DS1921-Thermachron(3)					       One-Wire File System					     DS1921-Thermachron(3)

NAME

       DS1921 - Thermachron 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]] | address | crc8 | id | locator
       | r_address | r_id | r_locator | type ]]

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).

   abount/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  index-
       ing 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 durring 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

   address
   r_address
       read-only, ascii
       The entire 64-bit unique ID. Given as upper case hexidecimal digits (0-9A-F).
       address starts with the family code
       r address is the address in reverse order, which is often used in other applications and labeling.

   crc8
       read-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 hexidecimal digits (0-9A-F).

   family
       read-only, ascii
       The 8-bit family code. Unique to each type of device. Given as upper case hexidecimal digits (0-9A-F).

   id
   r_id
       read-only, ascii
       The  48-bit  middle portion of the unique ID number. Does not include the family code or CRC. Given as upper case hexidecimal digits (0-9A-
       F).
       r id is the id in reverse order, which is often used in other applications and labeling.

   locator
   r_locator
       read-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 Link Locator the locator will show a unique 8-byte number (16 character hexidecimal) starting with family code
       FE.
       If no Link Locator is between the device and the master, the locator field will be all FF.
       r locator is the locator in reverse order.

   present (DEPRECATED)
       read-only, yes-no
       Is the device currently present on the 1-wire bus?

   type
       read-only, ascii
       Part name assigned by Dallas Semi. E.g.	DS2401 Alternative packaging (iButton vs chip) will not be distiguished.

ALARMS

       None.

DESCRIPTION

   1-Wire
       1-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 (humid-
       ity, 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 bus master 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.

   OWFS design
       OWFS is a suite of programs that designed to make the 1-wire bus and its devices easily accessible. The underlying priciple 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 fundemental goal has  been  ease  of  use,
       flexibility and correctness rather than speed.

   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 the to 62-bin histogram. more complete form of
       the  DS2438 (3) battery chip. Current sensing is available, but not implemented. The major advantage compared to the DS2436 (3) is that two
       voltages can be read, allowing correcting circuit nmeasurements to supply voltage and temperature.

ADDRESSING

       All 1-wire devices are factory assigned a unique 64-bit address. This address is of the form:

       Family Code
	      8 bits

       Address
	      48 bits

       CRC    8 bits

       Addressing under OWFS is in hexidecimal, 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.

DATASHEET

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

SEE ALSO

   Programs
       owfs (1) owhttpd (1) owftpd (1) owserver (1) owdir (1) owread (1) owwrite (1) owpresent (1) owtap (1)

   Configuration and testing
       owfs (5) owtap (1) owmon (1)

   Language bindings
       owtcl (3) owperl (3) owcapi (3)

   Clocks
       DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)

   ID
       DS2401 (3) DS2411 (3) DS1990A (3)

   Memory
       DS1982 (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)

   Switches
       DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)

   Temperature
       DS1822  (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)

   Humidity
       DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)

   Voltage
       DS2450 (3)

   Resistance
       DS2890 (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)

   Counter
       DS2423 (3)

   LCD Screen
       LCD (3) DS2408 (3)

   Crypto
       DS1977 (3)

   Pressure
       DS2406 (3) -- TAI8570 EDS0066 (3) EDS0068 (3)

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)

OWFS Manpage							       2005						     DS1921-Thermachron(3)