DS1921-Thermochron(3)

NAME
DS1921 - Thermochron temperature logging iButton.

SYNOPSIS
Temperature logging iButton.

21 [.]XXXXXXXXXXXX[XX][/[
about/[measuring| resolution| samples| templow| temphigh| version] |
clock/[date| running| udate] |
histotgram/[counts[0-62|ALL]| gap| temperature[counts[0-62|ALL]] |
log[date[0-2047|ALL]| elements| temperature[0-2047|ALL]| udate[0-2047|ALL]] |
memory |
mission/[date| delay| easystart| frequency| rollover| running| samples| sampling| udate] |
overtemp/[date[0-11|ALL]| elements| end[0-11|ALL]| count[0-11|ALL]| temperature[0-11|ALL]| udate[0-11|ALL]] |
pages/page.[0-15|ALL] |
temperature |
undertemp/[date[0-11|ALL]| elements|end[0-11|ALL]| count[0-11|ALL]| temperature[0-11|ALL]| udate[0-11|ALL]] | ]]

FAMILY CODE

21

SPECIAL PROPERTIES

  about/measuring
read-only, yes-no
Is this DS1921 currently measuring a temperature?

  about/resolution
read-only, floating point
What is the resolution of the temperature measurments (in the current temperature scale).

  about/samples
read-only, unsigned integer
How many total temperature measurements has this DS1921 performed?

  about/temphigh
read-only, floating point
Highest temperature this DS1921 can measure (in the current temperature scale).

  about/templow
read-only, floating point
Lowest temperature this DS1921 can measure (in the current temperature scale).

  about/version
read-only, ascii
Specific version of this DS1921.

  clock/date
read-write, ascii
26 character date representation of the internal time stored in this DS1921. Increments once per second while clock/running
Setting date to a null string will put the current system time.
Accepted date formats are:
  Sat[urday] March 12 12:23:59 2001
  Apr[il] 4 9:34:56 2002
  3/23/04 23:34:57
  current locale setting (your system's format)

  clock/running
read-write, yes-no
Whether the internal clock is running. This can be explicitly set, and is automatically started by setting clock/date or clock/udate or by starting a mission with mission/easystart or mission/frequency

The main reason to stop the clock is to conserve the internal battery. The clock cannot be stopped during a mission, and the clock is essential for a mission.

  clock/udate
read-write, unsigned integer
A numeric representation of clock/date
The number of seconds in UNIX time (since Jan 1, 1970).

  histogram/counts.0 ... histogram/counts.62 histogram/counts.ALL
read-only, unsigned integer
The number of samples in the current mission whose temperature fell within the histogram/temperature to histogram/temperature+histogram/gap range.

  histogram/elements
read-only, unsigned integer
The number of bins in the histogram. Always 63.

  histogram/gap
read-only, floating point
The size of the histogram bin. Depends on the Thermochron version ( about/version ) and is usually 4 times about/resolution

Given in the current temperatature scale.

  histogram/temperature.0 ... histogram/temperature.62 histogram/temperature.ALL
read-only, floating point
Lower limit of the temperature range for the corresponding histogram bin. In the current temperature scale.

  log/date.0 ... log/date.2047 log/date.ALL
read-only, ascii
Date that the corresponding log/temperature was taken, in ascii format. (See clock/date for more on the format). The number of valid entries is actually log/elements since the log may not be full.

mission/samples gives the total number of samples that have been taken but there is only room in the log for 2048 entries. Once the log is full, mission/rollover determines the Thermochron's behavior.

If mission/rollover is false(0), the log will hold the first 2048 samples and log/date.0 will always be the same as mission/date

If mission/rollover is true (1) then the log will hold the last 2048 samples and the entries will be shifted down with each new sample.

Note the OWFS code "untwists" the rollover behavior. The data will always be a linear array of earliest to latest.

ALL is the all data elements comma separated.

  log/elements
read-only, unsigned integer
Number of valid entries in the log. OWFS offers the full 2048 values in the log memory, but not that many samples may yet have been taken. log/elements will range from 0 to 2048 and always be less than or equal to mission/samples

  log/temperature.0 ... log/temperature.2047 log/temperature.ALL
read-write, floating point
The temperature readings (in the current temperature scale) that correspond to the log/date sample. See log/date for details on the indexing scheme and rollover behavior.

  log/udate.0 ... log/udate.2047 log/udate.ALL
read-write, unsigned integer
A numeric representation of log/date
The number of seconds in UNIX time (since Jan 1, 1970).

  memory
read-write, binary
User available storage space. 512 bytes. Can also be accessed as 16 pages of 32 bytes with the pages/page.x properties.

  overtemp/count.0 ... overtemp/count.11 overtemp/count.ALL

  undertemp/count.0 ... undertemp/count.11 undertemp/count.ALL
read-only, unsigned integer
Number of sampling periods that the Thermochron stayed out of range during a mission. Each sampling period is mission/frequency minutes long.

  overtemp/end.0 ... overtemp/end.11 overtemp/end.ALL

  undertemp/end.0 ... undertemp/end.11 undertemp/end.ALL
read-only, ascii
End of time that the Thermochron went out of range during the current mission. See clock/date for format.

Each period can be up to 255 samples in length, and span the time overtemp/date to overtemp/end ( or undertemp/date to undertemp/end ).

  overtemp/date.0 ... overtemp/date.11 overtemp/date.ALL

  undertemp/date.0 ... undertemp/date.11 undertemp/date.ALL
read-only, ascii
Time that the Thermochron went out of range during the current mission. See clock/date for format.

  overtemp/elements

  undertemp/elements
read-only, unsigned integer
Number of entries (0 to 12) in the overtemp or undertemp array.

  overtemp/temperature

  undertemp/temperature
read-write, floating point
Temperature limit to trigger alarm and error log. overtemp/temperature gives upper limit and undertemp/temperature gives lower limit.
In current temperature scale.

  overtemp/udate.0 ... overtemp/udate.11 overtemp/udate.ALL

  undertemp/udate.0 ... undertemp/udate.11 undertemp/udate.ALL
read-only, unsigned integer
A numeric representation of overtemp/date or undertemp/date
The number of seconds in UNIX time (since Jan 1, 1970).

  pages/page.0 ... pages/page.15 pages/page.ALL
read-write, binary
Memory is split into 16 pages of 32 bytes each. User available. The log memory, register banks and histogram data area are all separate from this memory area.
ALL is an aggregate of the pages. Each page is accessed sequentially.

  temperature
read-only, floating point
Last temperature explicitly requested. Only available when the mission is not in progress. Value returned in in the current temperature scale.

STANDARD PROPERTIES

ALARMS
None.

DESCRIPTION

  DS1921 Thermochron
The DS1921 (3) is an iButton device with many intriguing functions. Essentially it monitors temperature, giving both a log of readings, and a histogram of temperature ranges. The specification is somewhat complex, but OWFS hides many of the implementation details.

While on a mission the DS1921 (3) records temperature readings in a 2048-sample log and adds them to a 62-bin histogram.

ADDRESSING

DATASHEET
http://pdfserv.maxim-ic.com/en/ds/DS2438.pdf
http://pdfserv.maxim-ic.com/en/an/humsensor.pdf

SEE ALSO

AVAILABILITY
http://www.owfs.org

AUTHOR
Paul Alfille (paul.alfille@gmail.com)