DS2438(3) One-Wire File System DS2438(3)NAMEDS2438 - Smart Battery Monitor
SYNOPSIS
Temperature Voltages and Current.
26 [.]XXXXXXXXXXXX[XX][/[ CA | EE | date | disconnect/date | discon‐
nect/udate | endcharge/date | endcharge/udate | IAD | offset |
pages/page.[0-7|ALL] | temperature | udate | VAD | VDD | vis | ]]
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 sen‐
sor.
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. Calibra‐
tion 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 com‐
mon 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 set‐
tings/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 inte‐
grathing, 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, cur‐
rent 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 PROPERTIESALARMS
None.
DESCRIPTIONDS2438
The DS2438 (3) is a more complete form of the DS2436 battery chip. Cur‐
rent sensing is available, but not implemented. The major advantage
compared to the DS2436 is that two voltages can be read, allowing one
to correct circuit measurements for supply voltage and temperature. A
better comparison is the DS276x family of chips.
ADDRESSINGDATASHEET
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 honey‐
well.com website)
http://www.phanderson.com/hih-4000.pdf
http://www.humirel.com/product/fichier/HTM1735%20RevG%20.pdf
SEE ALSOAVAILABILITY
http://www.owfs.org
AUTHOR
Paul Alfille (paul.alfille@gmail.com) Egil Kvaleberg
OWFS Manpage 2003 DS2438(3)
