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DS1921 - Thermochron temperature logging iButton.
Contents
Addressing
All 1-wire devices are factory assigned a unique 64-bit address. This address is of the form:
FamilyCode
8 bits
Address
48 bits
CRC 8 bits
Addressing under OWFS is in hexadecimal, of form:
01.123456789ABC
where 01 is an example 8-bit family code, and 12345678ABC is an example 48 bit address.
The dot is optional, and the CRC code can included. If included, it must be correct.
Alarms
None.
Availability
Datasheet
Description
1-Wire1-wire is a wiring protocol and series of devices designed and manufactured by Dallas Semiconductor, Inc.
The bus is a low-power low-speed low-connector scheme where the data line can also provide power.
Each device is uniquely and unalterably numbered during manufacture. There are a wide variety of devices,
including memory, sensors (humidity, temperature, voltage, contact, current), switches, timers and data
loggers. More complex devices (like thermocouple sensors) can be built with these basic devices. There
are also 1-wire devices that have encryption included.
The 1-wire scheme uses a single busmaster and multiple slaves on the same wire. The bus master initiates
all communication. The slaves can be individually discovered and addressed using their unique ID.
Bus masters come in a variety of configurations including serial, parallel, i2c, network or USB adapters.
OWFSdesignOWFS is a suite of programs that designed to make the 1-wire bus and its devices easily accessible. The
underlying principle is to create a virtual filesystem, with the unique ID being the directory, and the
individual properties of the device are represented as simple files that can be read and written.
Details of the individual slave or master design are hidden behind a consistent interface. The goal is to
provide an easy set of tools for a software designer to create monitoring or control applications. There
are some performance enhancements in the implementation, including data caching, parallel access to bus
masters, and aggregation of device communication. Still the fundamental goal has been ease of use,
flexibility and correctness rather than speed.
DS1921Thermochron
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.
Family Code
21
Name
DS1921 - Thermochron temperature logging iButton.
See Also
Programsowfs(1)owhttpd(1)owftpd(1)owserver(1)owdir(1)owread(1)owwrite(1)owpresent(1)owtap(1)Configurationandtestingowfs(5)owtap(1)owmon(1)Languagebindingsowtcl(3)owperl(3)owcapi(3)ClocksDS1427(3)DS1904(3)DS1994(3)DS2404(3)DS2404S(3)DS2415(3)DS2417(3)IDDS2401(3)DS2411(3)DS1990A(3)MemoryDS1982(3)DS1985(3)DS1986(3)DS1991(3)DS1992(3)DS1993(3)DS1995(3)DS1996(3)DS2430A(3)DS2431(3)DS2433(3)DS2502(3)DS2506(3)DS28E04(3)DS28EC20(3)SwitchesDS2405(3)DS2406(3)DS2408(3)DS2409(3)DS2413(3)DS28EA00(3)InfernoEmbedded(3)TemperatureDS1822(3)DS1825(3)DS1820(3)DS18B20(3)DS18S20(3)DS1920(3)DS1921(3)DS1821(3)DS28EA00(3)DS28E04(3)EDS0064(3)EDS0065(3)EDS0066(3)EDS0067(3)EDS0068(3)EDS0071(3)EDS0072(3)MAX31826(3)HumidityDS1922(3)DS2438(3)EDS0065(3)EDS0068(3)VoltageDS2450(3)ResistanceDS2890(3)Multifunction(current,voltage,temperature)DS2436(3)DS2437(3)DS2438(3)DS2751(3)DS2755(3)DS2756(3)DS2760(3)DS2770(3)DS2780(3)DS2781(3)DS2788(3)DS2784(3)CounterDS2423(3)LCDScreenLCD(3)DS2408(3)CryptoDS1977(3)PressureDS2406(3)TAI8570(3)EDS0066(3)EDS0068(3)MoistureEEEF(3)DS2438(3)
Special Properties
about/measuringread-only,yes-no
Is this DS1921 currently measuring a temperature?
about/resolutionread-only,floatingpoint
What is the resolution of the temperature measurments (in the current temperature scale).
about/samplesread-only,unsignedinteger
How many total temperature measurements has this DS1921 performed?
about/temphighread-only,floatingpoint
Highest temperature this DS1921 can measure (in the current temperature scale).
about/templowread-only,floatingpoint
Lowest temperature this DS1921 can measure (in the current temperature scale).
about/versionread-only,ascii
Specific version of this DS1921.clock/dateread-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/runningread-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/udateread-write,unsignedinteger
A numeric representation of clock/date
The number of seconds in UNIX time (since Jan 1, 1970).
histogram/counts.0...histogram/counts.62histogram/counts.ALLread-only,unsignedinteger
The number of samples in the current mission whose temperature fell within the histogram/temperature to
histogram/temperature+histogram/gap range.
histogram/elementsread-only,unsignedinteger
The number of bins in the histogram. Always 63.
histogram/gapread-only,floatingpoint
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.62histogram/temperature.ALLread-only,floatingpoint
Lower limit of the temperature range for the corresponding histogram bin. In the current temperature
scale.
log/date.0...log/date.2047log/date.ALLread-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/elementsread-only,unsignedinteger
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/sampleslog/temperature.0...log/temperature.2047log/temperature.ALLread-write,floatingpoint
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.2047log/udate.ALLread-write,unsignedinteger
A numeric representation of log/date
The number of seconds in UNIX time (since Jan 1, 1970).
memoryread-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.11overtemp/count.ALLundertemp/count.0...undertemp/count.11undertemp/count.ALLread-only,unsignedinteger
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.11overtemp/end.ALLundertemp/end.0...undertemp/end.11undertemp/end.ALLread-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.11overtemp/date.ALLundertemp/date.0...undertemp/date.11undertemp/date.ALLread-only,ascii
Time that the Thermochron went out of range during the current mission. See clock/date for format.
overtemp/elementsundertemp/elementsread-only,unsignedinteger
Number of entries (0 to 12) in the overtemp or undertemp array.
overtemp/temperatureundertemp/temperatureread-write,floatingpoint
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.11overtemp/udate.ALLundertemp/udate.0...undertemp/udate.11undertemp/udate.ALLread-only,unsignedinteger
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.15pages/page.ALLread-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.
temperatureread-only,floatingpoint
Last temperature explicitly requested. Only available when the mission is not in progress. Value returned
in in the current temperature scale.
Standard Properties
addressr_addressread-only,ascii
The entire 64-bit unique ID. Given as upper case hexadecimal digits (0-9A-F).
address starts with the family code
raddress is the address in reverse order, which is often used in other applications and labeling.
crc8read-only,ascii
The 8-bit error correction portion. Uses cyclic redundancy check. Computed from the preceding 56 bits of
the unique ID number. Given as upper case hexadecimal digits (0-9A-F).
familyread-only,ascii
The 8-bit family code. Unique to each type of device. Given as upper case hexadecimal digits (0-9A-F).
idr_idread-only,ascii
The 48-bit middle portion of the unique ID number. Does not include the family code or CRC. Given as
upper case hexadecimal digits (0-9A-F).
rid is the id in reverse order, which is often used in other applications and labeling.
locatorr_locatorread-only,ascii
Uses an extension of the 1-wire design from iButtonLink company that associated 1-wire physical
connections with a unique 1-wire code. If the connection is behind a LinkLocator the locatorwillshowaunique8-bytenumber(16characterhexadecimal)startingwithfamilycodeFE.
If no LinkLocator is between the device and the master, the locator field will be all FF.
rlocator is the locator in reverse order.
present(DEPRECATED)read-only,yes-no
Is the device currently present on the 1-wire bus?
typeread-only,ascii
Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be
distiguished.
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]] | address | crc8 | id | locator | r_address | r_id | r_locator | type ]]
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