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 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.
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
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)
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) 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 EDS0066 (3) EDS0068 (3)
Moisture¶
EEEF (3) DS2438 (3)
AVAILABILITY¶
http://www.owfs.org
AUTHOR¶
Paul Alfille (paul.alfille@gmail.com)