,204,146,211,141,111, 49,178,236, 14, 80,
    175,241, 19, 77,206,144,114, 44,109, 51,209,143, 12, 82,176,238,
     50,108,142,208, 83, 13,239,177,240,174, 76, 18,145,207, 45,115,
    202,148,118, 40,171,245, 23, 73,  8, 86,180,234,105, 55,213,139,
     87,  9,235,181, 54,104,138,212,149,203, 41,119,244,170, 72, 22,
    233,183, 85, 11,136,214, 52,106, 43,117,151,201, 74, 20,246,168,
    116, 42,200,150, 21, 75,169,247,182,232, 10, 84,215,137,107, 53};

//
// Compute a Dallas Semiconductor 8 bit CRC. These show up in the ROM
// and the registers.  (note: this might better be done without to
// table, it would probably be smaller and certainly fast enough
// compared to all those delayMicrosecond() calls.  But I got
// confused, so I use this table from the examples.)
//
uint8_t OneWire::crc8( uint8_t *addr, uint8_t len)
{
   uint8_t crc = 0;

   while (len--) {
      crc = pgm_read_byte(dscrc_table + (crc ^ *addr++));
   }
   return crc;
}
#else
//
// Compute a Dallas Semiconductor 8 bit CRC directly.
// this is much slower, but much smaller, than the lookup table.
//
uint8_t OneWire::crc8( uint8_t *addr, uint8_t len)
{
   uint8_t crc = 0;
   
   while (len--) {
      uint8_t inbyte = *addr++;
      for (uint8_t i = 8; i; i--) {
         uint8_t mix = (crc ^ inbyte) & 0x01;
         crc >>= 1;
         if (mix) crc ^= 0x8C;
         inbyte >>= 1;
      }
   }
   return crc;
}
#endif

#if ONEWIRE_CRC16
bool OneWire::check_crc16(uint8_t* input, uint16_t len, uint8_t* inverted_crc)
{
    uint16_t crc = ~crc16(input, len);
    return (crc & 0xFF) == inverted_crc[0] && (crc >> 8) == inverted_crc[1];
}

uint16_t OneWire::crc16(uint8_t* input, uint16_t len)
{
    static const uint8_t oddparity[16] =
        { 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0 };
    uint16_t crc = 0;    // Starting seed is zero.

    for (uint16_t i = 0 ; i < len ; i++) {
      // Even though we're just copying a byte from the input,
      // we'll be doing 16-bit computation with it.
      uint16_t cdata = input[i];
      cdata = (cdata ^ (crc & 0xff)) & 0xff;
      crc >>= 8;

      if (oddparity[cdata & 0x0F] ^ oddparity[cdata >> 4])
          crc ^= 0xC001;

      cdata <<= 6;
      crc ^= cdata;
      cdata <<= 1;
      crc ^= cdata;
    }
    return crc;
}
#endif

#endif


Here is the example sketch:

Code: Select all
#include <OneWire.h>

// OneWire DS18S20, DS18B20, DS1822 Temperature Example
//
// http://www.pjrc.com/teensy/td_libs_OneWire.html
//
// The DallasTemperature library can do all this work for you!
// http://milesburton.com/Dallas_Temperature_Control_Library

OneWire  ds(10);  // on pin 10

void setup(void) {
  Serial.begin(9600);
}

void loop(void) {
  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius, fahrenheit;
 
  if ( !ds.search(addr)) {
    Serial.println("No more addresses.");
    Serial.println();
    ds.reset_search();
    delay(250);
    return;
  }
 
  Serial.print("ROM =");
  for( i = 0; i < 8; i++) {
    Serial.write(' ');
    Serial.print(addr[i], HEX);
  }

  if (OneWire::crc8(addr, 7) != addr[7]) {
      Serial.println("CRC is not valid!");
      return;
  }
  Serial.println();
 
  // the first ROM byte indicates which chip
  switch (addr[0]) {
    case 0x10:
      Serial.println("  Chip = DS18S20");  // or old DS1820
      type_s = 1;
      break;
    case 0x28:
      Serial.println("  Chip = DS18B20");
      type_s = 0;
      break;
    case 0x22:
      Serial.println("  Chip = DS1822");
      type_s = 0;
      break;
    default:
      Serial.println("Device is not a DS18x20 family device.");
      return;
  }

  ds.reset();
  ds.select(addr);
  ds.write(0x44,1);         // start conversion, with parasite power on at the end
 
  delay(1000);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.
 
  present = ds.reset();
  ds.select(addr);   
  ds.write(0xBE);         // Read Scratchpad

  Serial.print("  Data = ");
  Serial.print(present,HEX);
  Serial.print(" ");
  for ( i = 0; i < 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
    Serial.print(data[i], HEX);
    Serial.print(" ");
  }
  Serial.print(" CRC=");
  Serial.print(OneWire::crc8(data, 8), HEX);
  Serial.println();

  // convert the data to actual temperature

  unsigned int raw = (data[1] << 8) | data[0];
  if (type_s) {
    raw = raw << 3; // 9 bit resolution default
    if (data[7] == 0x10) {
      // count remain gives full 12 bit resolution
      raw = (raw & 0xFFF0) + 12 - data[6];
    }
  } else {
    byte cfg = (data[4] & 0x60);
    if (cfg == 0x00) raw = raw << 3;  // 9 bit resolution, 93.75 ms
    else if (cfg == 0x20) raw = raw << 2; // 10 bit res, 187.5 ms
    else if (cfg == 0x40) raw = raw << 1; // 11 bit res, 375 ms
    // default is 12 bit resolution, 750 ms conversion time
  }
  celsius = (float)raw / 16.0;
  fahrenheit = celsius * 1.8 + 32.0;
  Serial.print("  Temperature = ");
  Serial.print(celsius);
  Serial.print(" Celsius, ");
  Serial.print(fahrenheit);
  Serial.println(" Fahrenheit");
}


Here is all the OneWire code with other examples also. Unzip into your library folder.
OneWire.zip
Full OneWire library.
(14.38 KiB) Downloaded 511 times
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Tim Laren
Site Admin
 
Posts: 137
Joined: Thu Mar 04, 2010 8:25 pm

DS18B20 Temparture Sensor

Postby Tim Laren » Thu Apr 05, 2012 7:45 pm

I also made up a LCD version for all of you who have an LCD display or shield for your Arduino. You need to install the library OneWire from the original post before uploading this sketch as it requires the OneWire library to compile.

Use the same wiring as in the first example.

Here is the sketch:

Code: Select all
// include the library code:
#include <LiquidCrystal.h>
#include <OneWire.h>

OneWire  ds(10);  // on pin 10

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup(){
  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.println("DS18B20 Sensor ");
}

void loop(){
  DS18b20();
  ds.reset_search();
  delay(250);
}

void DS18b20(void) {
  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius, fahrenheit;
 
  lcd.setCursor(0,1);

  if(ds.search(addr)) {
    if (OneWire::crc8(addr, 7) != addr[7]) {
      lcd.print("CRC err");
      return;
    }
 
    // the first ROM byte indicates which chip
    switch (addr[0]) {
      case 0x10:
        type_s = 1;
        break;
      case 0x28:
        type_s = 0;
        break;
      case 0x22:
        type_s = 0;
        break;
      default:
        return;
    }

    ds.reset();
    ds.select(addr);
    ds.write(0x44,1);         // start conversion, with parasite power on at the end
 
    delay(1000);     // maybe 750ms is enough, maybe not
    // we might do a ds.depower() here, but the reset will take care of it.
 
    present = ds.reset();
    ds.select(addr);   
    ds.write(0xBE);         // Read Scratchpad

    for ( i = 0; i < 9; i++) {           // we need 9 bytes
      data[i] = ds.read();
    }
    unsigned int raw = (data[1] << 8) | data[0];
    if (type_s) {
      raw = raw << 3; // 9 bit resolution default
      if (data[7] == 0x10) {
        // count remain gives full 12 bit resolution
        raw = (raw & 0xFFF0) + 12 - data[6];
      }
    } else {
      byte cfg = (data[4] & 0x60);
      if (cfg == 0x00) raw = raw << 3;  // 9 bit resolution, 93.75 ms
      else if (cfg == 0x20) raw = raw << 2; // 10 bit res, 187.5 ms
      else if (cfg == 0x40) raw = raw << 1; // 11 bit res, 375 ms
      // default is 12 bit resolution, 750 ms conversion time
    }
    celsius = (float)raw / 16.0;
    fahrenheit = celsius * 1.8 + 32.0;
    lcd.print(fahrenheit);
  }
}


Here is the code zipped up for you:
DS18B20_LCD.zip
DS18B20 with LCD Display
(1.25 KiB) Downloaded 475 times

Hope you come up with some cool projects for this sensor. If you do, please talk about them here with everyone.
Image
Tim Laren
Site Admin
 
Posts: 137
Joined: Thu Mar 04, 2010 8:25 pm

DS18B20 Temperature Sensor

Postby Adam41kgance » Wed Sep 12, 2018 4:37 am

Hi
Can we consider the embedded temperature sensor as an ambient temperature measurement?
Or is it strongly biaised by the component temperature?
Thanks
francois
Adam41kgance
 
Posts: 3
Joined: Wed Sep 05, 2018 8:21 am
Location: USA

Re: DS18B20 Temperature Sensor

Postby Tim Laren » Wed Sep 12, 2018 10:51 am

Not sure of the question?
The temperature of the device is what is measured. It is not an IR sensor.
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Tim Laren
Site Admin
 
Posts: 137
Joined: Thu Mar 04, 2010 8:25 pm


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