--- name: "DS1921" section: "3" platform: "linux" package: "owfs-doc" version: "3.2p4+dfsg1-6" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/DS1921" --- # DS1921(3) Thermochron temperature logging iButton. ## 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\[0-11\|ALL\]\]** \| **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). ### 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 ### address ### r\_address *read-only, ascii*\ The entire 64-bit unique ID. Given as upper case hexadecimal 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 hexadecimal digits (0-9A-F). ### family *read-only, ascii*\ The 8-bit family code. Unique to each *type* of device. Given as upper case hexadecimal 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 hexadecimal 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 hexadecimal) 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 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. ### 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 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 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. ## 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) InfernoEmbedded (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) MAX31826 (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 (3) EDS0066 (3) EDS0068 (3)** ### Moisture **EEEF (3) DS2438 (3)** ## AVAILABILITY http://www.owfs.org ## AUTHOR Paul Alfille (paul.alfille@gmail.com)