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Temperature measurements

Temperature measurement is one of the most popular 1-wire features.

  • Device choices

    • Thermochrons

      The DS1921, DS1922 and DS1923 not only read temperature, they store repeated measurements in stand-alone opertion. Internal battery operated.

    • Thermometers

      Includes the DS18S20, DS18B20, DS1822, DS1825 and DS28EA00. These chips differ in accuracy, cost and speed. All support parasytic temperature conversion.

    • Thermostat

      The DS1821 is a quasi 1-wire device. but supported by OWFS.

    • Battery monitors

      The DS243x, DS2740, DS275x,DS276x, DS277x, DS278x all support temperature measurements as well some voltage and current measurements (and time, memory, switch functions as well). Powered operation.

  • Power requirements

    Temperature measurement tends to be an energy-intensive activity. Some devices, like the DS1921 can measure temperature repeatedly, but require separate power (non-parasytic). Parasytic power measurements (off the data line), are best performed with a "strong pullup" and only a single chip measuring at a time.
    Multiple concurrent measurements can be made with external power. See the "simultaneous" section below.

  • Timing issues

    • Continuous.

      The DS27XX batttery monitors can do continuous temperature measurements. The resolution is 10 bits and the range -40 to 85C.

    • Demand

      Most temperature measurements are done on command. First a "covert temperature" command is sent, and then the measurement is retrieved after some interval.

    • Conversion time

      Chip Bits Range (ºC) Time (ms) Parasytic?
      DS2436 13 -40 to 85 10 ?

      DS2438

      		 13 -55 to 125 10 ?

      DS18S20

      		 9 -55 to 125 1000 yes

      DS18B20 DS1825 DS28EA0

      		 9 -55 to 125 110 yes

      DS18B20 DS1825 DS28EA00

      		 10   200 yes

      DS18B20 DS1825 DS28EA00

      		 11   400 yes

      DS18B20 DS1825 DS28EA00

      		 12   1000 yes
      DS2756 DS276X 10 -40 to 85 220 no  
      DS278X 10 -40 TO 85 440 no        
                 
               

    • Cached values

    • Simultaneous

  • Temperature scale

    By default, values are reported in Celsius. Fahrentheit, Kelvin and Rankine can be selected either from the command line, or under "settings".

    • Command line

      Temperature Scale
      -C --Celsius
      -F --Fahrenheit
      -K --Kelvin
      -R --Rankine

    • Settings

      cat "C" > /1wire/settings/units/temperature_scale # Celsius
      cat "F" > /1wire/settings/units/temperature_scale # Fahrenheit
      cat "K" > /1wire/settings/units/temperature_scale # Kelvin
      cat "R" > /1wire/settings/units/temperature_scale # Rankine

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