Ubuntu Manpage: DS1921 - Thermachron temperature logging iButton.

Provided by: owfs-doc_2.8p15-1ubuntu4_all

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

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 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  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 (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 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

AVAILABILITY

       http://www.owfs.org

AUTHOR

       Paul Alfille (paul.alfille@gmail.com)