DS1921 − Thermochron temperature logging iButton.
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]]
| ]]
21
read-only,
yes-no
Is this DS1921 currently measuring a
temperature?
read-only,
floating point
What is the resolution of the temperature measurments
(in the current temperature scale).
read-only,
unsigned integer
How many total temperature measurements has this
DS1921 performed?
read-only,
floating point
Highest temperature this DS1921 can measure (in the
current temperature scale).
read-only,
floating point
Lowest temperature this DS1921 can measure (in the
current temperature scale).
read-only,
ascii
Specific version of this DS1921.
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)
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.
read-write,
unsigned integer
A numeric representation of clock/date
The number of seconds in UNIX time (since Jan 1, 1970).
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.
read-only,
unsigned integer
The number of bins in the histogram. Always 63.
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.
read-only,
floating point
Lower limit of the temperature range for the corresponding
histogram bin. In the current temperature scale.
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.
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
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.
read-write,
unsigned integer
A numeric representation of log/date
The number of seconds in UNIX time (since Jan 1, 1970).
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.
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.
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 ).
read-only,
ascii
Time that the Thermochron went out of range during the
current mission. See clock/date for format.
read-only,
unsigned integer
Number of entries (0 to 12) in the overtemp or
undertemp array.
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.
read-only,
unsigned integer
A numeric representation of overtemp/date or
undertemp/date
The number of seconds in UNIX time (since Jan 1, 1970).
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.
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.
None.
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.
http://pdfserv.maxim-ic.com/en/ds/DS2438.pdf
http://pdfserv.maxim-ic.com/en/an/humsensor.pdf
http://www.owfs.org
Paul Alfille ([email protected])