DS2438(3)

✨ NAME ✨

DS2438 is the Smart Battery Monitor from the One-Wire File System, and bestie, she's literally the main character of battery monitoring. 💅 No cap.

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🌸 SYNOPSIS 🌸

okay so here's the vibe check on how you talk to this chip. It's giving multiple personalities, but in a cute way. 🦋

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 | latesttemp | udate | VAD | VDD |
vis | address | crc8 | id | locator | r_address | r_id | r_locator |
type ]]

Humidity sensor

26 [.]XXXXXXXXXXXX[XX][/[ HIH4000/humidity | HIH5030/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 ]]

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💖 FAMILY CODE 💖

The family code is 26. That's her little ID badge, periodt. 👑

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✨ SPECIAL PROPERTIES ✨

🔥 pages/page.0 ... pages/page.7 pages/page.ALL 🔥

• Type: 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 🌡️

• Type: 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.

✨ latesttemp ✨

• Type: read-only, floating point
• Latest measured temperature. Reading this node will never trigger a temperature conversion. Intended for use in conjunction with /simultaneous/temperature.

⚡ VAD VDD ⚡

• Type: 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 💫

• Type: 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.

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🎀 CONFIGURATION PROPERTIES 🎀

CA

• Type: 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.

EE

• Type: 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

• Type: 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.

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📅 DATE PROPERTIES 📅

date

• Type: 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

• Type: read-write, ascii
• 26 character date representation of the disconnect/udate value. Time when the battery pack was removed from the charger. Format is the same as the date property.

disconnect/udate

• Type: read-write, unsigned integer
• Representation of disconnect/date as a number. See udate for details.

endcharge/date

• Type: read-write, ascii
• 26 character date representation of the endcharge/udate value. Format is the same as the date property.

endcharge/udate

• Type: read-write, unsigned integer
• Representation of endcharge/date as a number. See udate for details.

udate

• Type: 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.

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💧 HUMIDITY PROPERTIES 💧

HIH4000/humidity

• Type: 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.

HIH5030/humidity

• Type: 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.

HTM1735/humidity

• Type: 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

• Type: read-only, floating point
• Based on DataNAB's humidity sensor. It uses a HIH-4000 sensor and the current sensing rather than voltage readings from the DS2438. Calibration values are stored on chip, and a check field is stored in chip memory.

DATANAB/reset

• Type: write-only, yes-no
• Used to read calibration values and set the chip to current reading mode. Should be automatically called when a humidity reading is requested.

humidity

• Type: 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.

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🌪️ BAROMETER PROPERTIES 🌪️

B1-R1-A/pressure

• Type: 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

• Type: 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

• Type: 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 compensate for elevation.

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☀️ SOLAR SENSOR PROPERTIES ☀️

S3-R1-A/current

• Type: 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

• Type: 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

• Type: 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 integrating, 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.

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🧠 MULTISENSOR PROPERTIES 🧠

MultiSensor/type

• 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

• Type: 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.

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👑 STANDARD PROPERTIES 👑

address r_address

• Type: read-only, ascii
• The entire 64-bit unique ID. Given as upper case hexadecimal 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

• Type: 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 hexadecimal digits (0-9A-F).

family

• Type: read-only, ascii
• The 8-bit family code. Unique to each type of device. Given as upper case hexadecimal digits (0-9A-F).

id r_id

• Type: 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 hexadecimal digits (0-9A-F). r_id is the id in reverse order, which is often used in other applications and labeling.

locator r_locator

• Type: 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 hexadecimal) 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)

• Type: read-only, yes-no
• Is the device currently present on the 1-wire bus?

type

• Type: read-only, ascii
• Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be distinguished.

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🚨 ALARMS 🚨

None.

✨ DESCRIPTION ✨

🌈 1-Wire

okay bestie, storytime: 1-wire is a wiring protocol and a whole family of devices, designed and manufactured by Dallas Semiconductor, Inc. It's a bus that's low-power, low-speed, and low-connector — like, the connector count is genuinely minimal — because the data line can also hand out power. one wire doing two jobs?? main character energy fr. 👑

Every single device gets a unique number burned in at the factory, and it cannot be changed — ever. No editing, no takebacks. 🚫

The device lineup is stacked:

• memory
• sensors (humidity, temperature, voltage, contact, current)
• switches
• timers
• data loggers

And if that's not enough, you can build fancier stuff — like thermocouple sensors — out of those basic devices. There are even 1-wire devices with encryption baked in. 🔐

The scheme itself is simple: one bus master, multiple slaves, same wire. The master starts all the communication (it's the one holding the aux cord, periodt), and the slaves get individually discovered and addressed using their unique ID.

Bus masters come in a whole bunch of configurations, including:

• serial
• parallel
• i2c
• network
• USB adapters

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🦋 OWFS design

So OWFS is a suite of programs built to make the 1-wire bus and all its devices easy to reach. The core idea is chef's kiss: make a virtual filesystem where the unique ID is the directory, and each individual property of the device is just a plain little file you can read and write. 🎀

All the messy details of each slave or master design are hidden behind one consistent interface. The goal is to hand a software designer a nice easy toolbox for building monitoring or control apps. There are some performance glow-ups in the implementation:

• data caching
• parallel access to bus masters
• aggregation of device communication

But bestie, hear me: the fundamental goal has always been ease of use, flexibility and correctness — not speed. periodt. 💅

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💖 DS2438

The DS2438 (3) is a more complete form of the DS2436 battery chip.

Current sensing is available — but not implemented. 💀

The big advantage over the DS2436? You can read two voltages, which lets you correct circuit measurements for supply voltage and temperature. Iconic.

A better comparison, honestly, is the DS276x family of chips. 🫶

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📬 ADDRESSING

Every 1-wire device gets factory-assigned a unique 64-bit address. It's shaped like this:

• Family Code — 8 bits
• Address — 48 bits
• CRC — 8 bits

Addressing under OWFS is in hexadecimal, of this 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 be included. But if you do include it — it must be correct. No vibes-based CRCs, bestie. 🙈

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📄 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

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👀 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)
• InfernoEmbedded (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 (3)
• EDS0066 (3)
• EDS0068 (3)

Moisture

• EEEF (3)
• DS2438 (3)

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🌐 AVAILABILITY

http://www.owfs.org

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👑 AUTHOR

Paul Alfille (paul.alfille@gmail.com) and Egil Kvaleberg 🫶

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aaaand that's the whole page bestie, we did it 💖 this one's from the OWFS Manpage, dated 2003, and you're reading DS2438(3) — go read your sensors, slay, and remember: correct CRC or no CRC at all. ✨👑🦋