Problems with DS18b20 temperature sensor

Comments

• Tracy Allen Posts: 6,667

  2006-12-13 04:51 edited 2006-12-13 04:51

  Walter,
  The DS18B20 is a higher resolution device, so you need to use a different formula. That caught me up too, the first time I used one. Compare the data sheets.
  
  

   ' ----------------------------------------------------------------------------------------------
  ' {$STAMP BS2pe}
  ' {$PBASIC 2.5}
  ' Tracy Allen, EME Systems
  ' DS18B20 (12 bit) program displays temperature, -55 to +125 Celsius +/- 0.1 degree
  ' single one wire device--the skip ROM command can be used.
  degC VAR word
  DO
    OWOUT 0,1,[noparse][[/noparse]$CC, $44]
    DO : OWIN 0,4,[noparse][[/noparse]degC] : LOOP UNTIL degC  ' wait for done
    OWOUT 0,1,[noparse][[/noparse]$CC, $BE]
    OWIN 0,2,[noparse][[/noparse]degC.byte0, degC.byte1]
    DEBUG HOME, REP "-"\degC.bit15, DEC ABS degC/16, ".", DEC1 ABS degC */ 160 , "   " 
  LOOP
  

  
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  Tracy Allen
  www.emesystems.com
• Walter Jann Posts: 5

  2006-12-14 03:48 edited 2006-12-14 03:48

  Thanks Tracy. I really appreciate the help!!
  
  -Walter
• Tracy Allen Posts: 6,667

  2006-12-14 08:32 edited 2006-12-14 08:32

  The older devices (DS1820 and DS18s20) returned 8 bit signed data with 0.5 degree resolution, and you could with a little more trouble get higher resolution by reading the "counts_remaining" register and the "counts_per_degree" register and doing some computations. With the DS18b20 they dispense with the oher registers and simply give you the full 12 bits, signed, with 1/16 degree Celsius resolution. Much nicer to work with!
  
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  Tracy Allen
  www.emesystems.com