Ubuntu Manpage: DS1821 - Programmable Digital Thermostat and Thermometer

Provided by: owfs-doc_3.2p4+dfsg1-4.3build2_all

NAME

       DS1821 - Programmable Digital Thermostat and Thermometer

SYNOPSIS

       Thermostat.

       thermostat   [/[  temperature  |  temphigh  |  templow  |  temphighflag  |  templowflag  |
       thermostatmode | polarity | 1shot ]]

FAMILY CODE

       none

SPECIAL PROPERTIES

temperature
read-only, floating point
9-bit resolution temperature. Units are selected from the invoking command line. See
owfs(1) or owhttpd(1) for choices. Default is Celsius. Conversion takes 1 second.

temphigh templow
read-write. floating point
Temperature limits for alarms. Units are selected from the invoking command line. See
owfs(1) or owhttpd(1) for choices. Default is Celsius.
Note that alarms are not implemented.

temphighflag, templowflag
read-write. yes-no
temphighflag goes to 1 when temperature exceeds temphigh and stays at 1 until it is reset
by writing it to zero. This state persists across power cycles and operates in both
1-wire and thermostat modes. templowflag behaves in the same way, monitoring the
temperature with respect to templow.

thermostatmode
read-write. yes-no
When this bit is set to 1 the chip will enter thermostat mode on the next power-up. See
the datasheet for further information on thermostat mode. NOTE: Once the DS1821 has
entered thermostat mode it cannot be taken out back to 1-wire mode using a 1-wire
interface. Special electrical incantations on the power and data lines must be performed
that are not possible with a normal 1-wire bus master. A special circuit is required - see
the datasheet for complete details.

polarity
read-write. yes-no
Controls the output sense of the thermostat output (DQ) while in thermostat mode. If
polarity is 0 the output is active low. If it is 1, active high.

1shot
read-write. yes-no
If this bit is 1, a START CONVERT command will begin a conversion and the chip will enter
a low power state when the conversion is complete. If the bit is 0 then START CONVERT
will begin a conversion and start another one as soon as it is done. STOP CONVERSION must
be performed to get the conversion cycle to stop. This interface automatically issues a
STOP CONVERSION command when going out of continuous mode.

TEMPERATURE ALARM LIMITS

       When  the device exceeds either temphigh or templow temperature threshold the device is in
       the alarm state, and will appear in the alarm directory. This provides an easy way to poll
       for  temperatures  that  are  unsafe, especially if simultaneous temperature conversion is
       done.

       Units for the temperature alarms are in the  same  temperature  scale  that  was  set  for
       temperature measurements.

       Temperature  thresholds  are stored in non-volatile memory and persist until changed, even
       if power is lost.

   temphigh
       read-write, integer
       Shows or sets the lower limit for the high temperature alarm state.

   templow
       read-write, integer
       Shows or sets the upper limit for the low temperature alarm state.

STANDARD PROPERTIES

   type
       read-only, ascii
       Chip type: DS1821

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.

DS1821
The DS1821 (3) is a unique 1-wire device. It is unaddressable, and therefore there can be
only one on a given bus. It is meant to be programmed once using 1-wire and then
permanently installed in a thermostat circuit. Once in thermostat mode, it is no longer
programmable from a 1-wire interface. It is possible to recover it into 1-wire mode but
only with a special circuit.

ADDRESSING

       Unlike all other 1-wire chips, the ,B DS1821 (3) has no unique address. It is addressed as
       thermostat and will not announce itself in device discovery (directory listing).

DATASHEET

       http://pdfserv.maxim-ic.com/en/ds/DS1821.pdf

   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)