DS2438 − Smart Battery Monitor
26 [.]XXXXXXXXXXXX[XX][/[ CA | EE | date | disconnect/date | disconnect/udate | endcharge/date | endcharge/udate | IAD | offset | pages/page.[0-7|ALL] | temperature | latesttemp | udate | VAD | VDD | vis | ]]
26 [.]XXXXXXXXXXXX[XX][/[ HIH4000/humidity | HIH5030/humidity | HTM1735/humidity | DATANAB/reset | DATANAB/humidity | humidity | temperature ]]
26 [.]XXXXXXXXXXXX[XX][/[ B1-R1-A/pressure | B1-R1-A/gain | B1-R1-A/offset | ]]
26 [.]XXXXXXXXXXXX[XX][/[ S3-R1-A/current | S3-R1-A/illuminance | S3-R1-A/gain ]]
26
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.
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.
read-only,
floating point
Latest measured temperature. Reading this node will never
trigger a temperature conversion. Intended for use in
conjunction with /simultaneous/temperature.
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.
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.
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 general
storage. See the datasheet for more information.
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
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.
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)
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.
read-write,
unsigned integer
Representation of disconnect/date as a number. See
udate for details.
read-write,
ascii
26 character date representation of the
endcharge/udate value. Format is the same as the
date property.
read-write,
unsigned integer
Representation of endcharge/date as a number. See
udate for details.
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.
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.
read-only,
floating point
Relative humidity, as percent (1-100 scale).
This value is for a design based on Honeywell’s
HIH-5030/5031 humidity sensor.
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.
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. Calibration values are stored on chip, and
a check field is stored in chip memory.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
None.
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 one to correct circuit measurements for supply voltage and temperature. A better comparison is the DS276x family of chips.
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
http://www.owfs.org
Paul Alfille ([email protected]) Egil Kvaleberg