DS2438(3) One-Wire File System DS2438(3)
NAME
DS2438 - Smart Battery Monitor
SYNOPSIS
Temperature Voltages and Current.
26 [.]XXXXXXXXXXXX[XX][/[ CA | EE | date | disconnect/date | disconnect/udate | endcharge/date | endcharge/udate | IAD | offset |
pages/page.[0-7|ALL] | temperature | udate | VAD | VDD | vis | address | crc8 | id | locator | r_address | r_id | r_locator | type ]]
Humidity sensor
26 [.]XXXXXXXXXXXX[XX][/[ HIH4000/humidity | HTM1735/humidity | DATANAB/reset | DATANAB/humidity | humidity | temperature ]]
Barometer
26 [.]XXXXXXXXXXXX[XX][/[ B1-R1-A/pressure | B1-R1-A/gain | B1-R1-A/offset | ]]
Light
26 [.]XXXXXXXXXXXX[XX][/[ S3-R1-A/current | S3-R1-A/illuminance | S3-R1-A/gain ]]
FAMILY CODE
26
SPECIAL PROPERTIES
pages/page.0 ... pages/page.7 pages/page.ALL
read-write, binary
Memory is split into 8 pages of 8 bytes each. Only the pages 3-7 are really available, and some of that appears to be reserved. See the
datasheet for details.
ALL is an aggregate of the pages. Each page is accessed sequentially.
temperature
read-only, floating point
Temperature read by the chip at high resolution (~13 bits). Units are selected from the invoking command line. See owfs(1) or owhttpd(1)
for choices. Default is Celsius. Conversion takes ~20 msec.
VAD VDD
read-only, floating point
Voltage read (~10 bits) at the one of the chip's two supply voltages. Range VDD= 2.4V to 10V, VAD=1.5 to 10V.
vis
read-only, floating point
Current sensor reading, as a voltage difference. Value is in volts.
Actual current depends on Rsens resistor (see datasheet).
The formula for current is I = vis / Rsens
with units in Amps and Ohms.
Current measurement will be temporarily enabled (see Ienable ) if not currently enabled (pun intended) for this reading.
CONFIGURATION PROPERTIES
CA
read-write, yes-no
Current Accumulator Configuration flag bit. If "on" (1) current is stored in page 7 bytes 4-7. If "off" (0) that page can be used for gen-
eral storage. See the datasheet for more information.
EE
read-write, yes-no
Current Accumulator Shadow flag bit. If "on" (1) current reading is stored to EEPROM. If "off" (0) that data will be lost when chip loses
power. See the datasheet for more information
IAD
read-write, yes-no
Current A/D Control flag bit. If "on" (1) current measured at 36.41 Hz. If "off" (0) current measurements won't be made. See the datasheet
for more information.
DATE PROPERTIES
date
read-write, ascii
26 character date representation of the counter value. Increments once per second.
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)
disconnect/date
read-write, ascii
26 character date representation of the disconnect/udate value. Time when the battery pack waws removed from the charger. Format is the
same as the date property.
disconnect/udate
read-write, unsigned integer
Representation of disconnect/date as a number. See udate for details.
endcharge/date
read-write, ascii
26 character date representation of the endcharge/udate value. Format is the same as the date property.
endcharge/udate
read-write, unsigned integer
Representation of endcharge/date as a number. See udate for details.
udate
read-write, unsigned integer
Time represented as a number. udate increments once per second.
Usually set to unix time standard: number of seconds since Jan 1, 1970. The date field will be the unix representation (ascii text) of
udate and setting either will change the other.
HUMIDITY PROPERTIES
HIH4000/humidity
read-only, floating point
Relative humidity, as percent (1-100 scale).
This value is for a design based on Honeywell's HIH-4000 humidity sensor.
HTM1735/humidity
read-only, floating point
Relative humidity, as percent (1-100 scale).
This value is for a design based on Humirel's HTM-1735 humidity sensor.
DATANAB/humidity
read-only, floating point
Based on DataNAB's humidity sensor. It uses a HIH-4000 sensor and the current sensning rather than voltage readings from the DS2438. Cali-
bration values are stored on chip, and a check field is stored in chip memory.
DATANAB/reset
write-only, yes-no
Used to read calibration values and set the chip to current reading more. Should be automatically called when a humidity reading is
requested.
humidity
read-only, floating point
Relative humidity, as percent (1-100 scale).
The DS2438 actually does not read humidity, but a widely available and publicised circuit based on the chip, does. This design is for the
common Honeywell HIH-3610 humidity chip. The mostly compatible HIH-4000 chip uses different temperature compensation, so is better read
from the HIH4000/humidity value. See the datasheets for details.
If the chip is instead a DATANAB design, the DATANAB/humidity value will be automatically used.
BAROMETER PROPERTIES
B1-R1-A/pressure
read-only, floating point
Pressure reading, as milli-bars, or other unit depending on settings/units/pressure_scale.
This value is for the B1-R1-A barometer from Hobby-Boards, and assumes the standard calibration.
B1-R1-A/gain
read/write, floating point
Calibration of pressure gain, as signed number, expressed as the same units as B1-R1-A/pressure per volt.
This value will be multiplied with the measured voltage to get the B1-R1-A/pressure reading. It may have to be fine tuned for calibration
purposes, although with the standard sensor, it will often be good enough to keep it as is.
B1-R1-A/offset
read/write, floating point
Calibration of pressure offset, as signed number, same units as B1-R1-A/pressure.
This value will be added to the B1-R1-A/pressure reading. The default value is 904.7 millibars, which may be altered to to compensate for
elevation.
SOLAR SENSOR PROPERTIES
S3-R1-A/current
read-only, floating point
Photo-diode current, in micro-amperes.
This value is for the S3-R1-A solar radiation sensor from Hobby-Boards. Due to noise and offsets, this value may read as a negative number
in low light conditions. The offset register can be modified to reduce the offset as much as possible.
S3-R1-A/illumination
read-only, floating point
Illumination, in lux. Always a positive number.
This value is the lux reading from the solar sensor, taking S3-R1-A/gain into consideration.
S3-R1-A/gain
read/write, floating point
Calibration of photo-diode gain expressed as lux per micro-amperes. The default value is for the SFH203P photo-diode from Osram, used
bare. A different gain may be used for instance to compensate for an integrathing, white sphere placed over the diode.
This value is for the S3-R1-A solar radiation sensor from Hobby-Boards, using the SFH203P photo-diode from Osram.
MULTISENSOR PROPERTIES
MultiSensor/type
read-only, ascii
For iButtonLink's MultiSensor line of 1-wire devices, give the specific configuration based on a data byte set in memory. (Byte 0 of page
3). This can help interpretation of the sensor values, distinguishing, current from water from light.
offset
read-write, integer
Correction for current readings. A value between -256 and 255. See the datasheet for details. Should be set to the negative of a true zero
current reading.
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.
DS2438
The DS2438 (3) is a more complete form of the DS2436 battery chip. Current sensing is available, but not implemented. The major advantage
compared to the DS2436 is that two voltages can be read, allowing correcting circuit nmeasurements to supply voltage and temperature. A
better comparison is the DS276x family of chips.
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
http://goo.gl/o9DH0 (Redirects to 009012_2.pdf PDF file on honeywell.com website)
http://www.phanderson.com/hih-4000.pdf
http://www.humirel.com/product/fichier/HTM1735%20RevG%20.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) Egil Kvaleberg
OWFS Manpage 2003 DS2438(3)