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 ]]


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 ]]




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.


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

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 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.




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.


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).


read-only, ascii

The 8-bit family code. Unique to each type of device. Given as upper case hexidecimal digits (0-9A-F).



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.



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?


read-only, ascii

Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be distiguished.





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.


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.


All 1-wire devices are factory assigned a unique 64-bit address. This address is of the form:

Family Code

8 bits


48 bits


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 (Redirects to 009012_2.pdf PDF file on website)



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)


DS1427 (3) DS1904(3) DS1994 (3) DS2404 (3) DS2404S (3) DS2415 (3) DS2417 (3)


DS2401 (3) DS2411 (3) DS1990A (3)


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)


DS2405 (3) DS2406 (3) DS2408 (3) DS2409 (3) DS2413 (3) DS28EA00 (3)


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)


DS1922 (3) DS2438 (3) EDS0065 (3) EDS0068 (3)


DS2450 (3)


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)


DS2423 (3)

LCD Screen

LCD (3) DS2408 (3)


DS1977 (3)


DS2406 (3) TAI8570 EDS0066 (3) EDS0068 (3)


EEEF (3) DS2438 (3)



Paul Alfille ([email protected]) Egil Kvaleberg